cu(i) based p-type metal oxide: a remarkably...

AbstractIn order to address the challenges in sustainable global development, considerable efforts

have been made to replace the conventional fossil fuels with the renewable resources of

energy, using photocatalysts and photo-electrochemical cells (PECs) by harvesting solar

energy. Here, we propose an efficient and commercially feasible solar water splitting using

Cuprous oxide (Cu2O) as photo-absorbing electrode material. Cu2O is an intrinsically p-

type semiconductor, with a direct band gap of 2.1 eV, making it one of the potential

semiconductors to be used for the photo-electrolysis of water for hydrogen generation.

However, it has a poor solar-to-hydrogen (STH) conversion efficiency because of the fast

recombination of electrons and holes, and weak stability in the aqueous medium. Here, we

describe an extensive study on the efficiency enhancement, while addressing the stability

of Cu2O against the photo-corrosion.

IntroductionHYDROGEN• Most abundant • High energy yield per mass• Environment friendly

U.S. Drive in partnership with U.S. DOE

Cu(I) METAL OXIDE:• Band gap : 2.0 - 2.1 eV• Proper Valence and Conduction band

edges at 1.43 V and -0.75 V • Abundant, non-toxic and low-cost• Theoretical photo-current density, Jp

= – 14.7 mA/cm2

• Theoretical ηSTH = 18%

Materials and MethodsChemicals required:Copper lactate solution, FTO substrates,ethanol, acetone, distilled water,KCl, NaOH, Na2SO4, HCl, H2SO4.

Instruments/ Set-up:Potentiostat - autolab, Xenonlight source (𝜆: 400 - 1100 nm),PEC cell, pH meter, thermometer.Electrodes:Pt wire, Ag/AgCl.

Methods:• Electrodeposition method for planar film deposition and fabrication• Hydrothermal method for Cu2O nanowires synthesis• Drop- casting method for film deposition of Cu2O nanowires• Effective pre-treatment of FTO substrates for enhancing stability

References1. Bak, T., Nowotny, J., Rekas, M., Sorrell, C.C., 2002. Photo-electrochemical hydrogen

generation from water using solar energy. Int. J. Hydrogen Energy 27, 991–1022.2. Dodds, P.E., Mcdowall, W., 2012. A review of hydrogen production technologies for energy

system models. UCL Energy Institute, Univ. Coll. London 1–22.3. Azevedo, J., Tilley, S.D., Schreier, M., Stefik, M., Sousa, C., Araujo, J.P., Mendes, A.,

Grätzel, M., Mayer, M.T., 2016. Tin oxide as stable protective layer for compositecuprous oxide water-splitting photocathodes. Nano energy, 10–16.

AcknowledgementAuthors would like to thank IITD for providing necessary lab facilities to carry out the experiments and characterizations.

Conclusions1. Planar Cu2O and nanowires of a resaonable aspect ratio were successfully synthesized2. Both the thin films were deposited on FTO substrates with an overall average

thicknesses of 4 µm3. A remarkably enhanced photocurrent density was achieved in the nanowires samples

from -0.15 mA/cm2 to – 3.19 mA/cm2 resulting into a more efficient solar water splitting

4. The stability of Cu2O thin film against photo-corrosion could be successfully prevented by the rigorous pre-treatment of FTO substrates using the oven-dry and nitrogen-dry methods

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Industrial SignificanceThe method of producing hydrogen as an alternative fuel by means of photo-

electrochemical water splitting is a completely environment friendly and cost-effective

procedure. The monolithic design of PEC using the low-cost semiconductor photocathode

material (Cu2O) and all operations at room temperature make it feasible to produce

hydrogen commercially.

Technology Readiness LevelThe set-up and all investigations so far have been done at the lab scale. After investigation

of hydrogen generation rate, the technology shall be upgraded to the pilot scale.

Cu(I) based p-type metal oxide: A remarkably efficient photo-

electrocatalyst for solar water splitting for hydrogen generation

Iqra Reyaz Hamdani, and Ashok N. Bhaskarwar*

Results

Industry Day Theme # 4: Sustainable Habitat

Fig.1 Principle of photo-assisted electrolysis

of water using photo-anode.

• Based on solar energy

• Environmentally safe

• Suitable for both small and

large scale

Fig.2 Photo-water splitting by Cu2O photocathode.

Fig.3 Electrodeposition of Cu2O from copper lactate solution.

U.S. Drive in partnership with U.S. DOE, 2016

Cu2O nanowires

drop

-0.60

-0.40

-0.20

0.00

0.20

0.40

-1.5 -1 -0.5 0

Ph

oto

cu

rre

nt

de

nsi

ty (m

A/c

m2 )

Voltage, V vs Ag/AgCl

-2.5

-2

-1.5

-1

-0.5

0

0 500 1000 1500 2000

Cu

rren

t (m

A)

Time of deposition (s)

-0.004

-0.002

0

0.002

0.004

-2 -1 0 1 2Cu

rre

nt

de

nsi

ty,

A/c

m2

Voltage, V vs Ag/AgCl

-0.006

-0.004

-0.002

0

0.002

0.004

0.006

0.008

-1.5 -1 -0.5 0 0.5 1 1.5

Cu

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/cm

2

Voltage, V vs Ag/AgCl

a) b) c)

d)

Fig. 4 a) TEM micrograph of Cu2O nanowires b) SEM micrograph of Cu2O nanowires c) Film

deposition on FTO by drop casting method d) Fabrication of Cu2O nanowires as photo-electrode.

V = -0.35V

Fig. 5 SEM micrograph of planar Cu2O. Fig. 6 a) i vs t response for electrodeposition of planar Cu2O

b) bare FTO substrate c) Cu2O film electrodeposited on FTO.

a) b) c)

Fig. 7 a) Film thickness of Cu2O nanowires: 4 µm b) film thickness of electrodeposited Cu2O: 3.9 µm,

using optical profilometer.

-40

-20

0

20

40

-1.5 -1 -0.5 0

Ph

oto

cu

rre

nt

de

nsi

ty (

10

-4A

/ cm

2)

Voltage, V vs Ag/AgCla)b)

Fig. 8 a) Photocurrent density of planar Cu2O: -0.15 mA/cm2 b) Photocurrent density of Cu2O

nanowires: -3.19 mA/cm2 at -1V vs Ag/AgCl.

a) b) c)

Fig. 9 a) Initial pre-treatment of FTO b) CV depicting instability of Cu2O film in aqueous medium

after 5th cycle c) Photographic image of unstable Cu2O photocathode.

a) b)

Fig. 10 a) Final pre-treatment

of FTO b) CV depicting good

stability of Cu2O thin film even

after 10th cycle.

a) b)