review article recent development of graphene-based...

Review ArticleRecent Development of Graphene-Based Cathode Materials forDye-Sensitized Solar Cells

Man-Ning Lu12 Chin-Yu Chang1 Tzu-Chien Wei2 and Jeng-Yu Lin1

1Department of Chemical Engineering Tatung University No 40 Section 3 Chung Shan North Road Taipei City 104 Taiwan2Department of Chemical Engineering National Tsing-Hua University Hsinchu 300 Taiwan

Correspondence should be addressed to Jeng-Yu Lin jylinttuedutw

Received 10 December 2015 Accepted 13 March 2016

Academic Editor Vincenzo Baglio

Copyright copy 2016 Man-Ning Lu et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Dye-sensitized solar cells (DSSCs) have attracted extensive attention for serving as potential low-cost alternatives to silicon-basedsolar cells As a vital role of a typical DSSC the counter electrode (CE) is generally employed to collect electrons via the externalcircuit and speed up the reduction reaction of I

3

minus to Iminus in the redox electrolyte The noble Pt is usually deposited on a conductiveglass substrate as CE material due to its excellent electrical conductivity electrocatalytic activity and electrochemical stabilityTo achieve cost-efficient DSSCs reasonable efforts have been made to explore Pt-free alternatives Recently the graphene-basedCEs have been intensively investigated to replace the high-cost noble Pt CE In this paper we provided an overview of studies onthe electrochemical and photovoltaic characteristics of graphene-based CEs including graphene graphenePt graphenecarbonmaterials grapheneconducting polymers and grapheneinorganic compounds We also summarize the design and advantages ofeach graphene-based material and provide the possible directions for designing new graphene-based catalysts in future researchfor high-performance and low-cost DSSCs

1 Introduction

Nowadays photovoltaic (PV) technology is considered asone of the widespread and efficient approaches to produceelectricity from solar energy due to the increasing attention tolow-carbon economy and renewable energy commercializa-tion On the basis of the basal technology PV devices are gen-erally classified as first- second- and third-generation solarcells Since dye-sensitized solar cell (DSSC) was first reportedin 1991 [1] it has been regarded as one of the promisingthird-regeneration solar cells due to low manufacturing costfacile fabrication processes relatively high power conversionefficiency (PCE) and wide spectral response in visible lightregion for indoor applications [2]

As illustrated in Figure 1 a typical DSSC basically con-tains a nanocrystalline semiconductor oxide a dye sensitizeran electrolyte redox couple and a catalystmaterial as cathodealso called counter electrode (CE) To achieve high cellefficiency the individual components in DSSCs are necessaryto be optimized [3] As a crucial component in DSSCs themain functions of a CE is to transport electrons from external

circuit and catalyze the reduction reaction of I3

minus to Iminus for dyeregeneration The overall I

3

minus reduction reaction occurringon the CE surface can be described in (1) Equation (1) canbe divided into the following steps (as depicted in (2)ndash(5))involved in the reduction mechanism of I

3

minus [4]

I3

minus+ 2eminus larrrarr 3Iminus (1)

I3

minuslarrrarr I

2+ Iminus (2)

I2+ 2CElarrrarr I (CE) + I (CE) (3)

I (CE) + eminus larrrarr Iminus (CE) (4)

Iminus (CE) larrrarr Iminus + CE (5)

Equation (2) represents the solution phase reaction whichhas been verified to be relatively fast and considered to be inequilibrium [4] Then I

2dissociates into two surface I atoms

upon adsorption on the CE surface (designated as I(CE)) via(3) and subsequently I atoms on the CE surface are reducedto Iminus ions adsorbed on the CE surface through one-electron

Hindawi Publishing CorporationJournal of NanomaterialsVolume 2016 Article ID 4742724 21 pageshttpdxdoiorg10115520164742724

2 Journal of Nanomaterials

Gla

ssFT

O

Gla

ssFT

OC

ount

er el

ectro

de

eminuseminus

Iminus

Iminus

Load

Redox couple

h

I3minus

I3minus

Iminusand I3minus

Figure 1 Schematic illustration of the operation principle of aDSSC

transfer as depicted in (4) After that the adsorbed Iminus ionsare desorbed from the CE surface to be the solvated Iminus ions inelectrolyte as illustrated in (5)

On the basis of the functions of a CE and the reductionmechanism of I

3

minus an efficient CE should exhibit both highelectrical conductivity and electrocatalytic activity to keep alow overpotential and to minimize energy loss in DSSCs [5]Generally Pt has been proven to be an excellent CE materialin DSSCs due to its high electrical conductivity and excellentelectrocatalytic activity as well as great electrochemical stabil-ity As a noble and sparse metal however the high cost of Pt(ca $50000Kg) restricts its practical applicationsThereforemuch effort has been devoted to exploring the efficient Pt-free CEs To date a great deal of materials including carbonmaterials [6] conducting polymers [7ndash11] and inorganicmaterials [12ndash18] have been introduced as alternative CEmaterials to Pt

Compared to other conventional carbon materials gra-phene a single-layer structure of two-dimensional graphitepossesses unique features of the strong mechanical strengthhigh electrical and thermal conductivity large surface areaand high optical transmittance [19] Therefore it has beenwidely incorporated in the fields ofmicroelectronic and opto-electronic devices energy storage and conversion materials[20 21] SinceAksayrsquos group revealed the functional graphenesheets (FGSs) as CE material for efficiently catalyzing theredox reaction of I

3

minusIminus in 2010 a variety of graphene-basedCE materials have been intensively developed for Pt-freeDSSCs [22]

In this work we comprehensively reviewed the advance ofresearch on graphene-based CE materials for Pt-free DSSCswith emphasis on composite materials

2 Graphene CEs

Graphene has been considered as one of the promising Pt-free CE alternatives in DSSCs due to its specific properties ofhigh electrical conductivity excellent electrocatalytic activitygreat anticorrosion resistance and larger surface area [24

28] In general graphene materials can be synthesized viamechanical exfoliation epitaxial growth chemical vapordeposition thermal exfoliation [29ndash32] and so forth Table 1summarizes the comparison of various graphene CEs inDSSCs For example Aksayrsquos group used thermal exfolia-tion to synthesize FGSs with defects and oxygen-containingfunction groups (hydroxyl carbonyl and epoxide) [24]Theyfound that the increase in CO ratio of FGSs is positivelyassociated with their electrocatalytic activity Neverthelessthe electrical conductivity of FGSs can be reduced by formingmore functional groups while the temperature of thermalprocessing increases over 1500∘C After the optimization ofCO ratio in FGSs the FGSs-basedDSSC reached higher PCEof 548 and fill factor (FF) of 060 than Pt-based DSSC(499 and 057) They found that the improved FF valueof the FGSs-based DSSC can be attributed to its relativelylow charge-transfer resistance (119877ct) of 064Ω cm

2 which iseven lower than that of the Pt CE (079Ω cm2) Gratzelrsquosgroup prepared an optically transparent graphene thin filmby dropping commercial graphene nanoplatelets on fluorinedoped tin oxide (FTO) glass substrates [23] They found thatthe graphene CE has amuch lower119877ct value in an ionic liquidthan in the traditional organic solvent by a factor of 5-6suggesting that the regeneration of I

3

minusIminus in an ionic liquid issuperior to that in the traditional organic solvent (as depictedin Figure 2) Choi et al [33] further prepared grapheneCEs using electrophoretic deposition followed by annealingtreatment at 200sim600∘C They found that the DSSC usingthe graphene CEs obtained after the annealing treatmentat 600∘C exhibited the optimized PCE of 569 Kaniyoorand Ramaprabhu [34] synthesized graphene with defect-rich and wrinkled structure through a thermally exfoliatedmethod Then the thermally exfoliated graphene (TEG)was suspended in Nafionethanol solution and subsequentlydropped on FTO glass substrates to form the TEG CEsThe TEG CE demonstrated 119877ct value of 117Ω cm2 whichis close to that of the Pt CE (65Ω cm2) This indicatesthat the wrinkled and defect-rich structure of TEG canprovide large surface area and high density of defect sidesfor I3

minusIminus reduction reaction and thus the electron transferkinetics at the CEelectrolyte interface is promoted Zhanget al synthesized novel 3D structure of graphene nanosheets(GNs) as CE material for DSSCs [28] The GN was preparedusing oxidative exfoliation of graphite followed by hydrazinereduction and annealing process After the optimizationof annealing temperature it can be found that the DSSCassembled with the GN CE annealed at 400∘C exhibitedthe best cell performance of 681 which is comparable tothat of the Pt-based DSSC (759) After being annealed at400∘C the GN was revealed with a unique 3D structureThissignifies that the annealed GN can afford sufficient surfacearea for I

3

minusIminus reduction reaction and therefore its 119877ct valueis significantly decreased from 3372 to 12Ω

On the other hand Xu et al [41] reported a facileand rapid microwave-assisted method to synthesize heminfunctionalized reduced graphene oxide (hemin-RGO) It wasfound that 5-layer hemin-RGO demonstrated 119877ct value ofca 7Ω comparable to that of the Pt-based CE (7Ω) Lee et

Journal of Nanomaterials 3

Table 1 Photovoltaic performance of the DSSCs assembled with various graphene CEs

CE Substrate Preparation method Redox couple Dye 119877ct (Ω cm2) FF PCE () Ref

GO-GNP FTO glass Drop-casting IminusI3

minus N3 064 060 499 [20]GNP FTO glass Drop-casting IminusI

3

minus N719 040 074 689 [29]RGO FTO glass Electrophoretic deposition IminusI

3

minus N719 3800lowast 065 569 [46]

TEG FTO glass Drop-casting IminusI3

minus N719 1170 054 282 [30]Hemin-RGO FTO glass Drop-casting IminusI

3

minus N719 612 031 245 [31]RGO FTO glass Screen-printing IminusI

3

minus N719 120 054 681 [19]RGO ITO glass Spin-coating IminusI

3

minus N719 2150 056 213 [47]3D-NFG FTO glass CVD IminusI

3

minus N719 4588 060 520 [32]VG FTO glass CVD IminusI

3

minus N719 00073 067 536 [23]Honeycomb-likestructure graphene FTO glass CVD IminusI

3

minus N719 2000lowast 037 780 [34]

N-doped graphene FTO glass CVD IminusI3

minus N719 mdash 033 312 [41]GNP FTO glass Drop-casting Co3+Co2+ Y123 350

lowast 070 930 [45]GNP FTO glass Drop-casting Co3+Co2+ Y123 330 072 940 [48]FGS FTO glass Screen-printing IminusI

3

minus N719 mdash 067 679 [20]FGS FTO glass Screen-printing Co3+Co2+ D35 mdash 065 451 [20]FGS FTO glass Screen-printing S3+S2+ D35 mdash 055 345 [20]RGO FTO glass Drop-casting Co3+Co2+ T123 127 067 930 [49]N-doped graphene FTO glass Drop-casting Co3+Co2+ YD-2-o-C8 138 072 83 [50]lowastRepresents that the unit of the 119877ct value isΩ

15

10

5

0

Curr

ent d

ensit

y (m

Ac

m2 )

00 02 04 06 08Voltage (V)

1 sun

05 sun

01 sun

Dark

PtZ946G3Z946

(a)

Curr

ent d

ensit

y (m

Ac

m2 )

1 sun

05 sun

01 sun

Dark

12

10

8

6

4

2

0

minus2

00 02 04 06 08Voltage (V)

PtZ952G3Z952

(b)

Figure 2 Current-voltage characteristics of a dye-sensitized solar cell with the platinized FTO (black lines) or G3 cathode (red lines) undervarious light intensities (a) Z946 electrolyte (b) Z952 electrolyte [23]

al fabricated 3D nanofoam of few-layer graphene (3D-NFG)with large-area coverage via the chemical vapor deposition(CVD) technique [42] The PCE of the DSSC based on the3D-NFG CE reached 52 which was even close to thatof Pt CE (57) Yu et al prepared the vertically oriented

graphene (VG) nanosheets by plasma-enhanced chemicalvapor deposition (PECVD) and the as-synthesized VG wasfound to be with large surface area and abundant oxygenfunctional groups [43] According to series of electrochem-ical characterizations including electrochemical impedance


Table 2 Photovoltaic performance of the DSSC using various Ptgraphene composite CEs


Pt NPsgraphenesheet FTO glass Electrodeposition IminusI

3

minus N3 236 059 291 [33]

PtRGO FTO glass Two-step reduction IminusI3

minus N719 3495 060 401 [51]PtNPGR FTO glass Water-ethylene method IminusI

3

minus N719 1045lowast 067 635 [52]

GNSPt-NHB FTO glass Electrospray IminusI3

minus N719 2700 066 797 [53]Pt-NPsRGO FTO glass Dry-plasma reduction IminusI

3

minus N719 062 067 856 [54]GNSPt FTO glass Electrostatic Layer-by-layer self-assembly IminusI

3

minus N719 3080 073 609 [55]PtNPGN FTO glass Electrodeposition IminusI

3

minus N719 208 068 788 [56]GNPtNPs FTO glass Polyol reduction IminusI

3

minus N719 255 070 879 [57]GNsPt ITO glass Microwave-assisted synthesischemical reduction IminusI

3

minus N719 265lowast 068 510 [58]

lowastRepresents that the unit of the 119877ct value isΩ

spectroscopy (EIS) and cyclic voltammetry (CV) the elec-trocatalytic activity of VG was systemically elucidated TheVG CE not only exhibited lower 119877ct value (73 times 10

minus3Ωm2)

than Pt-based CE but also presented higher peak current andsmaller peak-to-peak potential separation (Δ119864p) compared tothe Pt CE This signifies the excellent electrocatalytic activityofVGCEs for reduction of I

3

minus to Iminus therefore resulting in thatthe DSSC assembled with the VG CE exhibited a relativelyhigher PCE of 536 than that based on the Pt CE (436)ImpressivelyWang et al [44] synthesized the novel graphenesheet with 3D honeycomb-like structure based on a simplereaction between Li

2O and CO The PCE of the DSSC based

on the 3D graphene with honeycomb-like structure reached78 presenting its great potential as an efficient Pt-free CEin DSSC Yang et al reported anN-doped few-layer grapheneas CEmaterial in DSSCs According to the inert nature of thepristine graphene it is usually with limited defects or edgeplanes [45] Compared to the pristine graphene CE N-dopedgraphene CE can provide more electrocatalytic sites forcharge transfer between CEelectrolyte interfaces and there-fore improve the cell conversion performance Furthermorethey found that N-doped graphene in DSSC demonstratedgreat long-term stability due to the great adhesion betweengraphene materials and FTO substrate

The commonly ruthenium dyes anchored onto the pho-toelectrode with I

3

minusIminus system are considered to be withslow recombination kinetics and thus this promotes rapiddye regeneration Nevertheless the potential of I

3

minusIminus redoxcouple is 035V (versus the normal hydrogen electrodeNHE) [49] As for the oxidation potential of the ruthe-nium dye it is only ca 11 V versus NHE [46] In aDSSC the low operating potential window limits its open-circuit voltage (119881oc) (ca 07sim08V during the dye gener-ation) To enhance the 119881oc value of DSSCs redox medi-ators with more positive potential have been developedsuch as Co(bpy)

3

3+Co(bpy)3

2+ (ca 056V versus SHE)[47] Compared to a DSSC with I

3

minusIminus redox couple usingCo(bpy)

3

3+Co(bpy)3

2+ redox couple possesses larger 119881ocvalue up to 09sim1 V Kavanrsquos group developed a functionalizedgraphene CE in Co(bpy)

3

3+Co(bpy)3

2+ redox mediatorsThey reported a high-performance DSSC based on a new

system including graphene nanoplatelets (GNP) CE and pho-toanode conjunction with Y123 dye It should be noted thatthe GNP-based DSSC in the Co(bpy)

3

3+Co(bpy)3

2+ redoxmediators revealed relatively superior PCE (ca 9) to thatof the Pt-based DSSC (ca 8) signifying that the complexis a promising redox mediator for a novel type of iodine-freeDSSCs with119881oc exceeding 1 V [48] It was also found that theGNP CE exhibited lower 119877ct value and larger exchange cur-rents in Co(bpy)

3

3+Co(bpy)3

2+ electrolyte systemThis sug-gests that the GNP CE is one of potential cathode materialsin theDSSCswithCo(bpy)

3

3+Co(bpy)3

2+ electrolyte systemKavanrsquos group further reported on the improved fabricationprotocol toward optically transparent graphene-based layersyieldingwear-resistant filmswith good adhesion to FTO [50]They prepared the single-layer graphene oxide (GO) andGO-GNP composite as a result the GO-based electrodesshowed bettermechanical and electrochemical stability Afterthe aging tests GO-based electrodes have less losing inelectrocatalytic activity Moreover the best electrochemicalperformance and electrocatalytic ability of the CE preparedwith 50 of GO and 50 of NGP in Co(bpy)

3

3+Co(bpy)3

2+

electrolyte system Roy-Mayhew et al [24] fabricated theversatile functionalized graphene sheet (FGS) and employedit as CE in the DSSCs with iodine- cobalt- and sulfur-basedredox mediators As depicted in Figure 3 the FGS-basedDSSCs displayed superior photovoltaic performance to thatof the Pt-based DSSCs regardless of the electrolyte systems

3 PtGraphene Composites

To enhance the electrocatalytic activity of graphene CEsa variety of Ptgraphene composite CEs are designed andsynthesized which are summarized in Table 2 for com-parison For example Bajpai et alrsquos [54] synthesized Ptnanoparticles (NP) were deposited directly on to grapheneusing pulsed laser deposition (PLD) method Pt-NPs weredeposited uniformly over micrometer-sized graphene sheetsThey found that the graphenePt composite with 27 Ptloading showed higher PCE short-circuit current density(119869sc) and (119881oc) and no loss of the FF as compared to the cellsfabricated with standard expansive Pt CE Wan et al [55]


Functionalized graphene sheet counter electrodePlatinum counter electrode

16

12

8

4

0

N719 dye iodine-based mediator

0 02 04 06 08Potential (V)

Phot

ocur

rent

den

sity

(mA

cm

2 )

(a)

D35 dye cobalt-based mediator

0 03 06 09Potential (V)

10

8

6

4

2

0

Phot

ocur

rent

den

sity

(mA

cm

2 )Functionalized graphene sheet counter electrodePlatinum counter electrode

(b)


10

8

6

4

2

0

D35 dye sulfur-based mediator

Phot

ocur

rent

den

sity

(mA

cm

2 )


(c)

Figure 3 119869-119881 curve characteristics of DSSCs using thermally decomposed chloroplatinic acid (Pt) and FGS counter electrodes (a) I-basedmediator N719 sensitizer (b) cobased mediator D35 sensitizer (c) S-based mediator D35 sensitizer Active area is 025 cm2 [24]

synthesized graphenePt nanocompositeswith lowPt loadingvia a two-step reduction process The resultant Ptgraphenecomposite films were then coated on FTO substrates usinga simple drop-casting method at room temperature andsubsequently used as CEs in DSSCsThe Pt nanoparticles areca 4ndash20 nm in size and uniformly distributed on the surfaceof the graphene layersThe energy conversion efficiency of the

Ptgraphene-based DSSC was found to be 19 close to thatof cells with a Pt-based CE Yen et al [56] further developeda water-ethylene method to prepare a composite materialconsisting of Pt nanoparticles and graphene (PtNPGR)The PCE value (635) of the DSSCs using PtNPGR CEwas higher than Pt CE-based DSSCs (527) which wasattributed to the increase in 119869sc value by 13 Kimrsquos group


[57] prepared aqueous dispersible nanohybrids (NHBs) ofgraphene nanosheets (GNSs) and Pt nanoparticles (Pt-NPs)via the one-pot reduction of their precursors by using anenvironmentally friendly chemical vitamin C Moreoverthe GNSPt-NHBs CE was simply fabricated by a facileelectrospray approach from the as-prepared stable aqueouscolloidal dispersion of GNSPt-NHBs The main advantageof using electrospray to prepare the GNSPt-NHBs CE isthat the GNSPt-NHBs hybrid materials can be directlydeposited on the surface of FTO substrates without using anyorganic binders The Pt-NPs were observed to be robustlyattached on the surface of the GNSs The PCE of the DSSCusing the GNSsNHBs CE (797) was approximately twotimes higher than that of the DSSC with the GNSs (444)When the GNS-NHB CEs were with annealing treatmentthe PCE of the DSSC assembled with the annealed GNS-NHBs CE (891) was comparable to that of the DSSC basedon Pt CE (885) Dao et al [58] developed a simple andcontinuous dry-plasma reduction method to evenly hybridPt nanoparticles (Pt-NPs) on reduced graphene oxide (RGO)layer under atmospheric pressure andwithout using any toxicchemicals Pt-NPs with a size range of 05ndash4 nm (mostly2 nm) were found to be dispersed on the surface of RGOThe Pt-NPsRGO CE displays great electrocatalytic activityas well as excellent long-term stability The DSSC based onsuch robust and low-cost CE achieved an impressive PCEof 856 Furthermore Gong et al [103] developed a facileelectrostatic layer-by-layer self-assembly (ELSA) method toconstruct ultrathin films composed of graphene nanosheets(GNS) and Pt nanoparticles on the conductive glass as atransparent and high-performance CE After a series ofELSA treatments the as-prepared self-assembled film is thensintered and converted to graphenePt film on FTO glasssubstrateTheDSSCwith themonolayerGNSPtCE achieveda PCE of 766 which was comparable to that using theexpensive sputtered Pt CE (816) Yue et al [104] employed afacile one-step electrochemical depositionmethod to preparePt nanoparticlesgraphene nanosheets (PtNPGN) films inwhich the deposition bath was composed of H

2PtCl6and

GN After optimizing the amount of GN (ranging from 0ndash025 wt) in the deposition bath the PtNPGN-based DSSCachieved a high PCE of 788 which is increased by 21compared with a device based on traditional Pt CE Yeh etal [25] synthesized graphenePt nanoparticles (GNPtNPs)catalysts with various PtNP loadings (10ndash60wt) using apolyol reduction method As depicted in Figure 4 the DSSCwith the GNPtNPs-20 CE shows the higher PCE of 879as compared to cells with pristine GN (765) and s-Pt CEs(858) Thus the efficient and economical GNPtNPs-20nanocomposite is a potential candidate for replacing theexpensive Pt CE in DSSCs To reduce the cost and timeconsumption for production Saranya et al [105] tried toemploy a microwave-assisted exfoliation method followed bya chemical reduction by chloroplatinic acid for synthesizinggraphene nanosheets (GNs)Pt composites in which only160 s reaction time was required to the intercalation andexfoliation of the graphite to formGNsThe device assembledwith the as-prepared Pt-decorated GNs achieved a PCE of

20

18

16

14

12

10

8

6

4

2

000 01 02 03 04 05 06 07

GNGNPtNPs-20s-Pt

GNGNPtNPs-20s-Pt

120578 () Rct1 (Ω)

765 plusmn 012

879 plusmn 021

858 plusmn 015

Voc (V)

070 plusmn 002

069 plusmn 001

069 plusmn 001

(mA cmminus2) FF

1708 plusmn 041

1819 plusmn 058

1777 plusmn 037

064 plusmn 002

070 plusmn 001

070 plusmn 001

912

585

645

Cell voltage (V)

minus2 )

Phot

ocur

rent

den

sity

(mA

cm

JscCE

Figure 4 Photocurrent density-voltage curves of DSSCs with CEscontaining pristine GN GNPtNPs-20 and s-Pt obtained at100mWcmminus2 (AM 15 G) [25]

511 which is increased by 11 compared to that reportedfor other similar systems

4 GrapheneCarbon Material Composites

To achieve high-performance of graphene-based CEs lotsof research has been reported on hybrid graphene withother kinds of carbon materials including carbon nanotubes(CNTs) carbon black and mesoporous carbon For instancethe combination of 1-D CNT with 2-D graphene has beenproposed to promote the electron transfer and ionic dif-fusion and therefore facilitate the charge transfer betweenCE and electrolyte [106] as shown in Table 3 Choi et al[59] fabricated a CE composed graphene and multiwalledcarbon nanotube (MWCNT) by a CVD method The incor-poration of graphene in the MWCNT matrix can provideanother area for I

3

minus reduction and thereby the effectivelyenhanced electrocatalytic activity can be expected for thegrapheneMWCNTCEThe cell with the grapheneMWCNTdisplayed an excellent FF value of 07 and exhibited a PCEof 446 Li et al [60] prepared vertically aligned carbonnanotubes (VACNTs) on a freestanding graphene paper(GP) by CVD The direct deposition of VACNTs on highlyconductive GP can facilitate the ionic diffusion within thecomposite electrode and electrons transfer at CEelectrolyteinterface As a result the VACNTGPCE displayed higher FFand PCE of 064 and 605 respectively compared with pureGP and VACNTGP CE Compared to conventional CVDmethod of growing graphene film to the desired substrates


Table 3 Photovoltaic performance of the DSSCs based on various graphenecarbon material CEs


GMWNT FTO glass CVD IminusI3

minus N719 mdash 070 446 [59]VACNTGP GP paper CVD IminusI

3

minus N719 340 062 605 [60]GPMWNT FTO glass CVD IminusI

3

minus N719 mdash 070 300 [61]GG-CNT FTO glass Electrophoretic deposition IminusI

3

minus N719 4900 061 617 [26]Graphene-SWNT FTO glass Electrophoretic deposition IminusI

3

minus N719 1620lowast 057 517 [62]

OMC-GNS FTO glass Doctor-blade IminusI3

minus N719 6776 061 682 [63]GOMC FTO glass Doctor-blade IminusI

3

minus N719 332 063 638 [64]MWNTGNS FTO glass Doctor-blade IminusI

3

minus N719 110lowast 058 400 [65]

Graphene-CB FTO glass Doctor-blade IminusI3

minus N719 027lowast 057 599 [66]

MWNTGr-F FTO glass Dry spun IminusI3

minus N719 170lowast 063 755 [67]

CFGNP FTO glass Spin-coating Co3+Co2+ Y123 112 074 911 [68]GMC FTO glass Screen-printing T

2Tminus N719 126 069 655 [27]

GPMWNT FTO glass Spin-coating IminusI3

minus N719 294 053 466 [69]GRMWCNT FTO glass Spray IminusI

3

minus N719 1089lowast 049 770 [70]

NGC FTO glass Screen-printing IminusI3

minus N719 178 049 619 [71]lowastRepresents that the unit of the 119877ct value isΩ

Graphitepaper

Graphitepaper

RG-CNTssolution

V

(a)

RG

EPD

CNTs

RG-CNTscomposite film

(b)

Figure 5 (a) Schematic diagram of EPD process (b) Structure illustration of RG-CNTs composite films [26]

as CEs electrophoretic deposition (EPD) is a relativelyeconomical and versatilemethod to fabricate graphene-basedCEs since the thickness of graphene film can be controlledby adjusting the deposition parameters such as depositiontime and applied voltage As depicted in Figure 5 Zhu etal [26] used a facile EPD approach to prepare reducedgraphene (RG)CNT composite CEs Among the DSSCs withCNT RGCNT and Pt CEs RGCNT-based CE exhibited thehighest FF value and therefore achieved the impressive PCEThe improved FF value can be ascribed to the short pathwayof electron transfer within 2-D graphene sheets and theconstructed electrical network by connecting graphene sheetswith CNTs Kim et al [62] also used EPD method to depositthe graphene single-walled CNT (SWCNT) and graphene-SWCNT composite on FTO glass substrates Among themas-fabricated graphene-SWCNTCE not only exhibited excel-lent electrocatalytic activity but also displayed the opticaltransmittance of 67 at 550 nm On the other hand Ma et al[70] fabricated different transparent 3-D CNTgraphene CEsby controlling the spraying time and supportingwith amirror

to reharvest the reflected light The 30 transmittance ofcomposite showed the highest conversion efficiency (770)with a mirror for 119869sc increasing to 083mA cmminus2

In addition Miao et al [66] revealed highly electro-catalytic composite CEs based on the combination of therapid electron transport of graphene and high surface areaof carbon black The moderate bundles of graphene homo-geneously distributed within carbon black were observed forthe composite CE synthesized in the ratio of graphene andcarbon black in 1 3This would therefore provide some spacefor electrolyte diffusionThe improved electron transport andelectrolyte of the optimized composite CE would promotethe electrons transfer and provide more effective active sitesfor I3

minus reduction The DSSC based on the graphenecarbonblack showed a PCE of 599 On the other hand orderedmesoporous carbon (OMC) has attracted extensive attentionbecause of its great chemical stability fast infiltration ofelectrolyte effective catalysis area and large pore volume[107] However OMC with random boundaries usually haslow electron mobility and thus its electrocatalytic activity is


Graphene sheet

Mesoscopic carbon material

Modify

Graphene modified mesoscopic carbon material

ETminusNa+

BET

eminus

S S

SminusNa+N

N

N NN

NN

N

N N

N

N

Figure 6 Fabrication of graphene modified mesoscopic carbon (GMC) material toward a new synthesized thiolatedisulfide redox couple(ETminusBET) [27]

insufficient as CE material in DSSCs [64] To address theweakness of OMC Sun et al [64] combined OMC withhighly conductive reduced graphene oxide (RGO) to forma OMCRGO composite CE Therefore the device with theOMCRGO composite CE exhibited higher PCE of 638than that based on the OMC CE (567) More recentlyShao et al [63] prepared OMCgraphene nanosheet (GNS)composite with different weight ratios of GNS ranging from5 to 50wt The optimized OMCGNS composite CE with25wt GNS displayed the most excellent electrocatalyticactivity and yielded the highest PCE of 682 which rivaledthat of the cell with Pt CE (708)The improved photovoltaicperformance of the aforementioned OMCgraphene-basedcomposite CEs is mainly ascribed to the increased pathwayfor electron transfer by the introduction of highly conductivegraphene sheets

In addition to I3

minusIminus redox couple several graphenecarbonmaterials were employed as CEs for iodine-free DSSCsRecently Liursquos group [27] utilized graphene modified meso-scopic carbon (GMC) as CE in DSSCs with thiolatedisulfide(ETminusBET) mediator as illustrated in Figure 6 and obtainedsignificantly improved FF value in which the FF value ofmesoscopic carbon (NC) and GMC was 325 and 725respectively Thus remarkably enhanced PCE of 655 wasachieved for the GMC-based device which was much higherthan that of the NC-based one The EIS measurementsconfirmed that the119877ct value of GMCCEwas only 126Ω cm2which was almost ten times lower than that of NC CE(1287Ω cm2)The low 119877ct value of the GMCCE is accountedfor its low FF value As a result the GMC-based DSSCwith disulfide redox couple system exhibited a superior PCEwhich was increased by 35 than that of the GC-based oneAs for coupling with Co(bpy)

3

3+Co(bpy)3

2+ redox coupleStefik et al [68] developed a novel type of cathode composedof carbon fibers (CF) and graphene nanoplatelets (GNP)TheCFGNP composite CEwas fabricated by embedding GNP ina conductive carbon matrix derived from the carbonizationof poly(acrylonitrile) (PAN) This approach was found to

effectively improve the adhesion of GNP with the conductiveglass substrates After the optimization the CFGNP CEcontaining 20 GNP not only showed the lowest 119877ct valueof 112Ω cm2 but also displayed its stable mechanical strengthagainstmechanical aging testsTheDSSCswith the optimizedCFGNP CEs have the prominent PCE of 911 which washigher than that of the cell based on Pt CE (861)

5 GrapheneConducting Polymer Composites

Organic conducting polymers such as polyaniline (PANI)poly(34-ethylenedioxythiophene) (PEDOT) and polypyr-role (PPy) have also attracted lots of attention to be consid-ered as potential CE materials due to their desirable char-acteristics of low-cost environmental stability high degreeof processability and interesting electrocatalytic propertiesAs depicted in Table 4 to improve the electrocatalytic ofconducting polymers for I

3

minus reduction highly conductivegraphene are generally incorporated into the matrix ofconducting polymers to increase their electrical conductivityfor rapid electron transfer For example Hong et al [72]fabricated transparent graphenepolystyreneslufonate dopedpoly(34-ethylenedioxythiophene) (PEDOTndashPSS) compositefilms on conductive glass substrates by spin-coating the aque-ous mixture of 1-pyrenebutyrate (PBminus) stabilized grapheneand PEDOT-PSS The graphene sheets were observed tobe dispersed uniformly in PEDOT-PSS matrix and theresultant composite film possessed the combined advantagesof the excellent electrocatalytic PEDOT-PSS and the highconductive graphene The PCE of the device was increasedfrom 23 to 45 with increasing the content of grapheneincorporated in the composite film from 0wt to 1 wtMoreover Lee et al [73] used graphenePEDOT compositefilm to replace not only the Pt catalyst but also the transparentconducting oxide (TCO) layer in DSSCs The cell assembledwith such Pt- and TCO-free CE achieved a PCE of 626while the PCEs of DSSCs with PtITO and PEDOT CEswere 668 and 562 respectively Yue et al [74] prepared


Table 4 Photovoltaic performance of the DSSC using various grapheneconducting polymer CEs

CE Substrate Deposition Redox couple Dye 119877ct (Ω cm2) FF PCE () Ref

Graphene-PEDOT-PSS ITO glass Spin-coating IminusI

3

minus N719 mdash 048 450 [72]

GraphenePEDOT TCO glass Polymerization IminusI3

minus N719 mdash mdash 626 [73]

GPPEDOT-PSS FTO glass Electrochemicalpolymerization IminusI

3

minus N719 274 065 786 [74]

PANIgraphene FTO glass Electrodeposition IminusI3

minus N719 1149lowast 067 770 [75]

PANI-RGO FTO glassLayer-by-layerelectrostaticadsorptionmechanism

IminusI3

minus N719 071 064 784 [76]

PpyRGO ITO glasselectrochemical

Oxidativepolymerization

IminusI3

minus N719 3295lowast 060 645 [77]

PANIgraphene FTO glass Polymerization IminusI3


Adsorption ASP

ASP

Polymerization

Aniline Graphene sheetsPANIgraphene

PANI nanorods

Polymerization

Without graphenesheets

+

Figure 7 Schematic illumination for the synthesis of PANIgraphene hybrid [35]

graphenePEDOT-PSS composite film on FTO glass sub-strates using in situ electropolymerization approach inwhichthe different contents of graphene flakes were included inthe deposition bathThe as-deposited graphenePEDOT-PSScomposite film possessed a lot of clusters for providing theactive surface area and facilitating the penetration of theliquid electrolyte The incorporation of 005wt graphenewithin the PEDOT-PSS matrix resulted in the most improve-ment of the electrocatalytic activity for I

3

minus reduction TheDSSC based on such optimized graphenePEDOT-PSS CEshowed a high PCof 786 comparablewith the performanceof the DSSC using the Pt CE (731) In addition to PEDOTPANI and PPy conducting polymers have been hybrid withgraphene as efficient CEs in DSSCs

He et al [75] mixed PANI with graphene as PANIgra-phene composites via a refluxing process It was found thatPANI was bonded onto graphene without any interfacialseparation the resulting covalent bonding could improvethe electron transfer between PANI and graphene TheDSSC employing the PANI8wt graphene composite CEprovided an impressive PCE of 770 in comparison with640 from the pristine PANI CE-based device Wang et al[76] firstly incorporated GO into PANI matrix via layer-by-layer electrostatic adsorption method To further enhance

the electrical conductivity and electrocatalytic activity ofthe PANI-GO films they were reduced with hydroiodicacid in the form of PANI-RGO composite films They alsofound that the incorporation of RGO into PANI matrix canincrease the transparency of PANI and promote the light-harvesting from the rear side of devices A cell based on thetransparent PANI-RGO CE can achieve an impressive PCEof 784 which is comparable to that assembled with Pt CE(819) Liu et al [77] employed a facile two-step electro-chemical process to fabricate PPyRGO composites Firstlythe PPyGO composites were obtained by electrochemicaloxidative polymerization Secondly the GO incorporated inthe PPyGO composites was effectively reduced to RGOthrough cyclic voltammetry method to obtain PPyRGOcomposites After optimizing the polymerization period ofPPyGO the DSSC based on the optimized PPyRGO CEpresented a PCE of 645 which was ca 90 of that of thedevice using a thermally deposited Pt CE (714)

In addition to the mixture of graphene and conductingpolymers Wang et al [35] synthesized a hybrid material ofpolyaniline (PANI) nanoparticles dispersed on the grapheneprepared using an in situ polymerization method (Figure 7)In their work the graphene sheets function as highly con-ductive supports for decorating PANI nanoparticles thus


Table 5 Photovoltaic performance of the DSSC using various graphenemetal sulfide material CEs

CE Subtract Deposition Redox couple Dye 119877ct (Ω cm2) FF PCE () Ref

G-CoS FTO glass CVD + SILAR IminusI3

minus N719 505 036 342 [78]CoSgraphene FTO glass CVD + Dip-coating IminusI

3

minus N719 mdash 069 504 [78]NiSgraphene FTO glass CVD + Dip-coating IminusI

3

minus N719 860 070 525 [79]CoS2-G FTO glass Doctor-blade IminusI

3

minus N719 130 060 655 [80]NDGCoS FTO glass Spin-coating IminusI

3

minus N719 258lowast 074 1071 [81]

CSG FTO glass LBL IminusI3

minus N719 570lowast 063 543 [82]

FGNS FTO glass Electrophoretic deposition IminusI3

minus N719 179lowast 064 554 [83]

CoSRGO FTO glass Electrophoretic deposition + IED IminusI3

minus N719 359 063 939 [84]NiS2RGO FTO glass Drop-casting IminusI

3

minus N719 290 069 855 [85]GPNiS FTO glass Doctor-blade IminusI

3

minus N719 063lowast 068 767 [86]

NiS-G FTO glass Drop-casting IminusI3

minus N719 898lowast 062 826 [87]

MoS2RGO FTO glass Drop-casting IminusI

3

minus N719 057 066 604 [36]MoS2graphene FTO glass Doctor-blade IminusI

3

minus N719 217 068 598 [88]MoS2-GNS FTO glass Electrophoretic deposition IminusI

3

minus N719 234 059 581 [89]MoS2FG FTO glass Doctor-blade IminusI

3

minus N719 267 061 607 [90]MoS2RGO FTO glass Electrophoretic deposition IminusI

3

minus N719 517 067 746 [37]SnS2RGO FTO glass Doctor-blade IminusI

3

minus N719 724lowast 067 712 [91]

SnSRGO FTO glass Drop-casting IminusI3

minus N719 2312lowast 049 530 [92]

SnS2RGO FTO glass Drop-casting IminusI

3

minus N719 529lowast 062 747 [92]

Bi2S3-reduced graphene

oxide FTO glass Doctor-blade IminusI3

minus N719 920lowast 060 550 [93]

RGOCu2S FTO glass Doctor-blade IminusI

3

minus N719 324lowast 069 712 [94]

CIS-G FTO glass Doctor-blade IminusI3

minus N719 230lowast 061 640 [95]

CuInS2RGO FTO glass Doctor-blade IminusI

3

minus N719 065 051 618 [96]CZTSgraphene FTO glass Doctor-blade IminusI

3

minus N719 1333lowast 066 781 [38]


providing rapid electron transfer to highly electrocatalyticPANI nanoparticles and increased electrocatalytic activesites for the reduction of I

3

minus As a result the DSSC withPANIgraphene counter electrode achieved a PCE of 609which is comparable to that of the cell with Pt CE (688)

6 GrapheneInorganic Compound Composites

Except for conventional carbon materials and conductingpolymers great deals of studies have been recently reportedfor exploring low-cost highly efficient electrocatalytic mate-rials as CEs inDSSCs Up to date inorganic compounds suchas transitionmetal oxides nitrides sulfides and carbides [12ndash14 108ndash110] have demonstrated their promising potentialas Pt-free CEs because of their superior electrocatalyticactivity Nevertheless their electrical conductivity is stillinsufficient due to numerous defects or grain boundariesin their structures [16 81 111] To address this weaknessthe most efficient strategy is to hybridize nanostructuredinorganic compounds with highly conductive materials Asmentioned before graphene is one of the carbon familymaterials which can own outstanding electrical conduc-tivity for electron transfer between inorganic compoundsnanoparticles and high specific surface area for decorating

them Moreover the synthesis of nanostructured inorganiccompounds on graphene support could provide increasedelectrocatalytic sites for I

3

minus reduction The synergic effect ofthe aforementioned advantages of hybridization of grapheneand inorganic compounds nanoparticles would promote thecharge transfer between CEs and electrolyte In this sectionthe recent developments of the composite CEs composedof graphene and inorganic compounds are summarized inTables 5 and 6 and compared as follows

61 GrapheneMetal Sulfides In 2009 Wang et al [12] firstreported an electrochemical deposited cobalt sulfide (CoS)on ITOPEN film as an efficient CE in DSSCs Since thatvarieties of transition metal sulfides have been investigatedas CEs in DSSCs CE Among them molybdenum disul-fide (MoS

2) a typically two-dimensional layered stricture

exhibits Mo atoms bonding between the three stacked atomiclayers (SndashMondashS) by weak van der Waals interplay MoS

2

has two typical surfaces on the crystals which are terracesites on the basal planes and edge sites on the side surfacesDue to the anisotropic bonding and the general tendency tominimize the surface energy nanoparticles of layer materialsusually exhibit platelet-like morphology in which the basalplanes are exposed In addition the MoS

2proposed that the


Table 6 Photovoltaic performance of the DSSCs with various graphenemetal oxide material CEs


NiO-GP FTO glass Drop-casting IminusI3

minus N3 172 061 306 [97]NiO-NP-RGO FTO glass Dry plasma reduction IminusI

3

minus N719 1327 062 742 [98]GNSSiO

2FTO glass Dip-coating IminusI

3

minus N719 3980lowast 061 682 [99]

GNsZnO FTO glass Spin-coating IminusI3

minus N719 4 067 812 [100]Mn3O4RGO FTO glass Doctor-blade IminusI

3

minus N3 524lowast 061 590 [101]

La065

Sr035

MnO3RGO FTO glass Spin-coating IminusI

3

minus N719 071lowast 067 657 [102]

FeO3GFs FTO glass Screen-printing IminusI

3

minus N719 532lowast 068 745 [39]


20

15

10

5

00 20

13nm(Aring

)

(a) (b)

(c) (d)

Figure 8 Typical AFM images of (a) as-synthesized GO (b) RGOwith a low loading ofMoS2nanoparticles and (c) RGOwith a high loading

of MoS2nanoparticles The inset in (a) shows that the height difference between two red arrows is 13 nm (d) TEM image of the MoS

2RGO

nanocomposite [36]

catalytically active sites of MoS2lie on the edges of the typical

layered material but not on the basal planes [112] To pursueMoS2-based CEs with highly efficient performance inDSSCs

as depicted in Figure 8 our group first decorated MoS2

nanoparticles on reduced graphene oxide (RGO) surfaceand deposited the composites on FTO glass substrates asefficient CEs using drop-castingmethodThe extensive cyclicvoltammograms (CVs) showed that the cathodic current

density of the MoS2RGO CE was higher than that of MoS

2

RGO and sputtered Pt CEs due to the increased activesurface area of the former [36] As depicted in Figure 9 theenhanced electrocatalytic activity of the MoS

2RGO CE can

be attributed not only to the superior electrical conductivityof RGO but also to the considerable active surface area of theMoS2nanoparticles dispersed on the RGO surfaceTheDSSC

assembled with the MoS2RGO CE showed a comparable


eminus

eminus

2eminus

MoS2MoS2MoS2MoS2

MoS2 MoS2 MoS2

Iminus Iminus IminusI3

minus

(a)

eminus

eminus

eminus

MoS2

MoS2MoS2

MoS2

MoS2 MoS2

MoS2MoS2MoS2MoS2

MoS2

MoS2

FTO

(b)

Figure 9 Schematic of the catalytic mechanisms of (a) MoS2RGO and (b) MoS

2CEs [36]

(a) (b)

(c) (d)

Figure 10 FESEM images of (a) MoS2RGO and (b) MoS

2RGO-CNTs (c) TEM and (d) HRTEM images of MoS

2RGO-CNTs [37]

power conversion efficiency of 604 to the cell with a PtCE (638) Subsequently our group synthesized transparentMoS2graphene nanosheet (GNS) composites via one-pot

hydrothermal reaction and deposited themonFTOglass sub-strates using electrophoretic deposition The resultant trans-parent MoS

2GNS composite CE demonstrated both high

transmittance (gt70) at visible wavelengths and improvedelectrocatalytic activity The DSSC based on the transparent

CE still achieved an impassive PCE of 581 which is upto 93 of that obtained with the conventional Pt CE [89]The use of electrophoretic deposition has the advantages ofhigh deposition rate controlled thickness excellent unifor-mity large-scale production and being without any bindersRecently a hybrid of MoS

2RGO and CNTs (as depicted

in Figure 10) has been directly deposited onto FTO glasssubstrate by similar electrophoretic deposition and employed


as CE materials in DSSCs by our group [37] Electrochemicalstudies indicated that the incorporation of CNTs withinthe MoS

2RGO matrix can facilitate the electron transport

efficiently and therefore enhance the charge-transfer ratefor I3

minus reduction Consequently the DSSC assembled withthe MoS

2RGO-CNTs CE achieves an impressive PCE of

746 which is higher than that of devices that incorporateMoS2RGO CE (682) or Pt CE (723) [37]

Additionally Das et al [78] decorated CoS nanoparti-cles on graphene film (G-CoS) via successive ionic layeradsorption and reaction (SILAR) process therefore theincreased catalytic area for I

3

minus reduction at CEelectrolyteand CoS nanoparticles was obtained Consequently remark-ably improved FF and PCE values for the G-CoS based DSSCwere achieved compared to that with pristine CoS CE Biet al [79] synthesized two kinds of metal sulfides (CoS andNiS) and CoSgraphene and NiSgraphene composites as Pt-free CEs Firstly 3D graphene was directly deposited onSiO2substrate serving not only as conductivity layer for

electron transfer but also as support for decoratingCoS orNiSnanoparticles In recorded CV curves the cathodic currentdensities of CoSgraphene and NiSgraphene CEs were obvi-ously higher than those of CoSFTO NiSFTO and PtFTOindicating that the composites CEs have higher electrocat-alytic activity for I

3

minus reductionMoreover bothNiSgrapheneand CoSgraphene CEs showed the smaller 119877ct of 86 and88Ω cm2 than that of the NiSFTO (205Ω cm2) CoSFTO(264Ω cm2) and PtFTO (91Ω cm2) CEs signifying thesignificantly improved charge transfer at CEelectrolyte forthe NiSgraphene and CoSgraphene CEs The improvedPCE values of 525 and 504 were found for the DSSCsbased on the NiSgraphene and CoSgraphene CEs This canbe ascribed to their improved FF values of 072 and 069respectively More recently Duan et al [80] synthesized theCoS2graphene composite by a facile hydrothermal reaction

and utilized doctor-blade method to prepare CEs The incor-poration of graphene significantly controlled CoS

2particles

size and offered large reaction surface at CEelectrolyteTherefore CoS

2graphene composite CE could provide an

efficient diffusion channel for electrolyte penetration andenhanced electrocatalytic activity for I

3

minus reductionWhile theDSSC assembled with the CoS

2graphene composite CE it

displayed a PCE up to 655 which exceeded that of the Pt-based device (620)

Li et al [85] prepared the nanocomposites of NiS2

with reduced graphene oxide (NiS2RGO) by a facile

hydrothermal reaction Compared to RGO and NiS2CEs

the NiS2RGO exhibited superior electrocatalytic activity

Therefore the device with NiS2RGO CE exhibited a higher

PCE of 855 than that with RGO (314) or NiS2(702)

CE This can be explained by the fact that the NiS2RGO

CE possessed lower 119877ct value of 29Ω cm2 than that ofRGO (10002Ω cm2) and NiS

2(88Ω cm2) CEs therefore

revealing the faster charge transfer at CEelectrolyte Shenet al [87] used facile and low-temperature hydrothermalmethod to synthesize the nanocomposites composed of 1-DNiS and 2-D graphene (designated as NiS-G) with the ratioof grapheneNiS ranging from 02 to 06 Among all deviceswith NiS-G based CEs the DSSC based on the NiS-G04 CE

showed the highest 119869sc of 1705mA cmminus2 and PCE of 826which was much higher than that with pristine graphene(156) or NiS CE (741)The appropriate proportion of NiSand graphene could be associated with its morphology andthe diffusion resistance confirming that the loading of NiSfine rods can efficiently hinder the agglomeration of adjacentgraphene layers and favor the diffusion of the electrolytespecies within the NiS-G CE Yang et al [91] synthesized thenanocomposite composed of SnS

2nanoparticles and reduced

graphene oxide (designated as SnS2RGO) The 119877ct values

for Pt RGO SnS2 and SnS

2RGO are 2421 3420 3973

and 1796Ω respectively Compared with RGO and SnS2

SnS2RGO composite had the lower 119877ct value indicating its

higher electrocatalytic activity Moreover the DSSCs devicewith SnS

2RGO composite CE had a remarkable PCE of

712 which was significantly higher than SnS2CE (558)

and RGO CE (373) and even comparable to the valueof 679 obtained with a Pt reference CE The synergisticeffect between RGO and SnS

2showed both high electrical

conductivity and excellent electrocatalytic activity Zhou etal also synthesized CuInS

2and RGO by a facile method and

the resultant CuInS2RGO composite was directly employed

as CE material exhibit excellent electrocatalytic activity forthe triiodide reduction [95] The graphene-wrapped CuInS

2

composites were exploited as counter electrode for DSSCsand therefore achieved a power conversion efficiency of 64which is comparable to that of Pt CE (69) [95]

In addition to wrapping transitionmetal sulfide nanopar-ticles on graphene surface the graphene can be incorporatedinto metal sulfide matrix to serve the conductive networkin metal sulfides Huo et al [84] developed the sponge-likeCoSreduced graphene oxide (CoSRGO) by electrophoreticdeposition and ion exchange deposition The as-preparedpristine CoS as CE has a sponge-like morphology with largespecific surface area and low charge-transfer resistance atthe CEelectrolyte interface To further enhance the elec-trocatalytic activity of sponge-like CoS CEs the variouscontent of RGO was incorporated in the sponge-like CoSThe composite CE with the optimized composition ratio(CoSRGO

02 RGO 02mgLminus1) revealed the smallest 119877ct

value of 359Ω cm2 as well as the highest PCE of 939which was increased by 2793 compared with that usingPt CE Furthermore Bai et al [38] synthesized flower-likecopper zinc tin sulfide (CZTS) and graphene as compositeCE (Figure 11) The CZTSgraphene demonstrated excellentelectrocatalytic activity because the incorporation of highlyconductive graphene of 2 wt remarkably reduced its seriesresistance (119877s) from 2284Ω to 1333Ω and then enhancedthe electrical conductivity of the composite CE Liu et al[96] employed 3D CuInS

2microspheres as CE materials and

the DSSC based on the CE showed a PCE of only 331To improve the cell efficiency of the DSSC the CuInS

2

nanomaterial was hybridized with highly conductive RGOand its cell performance was increased to 618

62 GrapheneMetal Oxide Composites Bajpai et al [97]synthesized NiO nanoparticles homogeneously depositedover few-layered graphene platelets (GPs) by pulsed laserablation The device with NiO-GP CE yielded a PCE of


(a) (b)

(c) (d)

Figure 11 (a) and (b) SEM images of CZTSmicrospheresThe inset in (a) is HRTEM image of CZTS nanoparticle (c) SEM image of grapheneand (d) SEM image of annealed CZTSgraphene composites films [38]

306 which outperformed the cells using unsupportedNiO nanoparticles (203) or pristine GPs (246) and waseven comparable to a conventional Pt-based DSSC (357)Furthermore Dao et al [98] employed dry-plasma reductionto hybridize the NiO nanoparticles (NiO-NPs) on the surfaceof RGO The resultant NiO-NP-RGO CE displayed 119877ct valueof 193Ω cm2 much lower than that of NiO-NP-immobilizedCE (4439Ω cm2) and a GO-coated CE (1219Ω cm2) Inaddition the shunt resistant (119877h) value of the NiO-NP-RGOCE measured at a high frequency range was found to be244Ω cm2 which was slightly lower than the values foundfor RGO CE (245Ω cm2) and NiO-NP CE (253Ω cm2)This phenomenon can be associated with the decorationof NiO-NPs on the RGO surface which constructs lots ofbridges for facilitating electron transfer between NiO-CPsand RGO Gong et al [99] synthesized a porous graphene(GNS)SiO

2nanocomposite converted from graphene oxide

mixed with SiO2nanoparticles through facile hydrazine

hydrate reduction To substantiate the formation of poreswithin the composite film the GNSSiO

2nanocomposite

exhibited a narrow pore size distribution centered at 40 nmthus SiO

2nanoparticles played a significant role in the

GNS layers to build up porous nanostructured architectureCompared to SiO

2and GNS CEs the GNSSiO

2composite

CE demonstrated the lower 119877s and 119877ct values displaying itsfast electron and charge transfer Additionally the porousstructure of the GNSSiO

2composite film could provide

larger surface area than the GNS film thus enhancing theaccessibility of the electrolyte to the inside of CE and being

favorable for the reduction of I3

minus to Iminus As a consequenceDSSC assembled with GNSSiO

2CE achieved high cell

efficiency of 682 considered as a promising potentialcandidate to replace conventional Pt CE Recently Changet al [100] demonstrated that the combination of graphenenanosheets (GNS) and ZnO nanorods can be a highlyefficient 3-D CE in DSSCs The use of the ZnO nanorods as a3D framework nanostructure could prevent the aggregationsof GNs Unlike conventional chemical functionalization ofgraphene the electrocatalytic active sites are created by dam-aging the conjugated structure in the graphitic basal planwitha concomitant decrease in the electrical conductivity Thisnovel hybrid system has proved that the GNs were efficientlyisolated from each other to prevent the aggregation andrestacking of GNs which increased the active defective sitesfor the redox reaction of IminusI

3

minus to improve the electrocatalyticperformance Therefore the novel hybrid nanoarchitectureexhibited improved performance as a promising candidateCE for DSSCs due to the fast electron transport network andmore active sites for catalyzing the I

3

minus reductionThe PCE ofthe DSSC based on the GNsZnO nanorods CE was reached812 which was comparable to the device using Pt CE(882) Interestingly the inorganic transition metal oxidesFe2O3 exhibited approximately identical adsorption energy

of iodine compared to that of Pt in earlier research [113 114]Nevertheless the cells with Fe

2O3still obtained low overall

conversion efficiency due to the poor electron transportefficiency across Fe

2O3particles Yang et al [39] explored

Fe2O3nanoparticles (NPs) anchored onto 3D graphene


15

10

5

000 02 04 06 08

Voltage (V)

Curr

ent d

ensit

y (m

Ac

m2 )

PtFe2O3GFs

Fe2O3GFs

(a)

Curr

ent d

ensit

y (m

Ac

m2 )

2

1

0

minus1

minus2minus08 minus04 00 04 08

Epp Ox-1Ox-2

Red-2

Red-1

Voltage (V versus AgAg+)

PtFe2O3GFs

Fe2O3

GFs

(b)

20

15

10

5

010 15 20 25 30 35 40 45

minusZ998400998400

(Ω)

Z998400 (Ω)

2Rs

2Rct 2Zpore

NZ12CPE

PtFe2O3GFsFe2O3

GFs

(c)

Potential (V)

J(m

Ac

m2 )

10

1

01

001

1E minus 3

minus10 minus05 00 05 10

PtFe2O3GFs Fe2O3

GFs

(d)

Figure 12 (a) Current-voltage characteristics of the DSSCs with different CEs under one sun illumination (AM 15G) (b) Cyclicvoltammograms of various CEs for IminusI

3

minus redox species recorded at a scan rate of 50mV sminus1 Electrochemical impedance spectra (c) and(d) Tafel polarization curves of the symmetric dummy cells fabricated with different CEs (A colored version of this figure can be viewedonline [39])

frameworks (GFs) where Fe2O3NPs act as highly active

sites for reduction I3

minus and the 3D graphene frameworksform an interconnected electron transfer highway systemAs can be seen in Figure 12 The DSSCs fabricated with theFe2O3GFs CEs showed a higher PCE of 745 in comparison

to 729 for the DSSCs with Pt CEs [39] By EIS CVand Tafel polarization measurements (also summarized inFigure 12) 3D Fe

2O3GFs not only obtained high efficiency

but also provided multidimensional pathways to facilitatethe transport of electrons in the bulk electrode [39] Due tothe fast electron transfer in the interpenetrating grapheneframeworks the shuttle electrons easily cross the graphenesheets to the catalytic Fe

2O3NPs sites where the electrons

are used to reduce I3

minus Consequently Fe2O3NPs have lower

119877s and 119877ct to reduce the interface loss of charge transfer andenhance charge collection efficiency thereby boosting thephotovoltaic performance of DSSCs

63 Other Inorganic CompoundGraphene Composites Com-bination Ni

12P5and graphene (graphene-Ni

12P5) as a unique

composite CE also displayed interesting characteristics ofimproved electrocatalytic activity electrical conductivity andelectrolyte penetration [40] After evaluating the intrin-sic electrochemical features of the Ni

12P5 graphene and

graphene-Ni12P5asCEs inDSSCs the graphene-Ni

12P5com-

posite shows optimized electrochemical features includinglower charge-transfer resistance and diffusion impedanceby the combination of both contributions of the high


(a) (b)

(c) (d)

(e)0 2 4 6 8 10 12

(f)

Figure 13 Typical SEM ((a) and (b)) TEM ((c) and (d)) HRTEM (e) and EDS (f) images of mesoporous Ni085

SeRGO nanospheres [40]

electrocatalytic activity of Ni12P5nanocrystallites and fast

diffusion process of the electrolyte species in the grapheneThe main key could relative that the graphene-Ni

12P5com-

posite as CE had more active sites and spacers among thegraphene layers to accelerate the diffusion of electrolytespecies

On the other hand some studies have demonstrated thatNi085

Se presented excellent electrocatalytic performance forthe I3

minus reduction and can be a potential material as CEs[115] As can be seen in Figure 13 mesoporous Ni

085Se

nanospheres on reduced graphene oxide (Ni085

SeRGO)were further prepared because the mesoporous structureof Ni

085Se nanospheres and RGO both possessed large

specific surface area and fast electron transfer channels Con-sequently the Ni

085SeRGO CE could provide increased

catalytic active sites to reduce I3

minus and relatively fast electrontransfer channels thus significantly enhancing the electrocat-alytic activity of Ni

085SeRGO CE The PCE of the device

with theNi085

SeRGOCE reached 782 which was slightlyhigher than that of Pt CE (754)

In order to achieve the high-performance of DSSCswith CEs composed of inorganic compounds and carbonmaterials graphene sheets doped with heteroatoms such asnitrogen (N) boron (B) and phosphorous (P) can improvetheir electrocatalytic active sites [116] Therefore Balamu-rugan et al [117] hybridized iron nitride (FeN) core-shellnanoparticles grown on nitrogen-doped graphene (NG) asCEmaterial for application in DSSCs In particular the supe-rior performance of DSSCs with newly developed core-shellFeNNG nanohybrids was attributed to the high electrical


conductivity large surface area good surface hydrophilicityenhanced electrolyteCE interaction and excellent electro-catalytic activity toward the reduction of iodine redox speciesThe PCE of the DSSC with core-shell FeNNG CE reached1086 which was also superior to that of a cell with aconventional Pt CE (993) under the same experimentalconditions

7 Summary

DSSCs have been widely regarded as promising photovoltaicdevices to convert incident light to electricity In accordancewith the working mechanism of DSSCs CEs have to possessboth high electrical conductivity and excellent electrocat-alytic activity for collecting electron back from externalcircuit constructing rapid electron transfer network and cat-alyzing I

3

minus reduction reactionMoreover low-cost alternativeCEs should be explored to replace high-cost noble Pt CEfor large-scale applications As a result we review a greatdeal of graphene-based CE materials for low-cost Pt-freeDSSCs since graphene has the following specific propertiesof high electrical conductivity great anticorrosion resistanceand large surface area In this study the electrochemicalproperties of various graphene-based CEs and their effects oncell performance were systemically discussed It is found thatthe pristine graphene does not display sufficient electrocat-alytic activity due to its limited electroactive sites To improvethis issue three approaches have been conducted (i) thedecoration of excellent electrocatalytic nanomaterials on thesurface of highly conductive graphene (ii) the incorporationof graphene in the matrix of electrocatalytic materials toimprove its electrical conductivity and (iii) the introductionof highly conductive materials to connect graphene layers forpromoting electron transfer between them Although lots ofstudies have been carried out to improve the various aspectsof graphene-based CEs in DSSCs the device performance ofmost DSSCs is still relatively lower compared with that usinga conventional Pt CE

On the basis of strategies (i) and (iii) although thegraphene decorated with highly electrocatalytic nanoparti-cles has high electrocatalytic activity it still requires someconductive materials to connect graphene layers for pro-moting electron transfer Therefore the fabrication of thenovel hybrids composed of conductive materialsgraphenedecorated with highly electrocatalytic nanoparticles wouldbe a promising approach to design highly efficient Pt-freealternatives for low-cost DSSCs in the near future

Competing Interests

The authors declare that they have no competing interests

Acknowledgments

This research was supported by Ministry of Science andTechnology Taiwan (NSC 101-2221-M-036-035 and MOST103-2221-E-036-014-MY3)

References

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2filmsrdquo Nature vol

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[3] G Calogero A Bartolotta G Di Marco A Di Carlo andF Bonaccorso ldquoVegetable-based dye-sensitized solar cellsrdquoChemical Society Reviews vol 44 no 10 pp 3244ndash3294 2015

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[5] G Boschloo and A Hagfeldt ldquoCharacteristics of theiodidetriiodide redox mediator in dye-sensitized solarcellsrdquo Accounts of Chemical Research vol 42 no 11 pp1819ndash1826 2009

[6] MWu andTMa ldquoPlatinum-free catalysts as counter electrodesin dye-sensitized solar cellsrdquo ChemSusChem vol 5 no 8 pp1343ndash1357 2012

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[8] A Kanciurzewska E Dobruchowska A Baranzahi E Car-legrim M Fahlman and M A Gırtu ldquoStudy on poly(34-ethylene dioxythiophene)-poly(styrenesulfonate) as a plasticcounter electrode in dye sensitized solar cellsrdquo Journal ofOptoelectronics and Advanced Materials vol 9 no 4 pp 1052ndash1059 2007

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[10] J Xia N Masaki K Jiang and S Yanagida ldquoThe influence ofdoping ions on poly(34-ethylenedioxythiophene) as a counterelectrode of a dye-sensitized solar cellrdquo Journal of MaterialsChemistry vol 17 no 27 pp 2845ndash2850 2007

[11] Y Chen K S Kang K J Han K H Yoo and J Kim ldquoEnhancedoptical and electrical properties of PEDOT PSS films by theaddition ofMWCNT-sorbitolrdquo Synthetic Metals vol 159 no 17-18 pp 1701ndash1704 2009

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[13] Q W Jiang G R Li and X P Gao ldquoHighly ordered TiNnanotube arrays as counter electrodes for dye-sensitized solarcellsrdquo Chemical Communications no 44 pp 6720ndash6722 2009

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[15] G R Li J Song G L Pan and X P Gao ldquoHighly Pt-likeelectrocatalytic activity of transition metal nitrides for dye-sensitized solar cellsrdquo Energy and Environmental Science vol 4no 5 pp 1680ndash1683 2011

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2O3nanoparticles

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[71] J Ma C Li F Yu and J Chen ldquolsquoBrick-likersquo N-doped graphenecarbon nanotube structure forming three-dimensional filmsas high performance metal-free counter electrodes in dye-sensitized solar cellsrdquo Journal of Power Sources vol 273 pp1048ndash1055 2015

[72] WHong Y Xu G Lu C Li andG Shi ldquoTransparent graphenePEDOT-PSS composite films as counter electrodes of dye-sensitized solar cellsrdquo Electrochemistry Communications vol 10no 10 pp 1555ndash1558 2008

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[76] Y-S Wang S-M Li S-T Hsiao et al ldquoThickness-self-controlled synthesis of porous transparent polyaniline-reducedgraphene oxide composites towards advanced bifacial dye-sensitized solar cellsrdquo Journal of Power Sources vol 260 pp326ndash337 2014


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[79] H Bi W Zhao S Sun et al ldquoGraphene films decorated withmetal sulfide nanoparticles for use as counter electrodes of dye-sensitized solar cellsrdquo Carbon vol 61 pp 116ndash123 2013

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efficient catalytic counter electrode for dye-sensitized solar cellrdquoElectrochimica Acta vol 114 pp 173ndash179 2013

[81] E Bi H Chen X Yang W Peng M Gratzel and L HanldquoA quasi corendashshell nitrogen-doped graphenecobalt sulfideconductive catalyst for highly efficient dye-sensitized solarcellsrdquo Energy amp Environmental Science vol 7 no 8 pp 2637ndash2641 2014

[82] L Sun Y Bai N Zhang and K Sun ldquoThe facile preparationof a cobalt disulfide-reduced graphene oxide composite filmas an efficient counter electrode for dye-sensitized solar cellsrdquoChemical Communications vol 51 no 10 pp 1846ndash1849 2015

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[84] J Huo J Wu M Zheng Y Tu and Z Lan ldquoHigh per-formance sponge-like cobalt sulfidereduced graphene oxidehybrid counter electrode for dye-sensitized solar cellsrdquo Journalof Power Sources vol 293 pp 570ndash576 2015

[85] Z Li F Gong G Zhou and Z-S Wang ldquoNiS2reduced

graphene oxide nanocomposites for efficient dye-sensitizedsolar cellsrdquo The Journal of Physical Chemistry C vol 117 no 13pp 6561ndash6566 2013

[86] X Zuo R Zhang B Yang et al ldquoNiS nanoparticles anchoredon reduced graphene oxide to enhance the performance of dye-sensitized solar cellsrdquo Journal of Materials Science Materials inElectronics vol 26 no 10 pp 8176ndash8181 2015

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[88] G Yue J-Y Lin S-Y Tai Y Xiao and J Wu ldquoA catalyticcomposite film of MoS

2graphene flake as a counter electrode

for Pt-free dye-sensitized solar cellsrdquo Electrochimica Acta vol85 pp 162ndash168 2012

[89] J-Y Lin C-Y Chan and S-W Chou ldquoElectrophoretic deposi-tion of transparent MoS

2-graphene nanosheet composite films

as counter electrodes in dye-sensitized solar cellsrdquo ChemicalCommunications vol 49 no 14 pp 1440ndash1442 2013

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[91] B Yang X Zuo P Chen et al ldquoNanocomposite of tin sulfidenanoparticles with reduced graphene oxide in high-efficiencydye-sensitized solar cellsrdquo ACS Applied Materials amp Interfacesvol 7 no 1 pp 137ndash143 2015

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performance by introducing graphene in dye-sensitized solarcellsrdquo Electrochimica Acta vol 176 pp 797ndash803 2015

[93] G Li X Chen and G Gao ldquoBi2S3microspheres grown on

graphene sheets as low-cost counter-electrode materials fordye-sensitized solar cellsrdquo Nanoscale vol 6 no 6 pp 3283ndash3288 2014

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2S quantum dots as a transparent

counter electrode for dye sensitized solar cellsrdquo RSC Advancesvol 5 no 12 pp 9075ndash9078 2015

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composites for efficient dye-sensitized solar cellsrdquo FunctionalMaterials Letters vol 8 no 1 Article ID 1550011 2015

[96] M Liu G Li and X Chen ldquoOne-pot controlled synthesis ofspongelike CuInS

2microspheres for efficient counter electrode

with graphene assistance in dye-sensitized solar cellsrdquo ACSAppliedMaterials amp Interfaces vol 6 no 4 pp 2604ndash2610 2014

[97] R Bajpai S Roy N Koratkar and D S Misra ldquoNiO nanoparti-cles deposited on graphene platelets as a cost-effective counterelectrode in a dye sensitized solar cellrdquo Carbon vol 56 pp 56ndash63 2013

[98] V-D Dao L L Larina K-D Jung J-K Lee and H-S ChoildquoGraphenendashNiO nanohybrid prepared by dry plasma reductionas a low-cost counter electrode material for dye-sensitized solarcellsrdquo Nanoscale vol 6 no 1 pp 477ndash482 2014

[99] F Gong Z Li H Wang and Z-S Wang ldquoEnhanced electro-catalytic performance of graphene via incorporation of SiO

2

nanoparticles for dye-sensitized solar cellsrdquo Journal of MaterialsChemistry vol 22 no 33 pp 17321ndash17327 2012

[100] Q Chang Z Ma J Wang et al ldquoGraphene nanosheetsZnOnanorods as three-dimensional high efficient counter electrodesfor dye sensitized solar cellsrdquo Electrochimica Acta vol 151 pp459ndash466 2015

[101] Q Zhang Y Liu Y Duan et al ldquoMn3O4graphene composite as

counter electrode in dye-sensitized solar cellsrdquo RSC Advancesvol 4 no 29 pp 15091ndash15097 2014

[102] K Xiong G Li C Jin and S Jin ldquoLa065

Sr035

MnO3 RGO

nanocomposites as an effective counter electrode for dye-sensitized solar cellsrdquo Materials Letters vol 164 pp 609ndash6122016

[103] F Gong H Wang and Z-S Wang ldquoSelf-assembled monolayerof graphenePt as counter electrode for efficient dye-sensitizedsolar cellrdquo Physical Chemistry Chemical Physics vol 13 no 39pp 17676ndash17682 2011

[104] G Yue JWu Y Xiao et al ldquoPlatinumgraphene hybrid film as acounter electrode for dye-sensitized solar cellsrdquo ElectrochimicaActa vol 92 pp 64ndash70 2013

[105] K Saranya N Sivasankar and A Subramania ldquoMicrowave-assisted exfoliation method to develop platinum-decoratedgraphene nanosheets as a low cost counter electrode for dye-sensitized solar cellsrdquo RSC Advances vol 4 no 68 pp 36226ndash36233 2014

[106] C-T Hsieh B-H Yang and J-Y Lin ldquoOne- and two-dimensional carbon nanomaterials as counter electrodes fordye-sensitized solar cellsrdquo Carbon vol 49 no 9 pp 3092ndash30972011

[107] G Wang W Xing and S Zhuo ldquoApplication of mesoporouscarbon to counter electrode for dye-sensitized solar cellsrdquoJournal of Power Sources vol 194 no 1 pp 568ndash573 2009

[108] H Sun D Qin S Huang et al ldquoDye-sensitized solar cells withNiS counter electrodes electrodeposited by a potential reversal


techniquerdquo Energy amp Environmental Science vol 4 no 8 pp2630ndash2637 2011

[109] F Gong H Wang X Xu G Zhou and Z-S Wang ldquoIn situgrowth of Co

085Se and Ni

085Se on conductive substrates as

high-performance counter electrodes for dye-sensitized solarcellsrdquo Journal of the American Chemical Society vol 134 no 26pp 10953ndash10958 2012

[110] J S Jang D J Ham E Ramasamy J Lee and J S LeeldquoPlatinum-free tungsten carbides as an efficient counter elec-trode for dye sensitized solar cellsrdquo Chemical Communicationsvol 46 no 45 pp 8600ndash8602 2010

[111] G R Li F Wang J Song F Y Xiong and X P Gao ldquoTiN-conductive carbon black composite as counter electrode fordye-sensitized solar cellsrdquo Electrochimica Acta vol 65 pp 216ndash220 2012

[112] B Lei G R Li and X P Gao ldquoMorphology dependence ofmolybdenum disulfide transparent counter electrode in dye-sensitized solar cellsrdquo Journal of Materials Chemistry A vol 2no 11 pp 3919ndash3925 2014

[113] L J Brennan M T Byrne M Bari and Y K Gunrsquoko ldquoCarbonnanomaterials for dye-sensitized solar cell applications a brightfuturerdquo Advanced Energy Materials vol 1 no 4 pp 472ndash4852011

[114] S Das P Sudhagar V Verma et al ldquoAmplifying charge-transfercharacteristics of graphene for triiodide reduction in dye-sensitized solar cellsrdquo Advanced Functional Materials vol 21no 19 pp 3729ndash3736 2011

[115] X Zhang Y Yang S Guo F Hu and L Liu ldquoMesoporousNi085

Se nanospheres grown in situ on graphene with high per-formance in dye-sensitized solar cellsrdquo ACS Applied Materialsamp Interfaces vol 7 no 16 pp 8457ndash8464 2015

[116] D Yu E Nagelli F Du and L Dai ldquoMetal-free carbonnanomaterials becomemore active thanmetal catalysts and lastlongerrdquo The Journal of Physical Chemistry Letters vol 1 no 14pp 2165ndash2173 2010

[117] J Balamurugan T D Thanh N H Kim and J H LeeldquoNitrogen-doped graphene nanosheets with FeN core-shellnanoparticles as high-performance counter electrode materialsfor dye-sensitized solar cellsrdquo Advanced Materials Interfacesvol 3 no 1 Article ID 1500348 2016

Submit your manuscripts athttpwwwhindawicom

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CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research



MetallurgyJournal of


BioMed Research International

MaterialsJournal of


Nano

materials


Journal ofNanomaterials


Gla

ssFT

O

Gla

ssFT

OC

ount

er el

ectro

de

eminuseminus

Iminus

Iminus

Load

Redox couple

h

I3minus

I3minus

Iminusand I3minus

Figure 1 Schematic illustration of the operation principle of aDSSC

transfer as depicted in (4) After that the adsorbed Iminus ionsare desorbed from the CE surface to be the solvated Iminus ions inelectrolyte as illustrated in (5)

On the basis of the functions of a CE and the reductionmechanism of I

3

minus an efficient CE should exhibit both highelectrical conductivity and electrocatalytic activity to keep alow overpotential and to minimize energy loss in DSSCs [5]Generally Pt has been proven to be an excellent CE materialin DSSCs due to its high electrical conductivity and excellentelectrocatalytic activity as well as great electrochemical stabil-ity As a noble and sparse metal however the high cost of Pt(ca $50000Kg) restricts its practical applicationsThereforemuch effort has been devoted to exploring the efficient Pt-free CEs To date a great deal of materials including carbonmaterials [6] conducting polymers [7ndash11] and inorganicmaterials [12ndash18] have been introduced as alternative CEmaterials to Pt

Compared to other conventional carbon materials gra-phene a single-layer structure of two-dimensional graphitepossesses unique features of the strong mechanical strengthhigh electrical and thermal conductivity large surface areaand high optical transmittance [19] Therefore it has beenwidely incorporated in the fields ofmicroelectronic and opto-electronic devices energy storage and conversion materials[20 21] SinceAksayrsquos group revealed the functional graphenesheets (FGSs) as CE material for efficiently catalyzing theredox reaction of I

3

minusIminus in 2010 a variety of graphene-basedCE materials have been intensively developed for Pt-freeDSSCs [22]

In this work we comprehensively reviewed the advance ofresearch on graphene-based CE materials for Pt-free DSSCswith emphasis on composite materials

2 Graphene CEs

Graphene has been considered as one of the promising Pt-free CE alternatives in DSSCs due to its specific properties ofhigh electrical conductivity excellent electrocatalytic activitygreat anticorrosion resistance and larger surface area [24

28] In general graphene materials can be synthesized viamechanical exfoliation epitaxial growth chemical vapordeposition thermal exfoliation [29ndash32] and so forth Table 1summarizes the comparison of various graphene CEs inDSSCs For example Aksayrsquos group used thermal exfolia-tion to synthesize FGSs with defects and oxygen-containingfunction groups (hydroxyl carbonyl and epoxide) [24]Theyfound that the increase in CO ratio of FGSs is positivelyassociated with their electrocatalytic activity Neverthelessthe electrical conductivity of FGSs can be reduced by formingmore functional groups while the temperature of thermalprocessing increases over 1500∘C After the optimization ofCO ratio in FGSs the FGSs-basedDSSC reached higher PCEof 548 and fill factor (FF) of 060 than Pt-based DSSC(499 and 057) They found that the improved FF valueof the FGSs-based DSSC can be attributed to its relativelylow charge-transfer resistance (119877ct) of 064Ω cm

2 which iseven lower than that of the Pt CE (079Ω cm2) Gratzelrsquosgroup prepared an optically transparent graphene thin filmby dropping commercial graphene nanoplatelets on fluorinedoped tin oxide (FTO) glass substrates [23] They found thatthe graphene CE has amuch lower119877ct value in an ionic liquidthan in the traditional organic solvent by a factor of 5-6suggesting that the regeneration of I

3

minusIminus in an ionic liquid issuperior to that in the traditional organic solvent (as depictedin Figure 2) Choi et al [33] further prepared grapheneCEs using electrophoretic deposition followed by annealingtreatment at 200sim600∘C They found that the DSSC usingthe graphene CEs obtained after the annealing treatmentat 600∘C exhibited the optimized PCE of 569 Kaniyoorand Ramaprabhu [34] synthesized graphene with defect-rich and wrinkled structure through a thermally exfoliatedmethod Then the thermally exfoliated graphene (TEG)was suspended in Nafionethanol solution and subsequentlydropped on FTO glass substrates to form the TEG CEsThe TEG CE demonstrated 119877ct value of 117Ω cm2 whichis close to that of the Pt CE (65Ω cm2) This indicatesthat the wrinkled and defect-rich structure of TEG canprovide large surface area and high density of defect sidesfor I3

minusIminus reduction reaction and thus the electron transferkinetics at the CEelectrolyte interface is promoted Zhanget al synthesized novel 3D structure of graphene nanosheets(GNs) as CE material for DSSCs [28] The GN was preparedusing oxidative exfoliation of graphite followed by hydrazinereduction and annealing process After the optimizationof annealing temperature it can be found that the DSSCassembled with the GN CE annealed at 400∘C exhibitedthe best cell performance of 681 which is comparable tothat of the Pt-based DSSC (759) After being annealed at400∘C the GN was revealed with a unique 3D structureThissignifies that the annealed GN can afford sufficient surfacearea for I

3

minusIminus reduction reaction and therefore its 119877ct valueis significantly decreased from 3372 to 12Ω

On the other hand Xu et al [41] reported a facileand rapid microwave-assisted method to synthesize heminfunctionalized reduced graphene oxide (hemin-RGO) It wasfound that 5-layer hemin-RGO demonstrated 119877ct value ofca 7Ω comparable to that of the Pt-based CE (7Ω) Lee et






3


3

minus N719 3800lowast 065 569 [46]



3


3


3


3


3


3

minus N719 2000lowast 037 780 [34]




3


15

10

5

0

Curr

ent d

ensit

y (m

Ac

m2 )

00 02 04 06 08Voltage (V)

1 sun

05 sun

01 sun

Dark

PtZ946G3Z946

(a)

Curr

ent d

ensit

y (m

Ac

m2 )

1 sun

05 sun

01 sun

Dark

12

10

8

6

4

2

0

minus2

00 02 04 06 08Voltage (V)

PtZ952G3Z952

(b)








3

minus N3 236 059 291 [33]



3

minus N719 1045lowast 067 635 [52]



3


3


3


3


3

minus N719 265lowast 068 510 [58]



minus3Ωm2)


3





3


3


3

3+Co(bpy)3


3


3

3+Co(bpy)3


3

3+Co(bpy)3



3

3+Co(bpy)3


3

3+Co(bpy)3


3

3+Co(bpy)3


3

3+Co(bpy)3

2+






16

12

8

4

0


0 02 04 06 08Potential (V)

Phot

ocur

rent

den

sity

(mA

cm

2 )

(a)



10

8

6

4

2

0

Phot

ocur

rent

den

sity

(mA

cm


(b)


10

8

6

4

2

0


Phot

ocur

rent

den

sity

(mA

cm

2 )


(c)






2PtCl6and


20

18

16

14

12

10

8

6

4

2

000 01 02 03 04 05 06 07

GNGNPtNPs-20s-Pt

GNGNPtNPs-20s-Pt

120578 () Rct1 (Ω)

765 plusmn 012

879 plusmn 021

858 plusmn 015

Voc (V)

070 plusmn 002

069 plusmn 001

069 plusmn 001

(mA cmminus2) FF

1708 plusmn 041

1819 plusmn 058

1777 plusmn 037

064 plusmn 002

070 plusmn 001

070 plusmn 001

912

585

645

Cell voltage (V)

minus2 )

Phot

ocur

rent

den

sity

(mA

cm

JscCE





3







3


3


3


3

minus N719 1620lowast 057 517 [62]



3


3

minus N719 110lowast 058 400 [65]


minus N719 027lowast 057 599 [66]


minus N719 170lowast 063 755 [67]


2Tminus N719 126 069 655 [27]



3

minus N719 1089lowast 049 770 [70]



Graphitepaper

Graphitepaper

RG-CNTssolution

V

(a)

RG

EPD

CNTs


(b)







Graphene sheet


Modify


ETminusNa+

BET

eminus

S S

SminusNa+N

N

N NN

NN

N

N N

N

N



In addition to I3


3

3+Co(bpy)3





3






3

minus N719 mdash 048 450 [72]




3

minus N719 274 065 786 [74]


minus N719 1149lowast 067 770 [75]


IminusI3

minus N719 071 064 784 [76]



IminusI3

minus N719 3295lowast 060 645 [77]



Adsorption ASP

ASP

Polymerization


PANI nanorods

Polymerization


+



3










3


3


3


3

minus N719 258lowast 074 1071 [81]


minus N719 570lowast 063 543 [82]


minus N719 179lowast 064 554 [83]



3


3

minus N719 063lowast 068 767 [86]


minus N719 898lowast 062 826 [87]


3


3


3


3


3


3

minus N719 724lowast 067 712 [91]


minus N719 2312lowast 049 530 [92]


3

minus N719 529lowast 062 747 [92]



minus N719 920lowast 060 550 [93]


3

minus N719 324lowast 069 712 [94]


minus N719 230lowast 061 640 [95]


3


3

minus N719 1333lowast 066 781 [38]



3





3





2


2proposed that the






3

minus N719 1327 062 742 [98]GNSSiO


3

minus N719 3980lowast 061 682 [99]



3

minus N3 524lowast 061 590 [101]

La065

Sr035


3

minus N719 071lowast 067 657 [102]


3

minus N719 532lowast 068 745 [39]


20

15

10

5

00 20

13nm(Aring

)

(a) (b)

(c) (d)



2RGO

nanocomposite [36]






2


2RGO CE can




eminus

eminus

2eminus

MoS2MoS2MoS2MoS2

MoS2 MoS2 MoS2


minus

(a)

eminus

eminus

eminus

MoS2

MoS2MoS2

MoS2

MoS2 MoS2

MoS2MoS2MoS2MoS2

MoS2

MoS2

FTO

(b)


2CEs [36]

(a) (b)

(c) (d)



2RGO-CNTs [37]
















3



3



2particles




3


















2RGO are 2421 3420 3973












2







2




(a) (b)

(c) (d)






2nanocomposite





2composite








3


3








15

10

5

000 02 04 06 08

Voltage (V)

Curr

ent d

ensit

y (m

Ac

m2 )

PtFe2O3GFs

Fe2O3GFs

(a)

Curr

ent d

ensit

y (m

Ac

m2 )

2

1

0

minus1


Epp Ox-1Ox-2

Red-2

Red-1


PtFe2O3GFs

Fe2O3

GFs

(b)

20

15

10

5

010 15 20 25 30 35 40 45

minusZ998400998400

(Ω)

Z998400 (Ω)

2Rs

2Rct 2Zpore

NZ12CPE

PtFe2O3GFsFe2O3

GFs

(c)

Potential (V)

J(m

Ac

m2 )

10

1

01

001

1E minus 3


PtFe2O3GFs Fe2O3

GFs

(d)


3














12P5) as a unique


12P5 graphene and


12P5com-



(a) (b)

(c) (d)

(e)0 2 4 6 8 10 12

(f)





12P5com-





085Se









with theNi085





7 Summary


3



Competing Interests


Acknowledgments


References











































2ZnSnS




2O3nanoparticles


















































































2






Sr035

MnO3 RGO











085Se and Ni



















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials








3


3

minus N719 3800lowast 065 569 [46]



3


3


3


3


3


3

minus N719 2000lowast 037 780 [34]




3


15

10

5

0

Curr

ent d

ensit

y (m

Ac

m2 )

00 02 04 06 08Voltage (V)

1 sun

05 sun

01 sun

Dark

PtZ946G3Z946

(a)

Curr

ent d

ensit

y (m

Ac

m2 )

1 sun

05 sun

01 sun

Dark

12

10

8

6

4

2

0

minus2

00 02 04 06 08Voltage (V)

PtZ952G3Z952

(b)








3

minus N3 236 059 291 [33]



3

minus N719 1045lowast 067 635 [52]



3


3


3


3


3

minus N719 265lowast 068 510 [58]



minus3Ωm2)


3





3


3


3

3+Co(bpy)3


3


3

3+Co(bpy)3


3

3+Co(bpy)3



3

3+Co(bpy)3


3

3+Co(bpy)3


3

3+Co(bpy)3


3

3+Co(bpy)3

2+






16

12

8

4

0


0 02 04 06 08Potential (V)

Phot

ocur

rent

den

sity

(mA

cm

2 )

(a)



10

8

6

4

2

0

Phot

ocur

rent

den

sity

(mA

cm


(b)


10

8

6

4

2

0


Phot

ocur

rent

den

sity

(mA

cm

2 )


(c)






2PtCl6and


20

18

16

14

12

10

8

6

4

2

000 01 02 03 04 05 06 07

GNGNPtNPs-20s-Pt

GNGNPtNPs-20s-Pt

120578 () Rct1 (Ω)

765 plusmn 012

879 plusmn 021

858 plusmn 015

Voc (V)

070 plusmn 002

069 plusmn 001

069 plusmn 001

(mA cmminus2) FF

1708 plusmn 041

1819 plusmn 058

1777 plusmn 037

064 plusmn 002

070 plusmn 001

070 plusmn 001

912

585

645

Cell voltage (V)

minus2 )

Phot

ocur

rent

den

sity

(mA

cm

JscCE





3







3


3


3


3

minus N719 1620lowast 057 517 [62]



3


3

minus N719 110lowast 058 400 [65]


minus N719 027lowast 057 599 [66]


minus N719 170lowast 063 755 [67]


2Tminus N719 126 069 655 [27]



3

minus N719 1089lowast 049 770 [70]



Graphitepaper

Graphitepaper

RG-CNTssolution

V

(a)

RG

EPD

CNTs


(b)







Graphene sheet


Modify


ETminusNa+

BET

eminus

S S

SminusNa+N

N

N NN

NN

N

N N

N

N



In addition to I3


3

3+Co(bpy)3





3






3

minus N719 mdash 048 450 [72]




3

minus N719 274 065 786 [74]


minus N719 1149lowast 067 770 [75]


IminusI3

minus N719 071 064 784 [76]



IminusI3

minus N719 3295lowast 060 645 [77]



Adsorption ASP

ASP

Polymerization


PANI nanorods

Polymerization


+



3










3


3


3


3

minus N719 258lowast 074 1071 [81]


minus N719 570lowast 063 543 [82]


minus N719 179lowast 064 554 [83]



3


3

minus N719 063lowast 068 767 [86]


minus N719 898lowast 062 826 [87]


3


3


3


3


3


3

minus N719 724lowast 067 712 [91]


minus N719 2312lowast 049 530 [92]


3

minus N719 529lowast 062 747 [92]



minus N719 920lowast 060 550 [93]


3

minus N719 324lowast 069 712 [94]


minus N719 230lowast 061 640 [95]


3


3

minus N719 1333lowast 066 781 [38]



3





3





2


2proposed that the






3

minus N719 1327 062 742 [98]GNSSiO


3

minus N719 3980lowast 061 682 [99]



3

minus N3 524lowast 061 590 [101]

La065

Sr035


3

minus N719 071lowast 067 657 [102]


3

minus N719 532lowast 068 745 [39]


20

15

10

5

00 20

13nm(Aring

)

(a) (b)

(c) (d)



2RGO

nanocomposite [36]






2


2RGO CE can




eminus

eminus

2eminus

MoS2MoS2MoS2MoS2

MoS2 MoS2 MoS2


minus

(a)

eminus

eminus

eminus

MoS2

MoS2MoS2

MoS2

MoS2 MoS2

MoS2MoS2MoS2MoS2

MoS2

MoS2

FTO

(b)


2CEs [36]

(a) (b)

(c) (d)



2RGO-CNTs [37]
















3



3



2particles




3


















2RGO are 2421 3420 3973












2







2




(a) (b)

(c) (d)






2nanocomposite





2composite








3


3








15

10

5

000 02 04 06 08

Voltage (V)

Curr

ent d

ensit

y (m

Ac

m2 )

PtFe2O3GFs

Fe2O3GFs

(a)

Curr

ent d

ensit

y (m

Ac

m2 )

2

1

0

minus1


Epp Ox-1Ox-2

Red-2

Red-1


PtFe2O3GFs

Fe2O3

GFs

(b)

20

15

10

5

010 15 20 25 30 35 40 45

minusZ998400998400

(Ω)

Z998400 (Ω)

2Rs

2Rct 2Zpore

NZ12CPE

PtFe2O3GFsFe2O3

GFs

(c)

Potential (V)

J(m

Ac

m2 )

10

1

01

001

1E minus 3


PtFe2O3GFs Fe2O3

GFs

(d)


3














12P5) as a unique


12P5 graphene and


12P5com-



(a) (b)

(c) (d)

(e)0 2 4 6 8 10 12

(f)





12P5com-





085Se









with theNi085





7 Summary


3



Competing Interests


Acknowledgments


References











































2ZnSnS




2O3nanoparticles


















































































2






Sr035

MnO3 RGO











085Se and Ni



















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials







3

minus N3 236 059 291 [33]



3

minus N719 1045lowast 067 635 [52]



3


3


3


3


3

minus N719 265lowast 068 510 [58]



minus3Ωm2)


3





3


3


3

3+Co(bpy)3


3


3

3+Co(bpy)3


3

3+Co(bpy)3



3

3+Co(bpy)3


3

3+Co(bpy)3


3

3+Co(bpy)3


3

3+Co(bpy)3

2+






16

12

8

4

0


0 02 04 06 08Potential (V)

Phot

ocur

rent

den

sity

(mA

cm

2 )

(a)



10

8

6

4

2

0

Phot

ocur

rent

den

sity

(mA

cm


(b)


10

8

6

4

2

0


Phot

ocur

rent

den

sity

(mA

cm

2 )


(c)






2PtCl6and


20

18

16

14

12

10

8

6

4

2

000 01 02 03 04 05 06 07

GNGNPtNPs-20s-Pt

GNGNPtNPs-20s-Pt

120578 () Rct1 (Ω)

765 plusmn 012

879 plusmn 021

858 plusmn 015

Voc (V)

070 plusmn 002

069 plusmn 001

069 plusmn 001

(mA cmminus2) FF

1708 plusmn 041

1819 plusmn 058

1777 plusmn 037

064 plusmn 002

070 plusmn 001

070 plusmn 001

912

585

645

Cell voltage (V)

minus2 )

Phot

ocur

rent

den

sity

(mA

cm

JscCE





3







3


3


3


3

minus N719 1620lowast 057 517 [62]



3


3

minus N719 110lowast 058 400 [65]


minus N719 027lowast 057 599 [66]


minus N719 170lowast 063 755 [67]


2Tminus N719 126 069 655 [27]



3

minus N719 1089lowast 049 770 [70]



Graphitepaper

Graphitepaper

RG-CNTssolution

V

(a)

RG

EPD

CNTs


(b)







Graphene sheet


Modify


ETminusNa+

BET

eminus

S S

SminusNa+N

N

N NN

NN

N

N N

N

N



In addition to I3


3

3+Co(bpy)3





3






3

minus N719 mdash 048 450 [72]




3

minus N719 274 065 786 [74]


minus N719 1149lowast 067 770 [75]


IminusI3

minus N719 071 064 784 [76]



IminusI3

minus N719 3295lowast 060 645 [77]



Adsorption ASP

ASP

Polymerization


PANI nanorods

Polymerization


+



3










3


3


3


3

minus N719 258lowast 074 1071 [81]


minus N719 570lowast 063 543 [82]


minus N719 179lowast 064 554 [83]



3


3

minus N719 063lowast 068 767 [86]


minus N719 898lowast 062 826 [87]


3


3


3


3


3


3

minus N719 724lowast 067 712 [91]


minus N719 2312lowast 049 530 [92]


3

minus N719 529lowast 062 747 [92]



minus N719 920lowast 060 550 [93]


3

minus N719 324lowast 069 712 [94]


minus N719 230lowast 061 640 [95]


3


3

minus N719 1333lowast 066 781 [38]



3





3





2


2proposed that the






3

minus N719 1327 062 742 [98]GNSSiO


3

minus N719 3980lowast 061 682 [99]



3

minus N3 524lowast 061 590 [101]

La065

Sr035


3

minus N719 071lowast 067 657 [102]


3

minus N719 532lowast 068 745 [39]


20

15

10

5

00 20

13nm(Aring

)

(a) (b)

(c) (d)



2RGO

nanocomposite [36]






2


2RGO CE can




eminus

eminus

2eminus

MoS2MoS2MoS2MoS2

MoS2 MoS2 MoS2


minus

(a)

eminus

eminus

eminus

MoS2

MoS2MoS2

MoS2

MoS2 MoS2

MoS2MoS2MoS2MoS2

MoS2

MoS2

FTO

(b)


2CEs [36]

(a) (b)

(c) (d)



2RGO-CNTs [37]
















3



3



2particles




3


















2RGO are 2421 3420 3973












2







2




(a) (b)

(c) (d)






2nanocomposite





2composite








3


3








15

10

5

000 02 04 06 08

Voltage (V)

Curr

ent d

ensit

y (m

Ac

m2 )

PtFe2O3GFs

Fe2O3GFs

(a)

Curr

ent d

ensit

y (m

Ac

m2 )

2

1

0

minus1


Epp Ox-1Ox-2

Red-2

Red-1


PtFe2O3GFs

Fe2O3

GFs

(b)

20

15

10

5

010 15 20 25 30 35 40 45

minusZ998400998400

(Ω)

Z998400 (Ω)

2Rs

2Rct 2Zpore

NZ12CPE

PtFe2O3GFsFe2O3

GFs

(c)

Potential (V)

J(m

Ac

m2 )

10

1

01

001

1E minus 3


PtFe2O3GFs Fe2O3

GFs

(d)


3














12P5) as a unique


12P5 graphene and


12P5com-



(a) (b)

(c) (d)

(e)0 2 4 6 8 10 12

(f)





12P5com-





085Se









with theNi085





7 Summary


3



Competing Interests


Acknowledgments


References











































2ZnSnS




2O3nanoparticles


















































































2






Sr035

MnO3 RGO











085Se and Ni



















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials





16

12

8

4

0


0 02 04 06 08Potential (V)

Phot

ocur

rent

den

sity

(mA

cm

2 )

(a)



10

8

6

4

2

0

Phot

ocur

rent

den

sity

(mA

cm


(b)


10

8

6

4

2

0


Phot

ocur

rent

den

sity

(mA

cm

2 )


(c)






2PtCl6and


20

18

16

14

12

10

8

6

4

2

000 01 02 03 04 05 06 07

GNGNPtNPs-20s-Pt

GNGNPtNPs-20s-Pt

120578 () Rct1 (Ω)

765 plusmn 012

879 plusmn 021

858 plusmn 015

Voc (V)

070 plusmn 002

069 plusmn 001

069 plusmn 001

(mA cmminus2) FF

1708 plusmn 041

1819 plusmn 058

1777 plusmn 037

064 plusmn 002

070 plusmn 001

070 plusmn 001

912

585

645

Cell voltage (V)

minus2 )

Phot

ocur

rent

den

sity

(mA

cm

JscCE





3







3


3


3


3

minus N719 1620lowast 057 517 [62]



3


3

minus N719 110lowast 058 400 [65]


minus N719 027lowast 057 599 [66]


minus N719 170lowast 063 755 [67]


2Tminus N719 126 069 655 [27]



3

minus N719 1089lowast 049 770 [70]



Graphitepaper

Graphitepaper

RG-CNTssolution

V

(a)

RG

EPD

CNTs


(b)







Graphene sheet


Modify


ETminusNa+

BET

eminus

S S

SminusNa+N

N

N NN

NN

N

N N

N

N



In addition to I3


3

3+Co(bpy)3





3






3

minus N719 mdash 048 450 [72]




3

minus N719 274 065 786 [74]


minus N719 1149lowast 067 770 [75]


IminusI3

minus N719 071 064 784 [76]



IminusI3

minus N719 3295lowast 060 645 [77]



Adsorption ASP

ASP

Polymerization


PANI nanorods

Polymerization


+



3










3


3


3


3

minus N719 258lowast 074 1071 [81]


minus N719 570lowast 063 543 [82]


minus N719 179lowast 064 554 [83]



3


3

minus N719 063lowast 068 767 [86]


minus N719 898lowast 062 826 [87]


3


3


3


3


3


3

minus N719 724lowast 067 712 [91]


minus N719 2312lowast 049 530 [92]


3

minus N719 529lowast 062 747 [92]



minus N719 920lowast 060 550 [93]


3

minus N719 324lowast 069 712 [94]


minus N719 230lowast 061 640 [95]


3


3

minus N719 1333lowast 066 781 [38]



3





3





2


2proposed that the






3

minus N719 1327 062 742 [98]GNSSiO


3

minus N719 3980lowast 061 682 [99]



3

minus N3 524lowast 061 590 [101]

La065

Sr035


3

minus N719 071lowast 067 657 [102]


3

minus N719 532lowast 068 745 [39]


20

15

10

5

00 20

13nm(Aring

)

(a) (b)

(c) (d)



2RGO

nanocomposite [36]






2


2RGO CE can




eminus

eminus

2eminus

MoS2MoS2MoS2MoS2

MoS2 MoS2 MoS2


minus

(a)

eminus

eminus

eminus

MoS2

MoS2MoS2

MoS2

MoS2 MoS2

MoS2MoS2MoS2MoS2

MoS2

MoS2

FTO

(b)


2CEs [36]

(a) (b)

(c) (d)



2RGO-CNTs [37]
















3



3



2particles




3


















2RGO are 2421 3420 3973












2







2




(a) (b)

(c) (d)






2nanocomposite





2composite








3


3








15

10

5

000 02 04 06 08

Voltage (V)

Curr

ent d

ensit

y (m

Ac

m2 )

PtFe2O3GFs

Fe2O3GFs

(a)

Curr

ent d

ensit

y (m

Ac

m2 )

2

1

0

minus1


Epp Ox-1Ox-2

Red-2

Red-1


PtFe2O3GFs

Fe2O3

GFs

(b)

20

15

10

5

010 15 20 25 30 35 40 45

minusZ998400998400

(Ω)

Z998400 (Ω)

2Rs

2Rct 2Zpore

NZ12CPE

PtFe2O3GFsFe2O3

GFs

(c)

Potential (V)

J(m

Ac

m2 )

10

1

01

001

1E minus 3


PtFe2O3GFs Fe2O3

GFs

(d)


3














12P5) as a unique


12P5 graphene and


12P5com-



(a) (b)

(c) (d)

(e)0 2 4 6 8 10 12

(f)





12P5com-





085Se









with theNi085





7 Summary


3



Competing Interests


Acknowledgments


References











































2ZnSnS




2O3nanoparticles


















































































2






Sr035

MnO3 RGO











085Se and Ni



















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials





2PtCl6and


20

18

16

14

12

10

8

6

4

2

000 01 02 03 04 05 06 07

GNGNPtNPs-20s-Pt

GNGNPtNPs-20s-Pt

120578 () Rct1 (Ω)

765 plusmn 012

879 plusmn 021

858 plusmn 015

Voc (V)

070 plusmn 002

069 plusmn 001

069 plusmn 001

(mA cmminus2) FF

1708 plusmn 041

1819 plusmn 058

1777 plusmn 037

064 plusmn 002

070 plusmn 001

070 plusmn 001

912

585

645

Cell voltage (V)

minus2 )

Phot

ocur

rent

den

sity

(mA

cm

JscCE





3







3


3


3


3

minus N719 1620lowast 057 517 [62]



3


3

minus N719 110lowast 058 400 [65]


minus N719 027lowast 057 599 [66]


minus N719 170lowast 063 755 [67]


2Tminus N719 126 069 655 [27]



3

minus N719 1089lowast 049 770 [70]



Graphitepaper

Graphitepaper

RG-CNTssolution

V

(a)

RG

EPD

CNTs


(b)







Graphene sheet


Modify


ETminusNa+

BET

eminus

S S

SminusNa+N

N

N NN

NN

N

N N

N

N



In addition to I3


3

3+Co(bpy)3





3






3

minus N719 mdash 048 450 [72]




3

minus N719 274 065 786 [74]


minus N719 1149lowast 067 770 [75]


IminusI3

minus N719 071 064 784 [76]



IminusI3

minus N719 3295lowast 060 645 [77]



Adsorption ASP

ASP

Polymerization


PANI nanorods

Polymerization


+



3










3


3


3


3

minus N719 258lowast 074 1071 [81]


minus N719 570lowast 063 543 [82]


minus N719 179lowast 064 554 [83]



3


3

minus N719 063lowast 068 767 [86]


minus N719 898lowast 062 826 [87]


3


3


3


3


3


3

minus N719 724lowast 067 712 [91]


minus N719 2312lowast 049 530 [92]


3

minus N719 529lowast 062 747 [92]



minus N719 920lowast 060 550 [93]


3

minus N719 324lowast 069 712 [94]


minus N719 230lowast 061 640 [95]


3


3

minus N719 1333lowast 066 781 [38]



3





3





2


2proposed that the






3

minus N719 1327 062 742 [98]GNSSiO


3

minus N719 3980lowast 061 682 [99]



3

minus N3 524lowast 061 590 [101]

La065

Sr035


3

minus N719 071lowast 067 657 [102]


3

minus N719 532lowast 068 745 [39]


20

15

10

5

00 20

13nm(Aring

)

(a) (b)

(c) (d)



2RGO

nanocomposite [36]






2


2RGO CE can




eminus

eminus

2eminus

MoS2MoS2MoS2MoS2

MoS2 MoS2 MoS2


minus

(a)

eminus

eminus

eminus

MoS2

MoS2MoS2

MoS2

MoS2 MoS2

MoS2MoS2MoS2MoS2

MoS2

MoS2

FTO

(b)


2CEs [36]

(a) (b)

(c) (d)



2RGO-CNTs [37]
















3



3



2particles




3


















2RGO are 2421 3420 3973












2







2




(a) (b)

(c) (d)






2nanocomposite





2composite








3


3








15

10

5

000 02 04 06 08

Voltage (V)

Curr

ent d

ensit

y (m

Ac

m2 )

PtFe2O3GFs

Fe2O3GFs

(a)

Curr

ent d

ensit

y (m

Ac

m2 )

2

1

0

minus1


Epp Ox-1Ox-2

Red-2

Red-1


PtFe2O3GFs

Fe2O3

GFs

(b)

20

15

10

5

010 15 20 25 30 35 40 45

minusZ998400998400

(Ω)

Z998400 (Ω)

2Rs

2Rct 2Zpore

NZ12CPE

PtFe2O3GFsFe2O3

GFs

(c)

Potential (V)

J(m

Ac

m2 )

10

1

01

001

1E minus 3


PtFe2O3GFs Fe2O3

GFs

(d)


3














12P5) as a unique


12P5 graphene and


12P5com-



(a) (b)

(c) (d)

(e)0 2 4 6 8 10 12

(f)





12P5com-





085Se









with theNi085





7 Summary


3



Competing Interests


Acknowledgments


References











































2ZnSnS




2O3nanoparticles


















































































2






Sr035

MnO3 RGO











085Se and Ni



















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials








3


3


3


3

minus N719 1620lowast 057 517 [62]



3


3

minus N719 110lowast 058 400 [65]


minus N719 027lowast 057 599 [66]


minus N719 170lowast 063 755 [67]


2Tminus N719 126 069 655 [27]



3

minus N719 1089lowast 049 770 [70]



Graphitepaper

Graphitepaper

RG-CNTssolution

V

(a)

RG

EPD

CNTs


(b)







Graphene sheet


Modify


ETminusNa+

BET

eminus

S S

SminusNa+N

N

N NN

NN

N

N N

N

N



In addition to I3


3

3+Co(bpy)3





3






3

minus N719 mdash 048 450 [72]




3

minus N719 274 065 786 [74]


minus N719 1149lowast 067 770 [75]


IminusI3

minus N719 071 064 784 [76]



IminusI3

minus N719 3295lowast 060 645 [77]



Adsorption ASP

ASP

Polymerization


PANI nanorods

Polymerization


+



3










3


3


3


3

minus N719 258lowast 074 1071 [81]


minus N719 570lowast 063 543 [82]


minus N719 179lowast 064 554 [83]



3


3

minus N719 063lowast 068 767 [86]


minus N719 898lowast 062 826 [87]


3


3


3


3


3


3

minus N719 724lowast 067 712 [91]


minus N719 2312lowast 049 530 [92]


3

minus N719 529lowast 062 747 [92]



minus N719 920lowast 060 550 [93]


3

minus N719 324lowast 069 712 [94]


minus N719 230lowast 061 640 [95]


3


3

minus N719 1333lowast 066 781 [38]



3





3





2


2proposed that the






3

minus N719 1327 062 742 [98]GNSSiO


3

minus N719 3980lowast 061 682 [99]



3

minus N3 524lowast 061 590 [101]

La065

Sr035


3

minus N719 071lowast 067 657 [102]


3

minus N719 532lowast 068 745 [39]


20

15

10

5

00 20

13nm(Aring

)

(a) (b)

(c) (d)



2RGO

nanocomposite [36]






2


2RGO CE can




eminus

eminus

2eminus

MoS2MoS2MoS2MoS2

MoS2 MoS2 MoS2


minus

(a)

eminus

eminus

eminus

MoS2

MoS2MoS2

MoS2

MoS2 MoS2

MoS2MoS2MoS2MoS2

MoS2

MoS2

FTO

(b)


2CEs [36]

(a) (b)

(c) (d)



2RGO-CNTs [37]
















3



3



2particles




3


















2RGO are 2421 3420 3973












2







2




(a) (b)

(c) (d)






2nanocomposite





2composite








3


3








15

10

5

000 02 04 06 08

Voltage (V)

Curr

ent d

ensit

y (m

Ac

m2 )

PtFe2O3GFs

Fe2O3GFs

(a)

Curr

ent d

ensit

y (m

Ac

m2 )

2

1

0

minus1


Epp Ox-1Ox-2

Red-2

Red-1


PtFe2O3GFs

Fe2O3

GFs

(b)

20

15

10

5

010 15 20 25 30 35 40 45

minusZ998400998400

(Ω)

Z998400 (Ω)

2Rs

2Rct 2Zpore

NZ12CPE

PtFe2O3GFsFe2O3

GFs

(c)

Potential (V)

J(m

Ac

m2 )

10

1

01

001

1E minus 3


PtFe2O3GFs Fe2O3

GFs

(d)


3














12P5) as a unique


12P5 graphene and


12P5com-



(a) (b)

(c) (d)

(e)0 2 4 6 8 10 12

(f)





12P5com-





085Se









with theNi085





7 Summary


3



Competing Interests


Acknowledgments


References











































2ZnSnS




2O3nanoparticles


















































































2






Sr035

MnO3 RGO











085Se and Ni



















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




Graphene sheet


Modify


ETminusNa+

BET

eminus

S S

SminusNa+N

N

N NN

NN

N

N N

N

N



In addition to I3


3

3+Co(bpy)3





3






3

minus N719 mdash 048 450 [72]




3

minus N719 274 065 786 [74]


minus N719 1149lowast 067 770 [75]


IminusI3

minus N719 071 064 784 [76]



IminusI3

minus N719 3295lowast 060 645 [77]



Adsorption ASP

ASP

Polymerization


PANI nanorods

Polymerization


+



3










3


3


3


3

minus N719 258lowast 074 1071 [81]


minus N719 570lowast 063 543 [82]


minus N719 179lowast 064 554 [83]



3


3

minus N719 063lowast 068 767 [86]


minus N719 898lowast 062 826 [87]


3


3


3


3


3


3

minus N719 724lowast 067 712 [91]


minus N719 2312lowast 049 530 [92]


3

minus N719 529lowast 062 747 [92]



minus N719 920lowast 060 550 [93]


3

minus N719 324lowast 069 712 [94]


minus N719 230lowast 061 640 [95]


3


3

minus N719 1333lowast 066 781 [38]



3





3





2


2proposed that the






3

minus N719 1327 062 742 [98]GNSSiO


3

minus N719 3980lowast 061 682 [99]



3

minus N3 524lowast 061 590 [101]

La065

Sr035


3

minus N719 071lowast 067 657 [102]


3

minus N719 532lowast 068 745 [39]


20

15

10

5

00 20

13nm(Aring

)

(a) (b)

(c) (d)



2RGO

nanocomposite [36]






2


2RGO CE can




eminus

eminus

2eminus

MoS2MoS2MoS2MoS2

MoS2 MoS2 MoS2


minus

(a)

eminus

eminus

eminus

MoS2

MoS2MoS2

MoS2

MoS2 MoS2

MoS2MoS2MoS2MoS2

MoS2

MoS2

FTO

(b)


2CEs [36]

(a) (b)

(c) (d)



2RGO-CNTs [37]
















3



3



2particles




3


















2RGO are 2421 3420 3973












2







2




(a) (b)

(c) (d)






2nanocomposite





2composite








3


3








15

10

5

000 02 04 06 08

Voltage (V)

Curr

ent d

ensit

y (m

Ac

m2 )

PtFe2O3GFs

Fe2O3GFs

(a)

Curr

ent d

ensit

y (m

Ac

m2 )

2

1

0

minus1


Epp Ox-1Ox-2

Red-2

Red-1


PtFe2O3GFs

Fe2O3

GFs

(b)

20

15

10

5

010 15 20 25 30 35 40 45

minusZ998400998400

(Ω)

Z998400 (Ω)

2Rs

2Rct 2Zpore

NZ12CPE

PtFe2O3GFsFe2O3

GFs

(c)

Potential (V)

J(m

Ac

m2 )

10

1

01

001

1E minus 3


PtFe2O3GFs Fe2O3

GFs

(d)


3














12P5) as a unique


12P5 graphene and


12P5com-



(a) (b)

(c) (d)

(e)0 2 4 6 8 10 12

(f)





12P5com-





085Se









with theNi085





7 Summary


3



Competing Interests


Acknowledgments


References











































2ZnSnS




2O3nanoparticles


















































































2






Sr035

MnO3 RGO











085Se and Ni



















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials







3

minus N719 mdash 048 450 [72]




3

minus N719 274 065 786 [74]


minus N719 1149lowast 067 770 [75]


IminusI3

minus N719 071 064 784 [76]



IminusI3

minus N719 3295lowast 060 645 [77]



Adsorption ASP

ASP

Polymerization


PANI nanorods

Polymerization


+



3










3


3


3


3

minus N719 258lowast 074 1071 [81]


minus N719 570lowast 063 543 [82]


minus N719 179lowast 064 554 [83]



3


3

minus N719 063lowast 068 767 [86]


minus N719 898lowast 062 826 [87]


3


3


3


3


3


3

minus N719 724lowast 067 712 [91]


minus N719 2312lowast 049 530 [92]


3

minus N719 529lowast 062 747 [92]



minus N719 920lowast 060 550 [93]


3

minus N719 324lowast 069 712 [94]


minus N719 230lowast 061 640 [95]


3


3

minus N719 1333lowast 066 781 [38]



3





3





2


2proposed that the






3

minus N719 1327 062 742 [98]GNSSiO


3

minus N719 3980lowast 061 682 [99]



3

minus N3 524lowast 061 590 [101]

La065

Sr035


3

minus N719 071lowast 067 657 [102]


3

minus N719 532lowast 068 745 [39]


20

15

10

5

00 20

13nm(Aring

)

(a) (b)

(c) (d)



2RGO

nanocomposite [36]






2


2RGO CE can




eminus

eminus

2eminus

MoS2MoS2MoS2MoS2

MoS2 MoS2 MoS2


minus

(a)

eminus

eminus

eminus

MoS2

MoS2MoS2

MoS2

MoS2 MoS2

MoS2MoS2MoS2MoS2

MoS2

MoS2

FTO

(b)


2CEs [36]

(a) (b)

(c) (d)



2RGO-CNTs [37]
















3



3



2particles




3


















2RGO are 2421 3420 3973












2







2




(a) (b)

(c) (d)






2nanocomposite





2composite








3


3








15

10

5

000 02 04 06 08

Voltage (V)

Curr

ent d

ensit

y (m

Ac

m2 )

PtFe2O3GFs

Fe2O3GFs

(a)

Curr

ent d

ensit

y (m

Ac

m2 )

2

1

0

minus1


Epp Ox-1Ox-2

Red-2

Red-1


PtFe2O3GFs

Fe2O3

GFs

(b)

20

15

10

5

010 15 20 25 30 35 40 45

minusZ998400998400

(Ω)

Z998400 (Ω)

2Rs

2Rct 2Zpore

NZ12CPE

PtFe2O3GFsFe2O3

GFs

(c)

Potential (V)

J(m

Ac

m2 )

10

1

01

001

1E minus 3


PtFe2O3GFs Fe2O3

GFs

(d)


3














12P5) as a unique


12P5 graphene and


12P5com-



(a) (b)

(c) (d)

(e)0 2 4 6 8 10 12

(f)





12P5com-





085Se









with theNi085





7 Summary


3



Competing Interests


Acknowledgments


References











































2ZnSnS




2O3nanoparticles


















































































2






Sr035

MnO3 RGO











085Se and Ni



















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials








3


3


3


3

minus N719 258lowast 074 1071 [81]


minus N719 570lowast 063 543 [82]


minus N719 179lowast 064 554 [83]



3


3

minus N719 063lowast 068 767 [86]


minus N719 898lowast 062 826 [87]


3


3


3


3


3


3

minus N719 724lowast 067 712 [91]


minus N719 2312lowast 049 530 [92]


3

minus N719 529lowast 062 747 [92]



minus N719 920lowast 060 550 [93]


3

minus N719 324lowast 069 712 [94]


minus N719 230lowast 061 640 [95]


3


3

minus N719 1333lowast 066 781 [38]



3





3





2


2proposed that the






3

minus N719 1327 062 742 [98]GNSSiO


3

minus N719 3980lowast 061 682 [99]



3

minus N3 524lowast 061 590 [101]

La065

Sr035


3

minus N719 071lowast 067 657 [102]


3

minus N719 532lowast 068 745 [39]


20

15

10

5

00 20

13nm(Aring

)

(a) (b)

(c) (d)



2RGO

nanocomposite [36]






2


2RGO CE can




eminus

eminus

2eminus

MoS2MoS2MoS2MoS2

MoS2 MoS2 MoS2


minus

(a)

eminus

eminus

eminus

MoS2

MoS2MoS2

MoS2

MoS2 MoS2

MoS2MoS2MoS2MoS2

MoS2

MoS2

FTO

(b)


2CEs [36]

(a) (b)

(c) (d)



2RGO-CNTs [37]
















3



3



2particles




3


















2RGO are 2421 3420 3973












2







2




(a) (b)

(c) (d)






2nanocomposite





2composite








3


3








15

10

5

000 02 04 06 08

Voltage (V)

Curr

ent d

ensit

y (m

Ac

m2 )

PtFe2O3GFs

Fe2O3GFs

(a)

Curr

ent d

ensit

y (m

Ac

m2 )

2

1

0

minus1


Epp Ox-1Ox-2

Red-2

Red-1


PtFe2O3GFs

Fe2O3

GFs

(b)

20

15

10

5

010 15 20 25 30 35 40 45

minusZ998400998400

(Ω)

Z998400 (Ω)

2Rs

2Rct 2Zpore

NZ12CPE

PtFe2O3GFsFe2O3

GFs

(c)

Potential (V)

J(m

Ac

m2 )

10

1

01

001

1E minus 3


PtFe2O3GFs Fe2O3

GFs

(d)


3














12P5) as a unique


12P5 graphene and


12P5com-



(a) (b)

(c) (d)

(e)0 2 4 6 8 10 12

(f)





12P5com-





085Se









with theNi085





7 Summary


3



Competing Interests


Acknowledgments


References











































2ZnSnS




2O3nanoparticles


















































































2






Sr035

MnO3 RGO











085Se and Ni



















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials








3

minus N719 1327 062 742 [98]GNSSiO


3

minus N719 3980lowast 061 682 [99]



3

minus N3 524lowast 061 590 [101]

La065

Sr035


3

minus N719 071lowast 067 657 [102]


3

minus N719 532lowast 068 745 [39]


20

15

10

5

00 20

13nm(Aring

)

(a) (b)

(c) (d)



2RGO

nanocomposite [36]






2


2RGO CE can




eminus

eminus

2eminus

MoS2MoS2MoS2MoS2

MoS2 MoS2 MoS2


minus

(a)

eminus

eminus

eminus

MoS2

MoS2MoS2

MoS2

MoS2 MoS2

MoS2MoS2MoS2MoS2

MoS2

MoS2

FTO

(b)


2CEs [36]

(a) (b)

(c) (d)



2RGO-CNTs [37]
















3



3



2particles




3


















2RGO are 2421 3420 3973












2







2




(a) (b)

(c) (d)






2nanocomposite





2composite








3


3








15

10

5

000 02 04 06 08

Voltage (V)

Curr

ent d

ensit

y (m

Ac

m2 )

PtFe2O3GFs

Fe2O3GFs

(a)

Curr

ent d

ensit

y (m

Ac

m2 )

2

1

0

minus1


Epp Ox-1Ox-2

Red-2

Red-1


PtFe2O3GFs

Fe2O3

GFs

(b)

20

15

10

5

010 15 20 25 30 35 40 45

minusZ998400998400

(Ω)

Z998400 (Ω)

2Rs

2Rct 2Zpore

NZ12CPE

PtFe2O3GFsFe2O3

GFs

(c)

Potential (V)

J(m

Ac

m2 )

10

1

01

001

1E minus 3


PtFe2O3GFs Fe2O3

GFs

(d)


3














12P5) as a unique


12P5 graphene and


12P5com-



(a) (b)

(c) (d)

(e)0 2 4 6 8 10 12

(f)





12P5com-





085Se









with theNi085





7 Summary


3



Competing Interests


Acknowledgments


References











































2ZnSnS




2O3nanoparticles


















































































2






Sr035

MnO3 RGO











085Se and Ni



















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




eminus

eminus

2eminus

MoS2MoS2MoS2MoS2

MoS2 MoS2 MoS2


minus

(a)

eminus

eminus

eminus

MoS2

MoS2MoS2

MoS2

MoS2 MoS2

MoS2MoS2MoS2MoS2

MoS2

MoS2

FTO

(b)


2CEs [36]

(a) (b)

(c) (d)



2RGO-CNTs [37]
















3



3



2particles




3


















2RGO are 2421 3420 3973












2







2




(a) (b)

(c) (d)






2nanocomposite





2composite








3


3








15

10

5

000 02 04 06 08

Voltage (V)

Curr

ent d

ensit

y (m

Ac

m2 )

PtFe2O3GFs

Fe2O3GFs

(a)

Curr

ent d

ensit

y (m

Ac

m2 )

2

1

0

minus1


Epp Ox-1Ox-2

Red-2

Red-1


PtFe2O3GFs

Fe2O3

GFs

(b)

20

15

10

5

010 15 20 25 30 35 40 45

minusZ998400998400

(Ω)

Z998400 (Ω)

2Rs

2Rct 2Zpore

NZ12CPE

PtFe2O3GFsFe2O3

GFs

(c)

Potential (V)

J(m

Ac

m2 )

10

1

01

001

1E minus 3


PtFe2O3GFs Fe2O3

GFs

(d)


3














12P5) as a unique


12P5 graphene and


12P5com-



(a) (b)

(c) (d)

(e)0 2 4 6 8 10 12

(f)





12P5com-





085Se









with theNi085





7 Summary


3



Competing Interests


Acknowledgments


References











































2ZnSnS




2O3nanoparticles


















































































2






Sr035

MnO3 RGO











085Se and Ni



















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials











3



3



2particles




3


















2RGO are 2421 3420 3973












2







2




(a) (b)

(c) (d)






2nanocomposite





2composite








3


3








15

10

5

000 02 04 06 08

Voltage (V)

Curr

ent d

ensit

y (m

Ac

m2 )

PtFe2O3GFs

Fe2O3GFs

(a)

Curr

ent d

ensit

y (m

Ac

m2 )

2

1

0

minus1


Epp Ox-1Ox-2

Red-2

Red-1


PtFe2O3GFs

Fe2O3

GFs

(b)

20

15

10

5

010 15 20 25 30 35 40 45

minusZ998400998400

(Ω)

Z998400 (Ω)

2Rs

2Rct 2Zpore

NZ12CPE

PtFe2O3GFsFe2O3

GFs

(c)

Potential (V)

J(m

Ac

m2 )

10

1

01

001

1E minus 3


PtFe2O3GFs Fe2O3

GFs

(d)


3














12P5) as a unique


12P5 graphene and


12P5com-



(a) (b)

(c) (d)

(e)0 2 4 6 8 10 12

(f)





12P5com-





085Se









with theNi085





7 Summary


3



Competing Interests


Acknowledgments


References











































2ZnSnS




2O3nanoparticles


















































































2






Sr035

MnO3 RGO











085Se and Ni



















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




(a) (b)

(c) (d)






2nanocomposite





2composite








3


3








15

10

5

000 02 04 06 08

Voltage (V)

Curr

ent d

ensit

y (m

Ac

m2 )

PtFe2O3GFs

Fe2O3GFs

(a)

Curr

ent d

ensit

y (m

Ac

m2 )

2

1

0

minus1


Epp Ox-1Ox-2

Red-2

Red-1


PtFe2O3GFs

Fe2O3

GFs

(b)

20

15

10

5

010 15 20 25 30 35 40 45

minusZ998400998400

(Ω)

Z998400 (Ω)

2Rs

2Rct 2Zpore

NZ12CPE

PtFe2O3GFsFe2O3

GFs

(c)

Potential (V)

J(m

Ac

m2 )

10

1

01

001

1E minus 3


PtFe2O3GFs Fe2O3

GFs

(d)


3














12P5) as a unique


12P5 graphene and


12P5com-



(a) (b)

(c) (d)

(e)0 2 4 6 8 10 12

(f)





12P5com-





085Se









with theNi085





7 Summary


3



Competing Interests


Acknowledgments


References











































2ZnSnS




2O3nanoparticles


















































































2






Sr035

MnO3 RGO











085Se and Ni



















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




15

10

5

000 02 04 06 08

Voltage (V)

Curr

ent d

ensit

y (m

Ac

m2 )

PtFe2O3GFs

Fe2O3GFs

(a)

Curr

ent d

ensit

y (m

Ac

m2 )

2

1

0

minus1


Epp Ox-1Ox-2

Red-2

Red-1


PtFe2O3GFs

Fe2O3

GFs

(b)

20

15

10

5

010 15 20 25 30 35 40 45

minusZ998400998400

(Ω)

Z998400 (Ω)

2Rs

2Rct 2Zpore

NZ12CPE

PtFe2O3GFsFe2O3

GFs

(c)

Potential (V)

J(m

Ac

m2 )

10

1

01

001

1E minus 3


PtFe2O3GFs Fe2O3

GFs

(d)


3














12P5) as a unique


12P5 graphene and


12P5com-



(a) (b)

(c) (d)

(e)0 2 4 6 8 10 12

(f)





12P5com-





085Se









with theNi085





7 Summary


3



Competing Interests


Acknowledgments


References











































2ZnSnS




2O3nanoparticles


















































































2






Sr035

MnO3 RGO











085Se and Ni



















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




(a) (b)

(c) (d)

(e)0 2 4 6 8 10 12

(f)





12P5com-





085Se









with theNi085





7 Summary


3



Competing Interests


Acknowledgments


References











































2ZnSnS




2O3nanoparticles


















































































2






Sr035

MnO3 RGO











085Se and Ni



















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials





7 Summary


3



Competing Interests


Acknowledgments


References











































2ZnSnS




2O3nanoparticles


















































































2






Sr035

MnO3 RGO











085Se and Ni



















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials





























2ZnSnS




2O3nanoparticles


















































































2






Sr035

MnO3 RGO











085Se and Ni



















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials









































































2






Sr035

MnO3 RGO











085Se and Ni



















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials






085Se and Ni



















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials










CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials



review article recent development of graphene-based...

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