New Electrocatalysts For Fuel Cells

Principal Investigator: Philip N. Ross, Jr.

Staff Scientist: Nenad M. Markovic

Post Doctoral Fellow: Thomas J. Schmidt

Vojislav Stamenkovic

Visiting Scientist: Ursula Paulus

Matthias Arenz

Berislav Blizanac

A research program conducted at the Lawrence Berkeley National Laboratory for the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Advanced Transportation Technologies of the U.S. Department of Energy under contract No. DE-AC03-76SF00098

Materials-by-Design Approach

synthesis of nanoparticles

Nafionfilm

Glassy-Carbon(RDE)

Catalysts

Characterization techniques

LEIS, XPS, AES, LEED HRTEM, XRD

Kinetics

HOR, ORR, CO Tolerance

HOR, ORR, CO Tolerance

Fuel cell catalyst

Taylor made surfaces

Modification oAl acac

CH3

Al CH3acac

Al

acac

CH3

Alacac

CH3

AlCH3

acac

AlCH3

acac

Collaborations

Industry

GM, Rochester, NY, USA Honda, Japan E-Tek, New Jersey, NJ, USA 3M, Minneapolis, MN, USA

Universities and Institutes

Max-Planck-Institut fuer Kohlenforschung, Muelheim/Ruhr, Germany

University of Ulm, Germany Paul-Scherrer-Insitut, Villigen, Switzerland Universidad d’Alicante, Spain Texas Tech University, Lubbock, TX, USA University of Eindhoven, Holland University of Wales, UK University of Bonn, Germany University of Liverpool, UK

Future Research 2000

Anode Side

Optimization of PdAu catalysts

Stoichiometry and particle size

Electrocatalysis on Pd thin metal films

Electronic effects

Select the most promising substrate for the Pd thin filmelectrode concept

Simulation of ‘Air-bleed’

on FC catalysts under FC conditions

Cathode Side

Optimization of PtNi and PtCo catalysts

Stoichiometry

Minimization of Pt amount

Pt-skin effects (electronic modification of Pt)

Anion effects

New class of ORR catalysts

Publications (Since 10/2000)

Refereed Journals and Refereed Conference Proceedings:

Markovic, N. M. and P. N. Ross, “Electrocatalysts by Design: From the TailoredSurface to a Commercial Catalyst”, Electrochim. Acta, 45, 4101, 2000.

Markovic, N. M. and P. N. Ross, “New Electrocatalysts for Fuel Cells: From ModelSurfaces to Commercial Catalysts”, CATTECH 4 (2000) 110.

V. Stamenkovic, N. M Markovic, P. N. Ross, “Structure-relationships inelectrocatalysis: Oxygen Reduction and Hydrogen Oxidation Reactions on Pt(111) and Pt(100) in Solution Containing Chloride Ions”, J. Electroanal. Chem. 500 (2001) 43.

T.J. Schmidt, B. N. Grgur, N.M. Markovic, and P.N. Ross, “Oscillatory Behavior inthe Electrochemical Oxidation of Formic Acid on Pt(100): Rotation and Temperature Effects”, J. Electroanal. Chem. 500 (2001) 43.

C. Saravanan, N.M. Markovic, M. Head-Gordon, P.N. Ross, “Stripping and BulkCOElectro-oxidation at the Pt-Electrode Interface: Dynamic Monte Carlo Simulations”, J. Chem. Phys. 114 (2001) 6404.

N. M Markovic, T.J. Schmidt, V. Stamenkovic, P.N. Ross, “Oxygen ReductionReaction on Pt and Pt Bimetallic Surfaces: A Selective Review”, Fuel Cells-FromFundamentals to Systems 1(2001)105-116.

T.J. Schmidt, V. Stamenkovic, C.A. Lucas, N.M. Markovic, and P.N. Ross, “SurfaceProcesses and Electrocatalysis of the Pt(hkl)/Bi –Solution Interface”, PhysicalChemistry Chemical Physics 3 (2001)3879.

T.J. Schmidt, N.M. Markovic, and P.N. Ross, “Temperature-Dependent SurfaceElectrochemistry of Pt Single Crystal Surfaces in Alkaline Solution Part I. COOxidation”, J.Phys. Chem, B 105 (2001)12082.

Koper, MTM; Schmidt, TJ; Markovic, NM; Ross, PN. “Potential Oscillations and S-shaped Polarization Curve in the Continuous Electro-oxidation of CO on Pt Single-crystal Electrodes”, J. Phys. Chem. B 105 (2001) 8381.

Future Directions

Unified concept for both anode and cathode catalysts utilizing PGM-based bimetallic nanoparticles with “grape” structure (PGM skin with base metal core)stability of high surface area Pt-bimetallic catalysts

Choice of skin and core metals different for anode and cathode

New synthetic chemistry for nanoparticles with “grape” structure

Investigation of Re as metal core in PGM “grape”structured nanoparticles

Pt and Pd monolayers on Re(0001) model system

Re colloidal chemistry

Optimization of AuPd anode catalyst for HT membranes

Computational screening of non-PGM catalyst concepts using newly developed (under BES funding)ab initio theory of the ORR

Segregation on Pt3Ni and Pt3Co alloys surfaces

ResultsGroupGrenoble

Y.Gauthier, Surface Review and Letters, 3(1996)1663

AES

Pt3Co annealed

Pt3Co sputtered

Auger electron energy [eV]200 400 600 800

dN(E

)/dE

[arb

.uni

ts]

Pt3Co annealed

E/E0

0.4 0.6 0.8co

unts

[kH

z]

LEIS Ne+

a)

b)

E/E0

0.4 0.6 0.8

coun

ts [k

Hz]

LEIS Ne+

Pt3Co sputtered

c)

Pt251Pt237Pt158

Pt390 Co656

Co716

Co775 Co

Pt

Pt

Co

PtPlatinum ‘Skin’ on the surface

Pt3Co: AES, LEIS

AES:

-Co depeleted on the annealed surfaces

-Pt enrichment?

LEIS:

-Complete Pt enrichment on the annealed surface

-Bulk composition achievedduring in situ sputtering

Skin structure is either more or less active than sputtered structure

factor:

% H

2O2 ; i

R/µ

A

0

10

20

E/V vs RHE0.0 0.2 0.4 0.6 0.8 1.0

i D/m

Acm

-2

-4

-2

0

Pt3Co skinPt-poly

1600rpm

Pt3Ni skin

0.1M HClO4

333K

i k[m

A/c

m2 ]

2

4

6

8

10

12

14 0.1M HClO4 @ 0.85V 333K

Pt Pt3Ni Pt3Co

Sputtered SurfaceAnnealed surfaceSputtered SurfaceSkin Structure

Kinetic Enhancement by Skin Effect

The most active surface at 60°C: Pt3Co skin

Pt3Co (s) > Pt3Co (b) > Pt3Ni (b) >Pt > Pt3Ni (s)4.2 2.8 1.9 1 0.15

Electronic effects

Characterization of Pt/Vulcan Catalyst

10 nm

Particle Size [nm]

0 1 2 3 4 5 6 7 8 9 10

Freq

uenc

y [%

]

0

5

10

15

20

25

30

d~3.5 nm

low magnification

Transmision electron microscopy

5 nm

(111)

(100)

Mainly cubo-octahedral particleswith (111) and (100) facets

high magnification

The particle size effects:Correlation between the ORR on Pt(hkl) andexposed facets on Pt/C catalysts at fuel cells relevant conditions

3 nm3 nm

6 nm6 nm

mean particle size [nm]2.53.03.54.04.55.0

i [m

Acm

-2re

al ]

d=3.1 ± 1 nm, 3.3 ± 0.7 nm, 3.8 ± 1.7 nm, 4.7 ± 2.7 nm

catalysts: 10, 20, 30, 40% Pt/C

KOH

H2SO4

SA increases with SAD(100, e+c)

Particle size effect

10 % Pt/Vulcan

40 % Pt/Vulcan

SA increases with SAD(111)

E [V/RHE]

0.0 0.2 0.4 0.6 0.8 1.0

I [m

A/c

m2 ]

-1.0

-0.8

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

20% Pt/Vulcan20% PtNi/VulcanPt3Ni/Vulcan

Hupd coverage decreases with increase of Ni or Co wt%

(a)

Complete alloying

0.1M HClO4333K

HR Transmision electron microscopy

Pt/VulcanPtNi/VulcanPt3Ni/Vulcan

Characterization of PtCo/Ni Vulcan Catalysts

Cubo-octahedral shapewith (111) and (100) facets

PtM

ORR Kinetics on Pt-bimetallic SurfacesFuel Cells Relevant Conditions

Some Pt-M alloys have better performance than Pt

Pt-Co has the highest activity

i k [m

A/m

g Pt]

0

50

100

150

200

250

300

350

@ 850 mV @ 900 mV

0.1 M HClO4, 333 K, Anodic Step (hold 10 min./potential)

40 % Pt 50 % Pt PtCr PtFe PtCo PtNi

Benefits:Higher activity (!?) Substitution of Pt

n ~ 2

n < 1e)

n > 2

n = 10.6 0.8 1.0

Inte

nsity

/ a.

u.

n < 1

Pd

Pt

E1/E0

0.6 0.8 1.0

Inte

nsity

/ a.

u.n = 1

PtPd

Pt(111)

b)

E/V [RHE]0.0 0.2 0.4 0.6

0.05M H2SO4 293K

Pt(111) - nML Pd

x5Pt(111) n = 1

n ~ 2

n > 2

n < 1

E1/E0

E1/E0

0.6 0.8 1.0

Inte

nsity

/ a.

u. Pd

n > 1

c)

a)

d) 0.15 mA/cm2

0.25 mA/cm2

Pd thin metal films on Pt(111)

Pt(111)-Pd

E [V/RHE]0.0 0.2 0.4 0.6

j [m

Acm

-2]

-3

-2

-1

0

1

2

Pt(111)-1ML PdPt(111)-0.65ML PdPt(111)-0.42ML Pd

Pt(111)

Pt(111)-1ML PdPt(111)-0.65ML Pd

Pt(111)-0.42ML Pd 0.05M H2SO4

E [V/RHE]-0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2

i [m

Acm

-2]

-1

0

1

2

3

Pt (111)-1ML PdPt (111)-0.65ML PdPt (111)

HOR 0.1 M KOH 1600 rpm 293 K

ΘPd / MS

0.0 0.5 1.0 1.5 2.0 2.5 3.0

i k / m

Acm

-2

0.4

0.6

0.8

1.0

1.2

1.4 Pt(111)-Pd0,05M H2SO4

HER/HOR on Pt(111)-Pd in H2SO4/KOH

Maximum catalytic activity for 1 MLof Pd film

Adsorption vs Absorption of H

Activation energy:

Reduced by 50% on 1ML Pd

E [V/RHE]0.0 0.2 0.4 0.6 0.8 1.0

i [m

Acm

-2]

-5

-4

-3

-2

-1

0

Pt(111)Pt(111)-1ML PdPt(111)-1.5 ML Pd

I [µA

]

0

20

400.1 M KOH50 mV/s, 1600 rpm, 293 K

Electronic Effect

amount Pd / ML0.0 0.5 1.0 1.5 2.0

-I /m

Acm

-2

0

1

2

3

4 @ 0.9V

2

ORR on Pt(111)-x Pd in KOH

“Vulcano Plot”

ORR on UHV Prepared Au(hkl)-Pd Alloy Surfaces

i k[m

A/c

m2 ]

0

2

4

6

8

10 0.1M KOH @ 0.85V

333K

Au(111)

+30

%Pd

+50

%Pd

Au(100)

+30

%Pd

+50

%Pd

+0 %

Pd

+0 %

Pd

ORR

Pd coverage [%]0 20 40 60 80

i k [m

A/c

m2 ]

0

2

4

6

8

10

Au(111) + Pd

Au(100) + Pd

Structural Effect

Electronic Effect

Vapor deposition of Pd

50 % Pd

Inte

nsity

(arb

. uni

ts)

30 % Pd

Au(hkl)-PdLEIS He+

75 % Pd

E/E0

0.6 0.8 1.0

Pd

Pd

Pd

Au

Au

Au