New Electrocatalysts For Fuel Cells

Principal Investigator: Philip N. Ross, Jr.Staff Scientist: Nenad Markovic1

Postdoctoral Fellows: Voja Stamenkovic1

Berislav Blizanac2

Materials Sciences DivisionLawrence Berkeley National Laboratory

Berkeley, CA 94720

Project ID #FC10This presentation does not contain any proprietary or confidential information

1Current address: Argonne National Laboratory2Current address: Cabot Superior Micropowders

2

Overview

• Total project funding– DOE share 100 %

• Funding for FY05:$ 500 K

• Funding for FY06:$ 253 K

BudgetBarriers

• Interactions/ collaborationsGeneral Motors Alternative

Power Center (GAPC)3M

Partners

• DOE Technical Barriers for Fuel Cell Components- Q. Electrode Performance

3

Objectives

• Reduce cost by reduction of precious metal loading (long term)

• Improve catalyst durability (long term)• Bring all ongoing work to a conclusion in

FY06• Publish all work in some form, i.e. either

archival literature or government reports

4

LBNL Materials-by-Design Approach

Model CatalystsPure Metals

AlloysSingle Crystals

Real CatalystsCarbon supported

pure metals or bimetallic

“Theory”

Surface Structuresvs.

KineticsReaction Mechanisms

Structure, composition and particle size

vs.Kinetics

Taylor made surfaces

Synthesis ofBimetallic Nanoparticles

PrototypeNew Catalyst

Test ing in Fuel Cells

Commercial Catalyst

5

Anticipated Gains with Pt Bimetallic Nanoparticles

Substitution of Pt atoms “buried” in interior of particlewith atoms of non-Pt group element atoms

Possibly higher activity for Pt surface atoms by electronicmodification from intermetallic bonding (alloying effect)

Norskov and Hammer theory correlates the position of d-band center toHad and Oad adsorption energies

Pt loading reduced (without any loss of performance)by a factor of 4 –5 seems possible

6

Outline of Presentation

Putting the finishing touches on the following topics:

• Skin vs.skeleton near-surface structures and the relation to kineticsfor the oxygen reduction reaction (ORR)

• Understanding the effect of subsurface transition metal atomson the activity of Pt3TM surfaces for the ORR – Norskov and Hammertheory of d-band center as measure of electronic effect of subsurfacetransition metal atoms on heat of adsorption of intermediates

New Results with Pt3Ni(hkl) single crystals point to newopportunities to improve intrinsic activity via control of nanoparticle shape

7

Summary: Near-surface characterization of Pt3TMdN

(E)/d

E /

arb.

uni

ts

a)

Pt251

Pt 237

Pt390

Auger electron energy / eV200 400 600 800

dN(E

)/dE

/ ar

b. u

nits

Pt 158Co 775

Co 716

Co 656

Pt 251

AES

Pt3Co Annealed

Pt3Co Sputtered

AES: absence of carbon and oxygen, Pt enrichment after annealing

UPS: d – band center position sputtered: 2.74 eV

annealed: 2.86 eV

14 12 10 8 6 4 2 0 -2

Pt3Co Annealed 2.86 eV Pt3Co Sputtered 2.74 eV

Inte

nsity

(Arb

. Uni

t)Binding Energy (eV)

LEISS: surface composition sputtered: Pt –75%, Co – 25%

annealed: Pt –100% Pt ‘skin’

E / E0

0.4 0.6 0.8

Inte

nsity

/ ar

b.un

itsIn

tens

ity /

arb.

units

Pt3Co Annealed

b)

Ni 0.37

Pt 0.71

LEISS

Pt3Co Sputtered

Top View

Top View

Pt

CoCo

Pt - skin

8

UHV: Before Transfer

AES3 keV

E/E0

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

Inte

nsity

[a.u

.]

0

10

20

30

40

LEISS1 keVNe+

PtCo

Pt

Co780

Co720

Co657

1° UHV

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

0

5

10

15

20

25

Y Ax

is T

itle

X axis title

PtCoLEISS1 keVNe+

UHV: After Rinsing with H2O

AES

3 keV

PtCo780

Co720

Co657

O5202° UHV

H2O rinsing

Summary: Stability of Pt3TM

1

Summary: Stability of Pt3TMUHV: Before Transfer

AES3 keV

Pt

Co780

Co720

Co657

E/E0

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

Inte

nsity

[a.u

.]

0

10

20

30

40

LEIS1 keVNe+PtCo

E/E0

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

Inte

nsity

[a.u

.]

0

5

10

15

20

25

LEIS1 keVNe+

Pt

Co

1° UHV

UHV: After rinsing with 0.1M HClO4and/or After Electrochem. Exp.

AES

3 keV

Pt

Co780

Co720

Co657

O520

C271

2° UHV

Co leaching out from the surface layers and formation of a Pt “skeleton” structure

0.1M HClO4 rinsing

2

Pt3VPt3Ti Pt3Fe Pt3Co Pt3Ni Pt-poly0.0

5.0

10.0

15.0

20.0

Kin

etic

Cur

rent

Den

sity

[mA

/cm

2]

skinskin

skel

eton

skel

eton

skin

skel

eton

@ 0.85 VRHE

skel

eton

skel

eton

3.03 eV3.37 eV

2.94 eV3.20 eV

2.89 eV3.05 eV

2.74 eV2.86 eV

2.69 eV2.72 eV

2.53 eV2.54 eV

SputteredAnnealed

d-band center [eV]2.63.03.4

Cur

rent

Den

sity

[mA

/cm

2 real

]

0

5

10

15

20

25

Pt3TiPt3V

Pt3Fe Pt3Co

Pt3Ni

Pt-poly

Annealed Surfaces

(1−Θad) term

ΔGad termand

(1−Θad) term

Summary: ORR activity vs. d-band center Pt3TM

3

ORR activity vs. d-band center: Pt3TMannealed(skin) vs sputtered(skeleton) surfaces

d-band center [eV]2.63.03.4

Cur

rent

Den

sity

[mA

/cm

2 real

]

0

5

10

15

20

25

Pt3Ti

Pt3V

Pt3Fe

Pt3Co

Pt3Ni

Pt-polyAnnealedSputtered

4

Summary: Skin vs. Skeleton near-surface structure

Blocking species are less adsorbed on Pt-skin, kinetics determined by (1-Θ) term

Complete segregation of Pt over Pt3M surfaces after annealing in UHV

Alloying components are dissolved instantaneously from the surfacein contact with acid electrolyte. Pt-skeleton surface is formed

Possible to create two different surfaces in UHV: Pt-skin and Pt3M

Only Pt atoms over Pt3(Co, Ni, Fe)

75% Pt and 25% M

Pt-skin, Pt-skeleton and Pt-poly have the same surface composition but different electronic properties || Pt-skin has protective role

Different position of d-band center provides different adsorption properties

1.

2.

3.

4.

6.

7.

The same/similar Tafel slope, activation energy, peroxide production → ORR pathway5.

With decrease of atomic number, d-band center shift increases, kinetics determined by both (1-Θ) term and ΔGad term

5

[011]

[01-1]

[1-10]

[001]

Pt3Ni(hkl): Surface Characterization | LEEDPt3Ni(100)

(5x1) superstructure

Pt3Ni(110)

c(4x2) superstructure

[1-10]

[001] Pt3Ni(110) c(4x2)

Pt3Ni(110) c(4x2)

Pt3Ni(111)

-Does not have a superstructure

-p(1x1)

-c(4x2) superstructure with different arrangement of surface atoms

-Different possible compositions

Pt3Ni(110) c(4x2) missing row

Pt3Ni(110)

Pt

Ni

47 eV

45 eV

6

Pt3Ni(hkl): Surface Characterization

E/E0

0.2 0.4 0.6 0.8

Inte

nsity

[arb

. uni

ts]

Annealed Sputtered

Ni 0.32

Pt 0.71

LEIS Ne+ 1 keV

Pt3Ni(100)

100%Pt 75%Pt 25%Ni

E/E0

0.2 0.4 0.6 0.8

Annealed Sputtered

LEIS Ne+ 1 keV

Ni 0.32

Pt 0.71

Pt3Ni(110)

100% Pt 75%Pt 25%Ni

E/E0

0.2 0.4 0.6 0.8

Inte

nsity

[arb

. uni

ts]

Ni 0.32Pt 0.71

LEIS Ne+ 1 keV

Pt3Ni(111)

Annealed Sputtered

100%Pt 75%Pt 25%Ni

LEISS:

-Complete Pt enrichment on the annealed Pt3Ni(hkl) surfaces

Pt3Ni(110) c(4x2)

7

Pt3Ni(100): EC Characterization

Pt(100) | Pt3Ni(100)

7.1 ± 0.7Ik @ 0.850V :

≈ 4.1Ik @ 0.875V :

≈ 2.2Ik @ 0.900V :

≈1.0Ik @ 0.925V :

3 ± 0.3

≈ 1.7

≈ 0.9

≈ 0.5

Ik @ 0.950V : ≈ 0.3≈ 0.2

Pt Pt3Ni Pt3Co

0.1M HClO4

i k [m

Acm

-2]

2

4

6

8

10

12

14Pt(100)Pt3Ni(100)

60oC

0.950 0.925 0.900 0.875 0.850 E [V] vs RHE

Activity Improvement Factor: 2.3

E [V] vs. RHE0.0 0.2 0.4 0.6 0.8 1.0 1.2

i [μA

/cm

2 ]

-20

0

20 Pt(100)

0.1M HClO4

20oC

E [V] vs. RHE0.0 0.2 0.4 0.6 0.8 1.0 1.2

i [μA

/cm

2 ]

-20

0

20 Pt(100)

Pt3Ni(100)

0.1M HClO4

20oC190

270

Hupd[μC/cm2]

Pt(100):

Pt3Ni(100):

8

Pt3Ni(110): EC Characterization

Pt(110) | Pt3Ni(110)

23 ± 2Ik @ 0.850V :

≈ 10.7Ik @ 0.875V :

≈ 5.1Ik @ 0.900V :

≈ 1.9Ik @ 0.925V :

11.5 ± 1

≈ 5.0

≈ 2.2

≈ 0.7

Ik @ 0.950V : ≈ 0.7≈ 0.2

0.1M HClO4

i k [m

Acm

-2]

5

10

15

20Pt(110)Pt3Ni(110)

60oC

0.950 0.925 0.900 0.875 0.850 E [V] vs RHE

Activity Improvement Factor: 2.1

E [V] vs. RHE0.0 0.2 0.4 0.6 0.8 1.0 1.2

i [μA

/cm

2 ]

-20

0

20Pt(110)

0.1M HClO4

20oC

E [V] vs. RHE0.0 0.2 0.4 0.6 0.8 1.0 1.2

i [μA

/cm

2 ]

-20

0

20Pt(110)

Pt3Ni(110)

0.1M HClO4

20oC194

208

Hupd[μC/cm2]

Pt(110):

Pt3Ni(110):

Oxide reduction

9

Pt3Ni(111): EC Characterization

Pt(111) | Pt3Ni(111)

(108 ± 10)Ik @ 0.850V :

≈ 46Ik @ 0.875V :

≈ 18Ik @ 0.900V :

≈ 5.7Ik @ 0.925V :

9 ± 1

≈ 4.4

≈ 1.9

≈ 0.8

Ik @ 0.950V : ≈ 1.7≈ 0.3

0.1M HClO4

i k [m

Acm

-2]

10

20

30

40 Pt(111)Pt3Ni(111)

60oC

0.950 0.925 0.900 0.875 0.850 E [V] vs RHE

Activity Improvement Factor: > 10

E [V] vs. RHE0.0 0.2 0.4 0.6 0.8 1.0 1.2

i [μA

/cm

2 ]

-20

0

20Pt(111)

0.1M HClO4

20oC

E [V] vs. RHE0.0 0.2 0.4 0.6 0.8 1.0 1.2

i [μA

/cm

2 ]

-20

0

20Pt(111)

Pt3Ni(111)

0.1M HClO4

20oC71

142

Hupd[μC/cm2]

Pt(111):

Pt3Ni(111):

10

10 8 6 4 2 0 -2

Pt (100)

Inte

nsity

(Arb

. Uni

t)

Binding Energy (eV)

Pt3Ni (100)

10 8 6 4 2 0 -2

Pt (110)

Inte

nsity

( A

rb. U

nit)

Binding Energy (eV)

Pt3Ni (110)

10 8 6 4 2 0 -2

Pt (111)

Inte

nsity

( A

rb. U

nit)

Binding Energy (eV)

Pt3Ni (111)

Pt (100) Pt3Ni(100)

d-band center

2.90 eV 3.14 eV

Δ d-band 0.24 eV

Pt (110) Pt3Ni(110)

d-band center

2.70 eV 2.53 eV

Δd-band -0.17 eV

Pt (111) Pt3Ni(111)

d-band center

2.76 eV 3.09 eV

Δ d-band 0.33 eV

Pt3Ni(hkl): UPS Characterization

11

Pt3Ni(111): ORR Activity

ik [mA/cm2]0.01 0.1 1 10 100 1000

E [V

] vs.

RH

E

0.84

0.88

0.92

0.96

1.00 36 mV/dec

54 mV/dec

Pt3Ni(111)

0.1 HClO4

60oC

45 mV/dec

64 mV/dec

69 mV/dec

53 mV/dec

Pt(111)

0.1 HClO4

60oCPt(111)

E [V] vs. RHE

0.0 0.2 0.4 0.6 0.8 1.0

i [m

A/c

m2 ]

-6

-4

-2

0Pt3Ni(111)

0.1 HClO4

60oC1600 rpm

IIIIII

1600 rpm

Pt(111)

Pt3Ni(111)

12

Publications and Presentations

Journal Publications

Mayrhofer, K., B. Blizanac, M. Arenz, V. Stamenkovic, P. Ross, N. Markovic, “The impact of geometric and surface electronic properties of Pt-nanocatalysts on the particle size effect in electrocatalysis”, J. Phys. Chem. B 109, 14433 JUL 13 2005.

Mayrhofer, K., B. Blizanac, M. Arenz, V. Stamenkovic, P. Ross, N. Markovic, “CO surface electrochemistry on Pt-nanoparticles: A selective review”, Electrochimica Acta 50, 5144 JUL 1 2005.

Arenz M, Stamenkovic V, Blizanac BB, Markovic NM, Ross PN, “Carbon-supported Pt-Sn electrocatalysts for the anodic oxidation of H2, CO, and H2/CO mixtures. Part II: The structure-activity relationship” J. Catal. 232 (2): 402-410 JUN 10 2005

Mun BS, Lee C, Stamenkovic V, Markovic NM, Ross PN, “A photoemission study of Pd ultrathin films on Pt(111)” J. Chem. Phys. 122(18): 184712 MAY 8 2005

13

Radmilovic V, Richardson TJ, Chen SJ, Markovic NM, Ross PN, “Carbon-supported Pt-Sn electrocatalysts for the anodic oxidation of H2, CO, and H2/CO mixtures. Part I. Microstructural characterization” J. Catal. 232 (1): 199-209 MAY 15 2005

Arenz M, Mayrhofer KJ, Stamenkovic V, Markovic NM, Ross PN, “The effect of the particle size on the kinetics of CO electrooxidation on high surface area Pt catalysts” J. Amer. Chem. Soc.127 (18): 6819-6829 MAY 11 2005

Mun BS, Lee C, Stamenkovic V, Markovic NM, Ross PN, “Electronic structure of Pd thin films on Re(0001) studied by high-resolution core-level and valence-band photoemission” Phys. Rev B 71 (11): 115420 MAR 2005

14

Future Plans

FY2007P.I. Retires from Berkeley Lab and program in its present form concludes

Good night and good luck !