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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 !