n m. markovic - energy.govon pt (covalent interactions) interplay of covalent, electrostatic and...
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N M. Markovic
H. Gasteiger and N. M. Markovic
H2 /CO
Cattech 4 (2000) 110
Fuel Cells and Electrocatalysis
HOR/HER : the mother of all electrochemical reactions
CO: a key “test molecule”
ORR/OER: a key for the development of alternative energies
More than just devise for energy conversion - the development of fuel cell catalysts in the last three decades has transformed electrocatalysis from art to science
MATERIALS-BY-DESIGN (111)
(100)
DESIGN
UHV FTIR SXS
STM/AFM RAMAN HRTEM
–– CHARACTERIZE
CHARACTIZATION METHODS
PHYSICAL CHEMICAL
–– SYNTHESIZE
SYNTHESIS METHODS
METALS
M -OXIDES
OXIDES
Reactants: O2, CH3OH, H2
M+ M+ M+M+
Pt(111)
OH = 0.70.85V
a)
DOUBLE-LAYER-BY-DESIGN
ANIONS
CATIONS
WATER
–– APPLY
Pt/C H2
O2
Fuel Cell Electrolyzer
REAL SYSTEM
Metal-Air Batteries
–– UNDERSTAND
Theory/Modeling Experiment
ACTIVITY, SELECTIVITY AND STABILITY MAPPING CsOH
LiOH KOH
Ru
Pt
Au
3
Single Crystals
Real Nano
Model Nano
Surface Science Approach
ORR- The reaction pathway
(H2O2)ad H2O
(H2O2)solution
(O2)ad O2
4e-
2e- 2e-
2H+ 2H+
Pt[111]-Skin
Pt[111]
H
up
d [%
]
60
30
0
60
30
0
O
xd
[%
]
E [V] vs. RHE
0.0 0.2 0.4 0.6 0.8 1.0
i [
A/c
m2]
60
30
0
-60
-30
E [V] vs. RHE
0.0 0.2 0.4 0.6 0.8 1.0
Rela
tive E
xp
an
sion
[%
]
-1.5
-1.0
-0.5
0.0
Pt3Ni(111)
Pt(111)
Atomic layer
1 2 3 4 5 6 7
Pt
[at.
%]
0
20
40
60
80
100
Ni
[at.
%]
100
80
60
20
0
40
a)
b)
c)
a’)
E [V] vs. RHE
0.0 0.2 0.4 0.6 0.8 1.0
i [m
A/c
m2]
-6
-4
-2
0
IIIIII
E [V] vs. RHE0.0 0.2 0.4 0.6 0.8 1.0
H
up
d
[%]
60
30
0
60
30
0
O
xd
[%
]
H2O
2 [
%]
Pt3Ni(111)
Pt(111)
Pt poly
0.1 HClO4
60oC
1600 rpm
0
50
i [
A/c
m2]
60
30
0
-60
-30
E [V] vs. RHE
0.0 0.2 0.4 0.6 0.8 1.0i
[mA
/cm
2]
-6
-4
-2
0
IIIIII
E [V] vs. RHE0.0 0.2 0.4 0.6 0.8 1.0
H
up
d
[%]
60
30
0
60
30
0
O
xd
[%
]
H2O
2 [
%]
Pt3Ni(111)
Pt(111)
Pt poly
0.1 HClO4
60oC
1600 rpm
0
50
i [
A/c
m2]
60
30
0
-60
-30
Potential/V
SXS
Metal Alloys(Pt3M)
[011
]
[01-1]
(110)-(1x1)
p(1x1)
Pt3Ni(110)
(e) Pt3Ni(100)
c(5x1)
(f)
Pt3Ni(111)(d)
[1-1
0]
[001]
E [V] vs. RHE
0.0 0.2 0.4 0.6 0.8 1.0 1.2
i [
A/c
m2]
-20
0
20
0.1M HClO4
(g)
Pt3Ni(111)
Pt(111)
CV
E [V] vs. RHE
0.0 0.2 0.4 0.6 0.8 1.0 1.2
i [
A/c
m2]
-20
0
20
(h)
Pt3Ni(100)
Pt(100)
E [V] vs. RHE
0.0 0.2 0.4 0.6 0.8 1.0 1.2
i [
A/c
m2]
-20
0
20
(i)
Pt3Ni(110)
Pt(110)
AES 3 keV
Auger Electron Energy [eV]
200 400 600 800
dN
(E)/
dE
(arb
. u
nit
s)
Pt 237
Pt390
Pt 158
Ni 848
Ni 783
Ni 716
Pt 251AES 3 keV
Auger Electron Energy [eV]
200 400 600 800
dN
(E)/
dE
(a
rb
. u
nit
s)
Pt 237
Pt390
Pt 158
Ni 848
Ni 783
Ni 716
Pt 251
Pt3Ni(hkl)
AES (a) LEED
E/E0
0.2 0.4 0.6 0.8
Inte
nsi
ty [
arb
. u
nit
s]
Pt 0.71
LEIS
Pt3Ni(hkl)
(b)
Surface composition = 100% Pt
Binding Energy [eV]-8 -6 -4 -2 0
Inte
nsi
ty [
arb
. u
nit
s]
UPS
(111)
(100)
(110)
(c)
Pt3Ni
Tailoring Electronic Properties
i = n F K(1-s) exp(-γGi / RT) Science, 315(2007)493
Nanosegregated Profile Activity mapping
Nature Materials, 6(2007)241
1st Layer
2nd Layer
3rd Layer
4th Layer
Pt=100 at.%
Pt=48 at.%
Ni=52 at.%
Pt=87 at.%
Ni=13 at.%
Pt=75 at.%
Ni=25 at.%
Pt[111]-Skin surface
Act
ivit
y fo
r O
RR
d-band center [eV]
2.63.03.4
Sp
ecif
ic A
cti
vit
y:
i k @
0.9
V [
mA
/cm
2
real]
0
1
2
3
4
5
Pt3Ti
Pt3V
Pt3Fe
Pt3Co
Pt3Ni
Pt-polyPt-skin surfaces
Pt-skeleton surfaces
Acti
vit
y i
mp
ro
vem
en
t fa
cto
r v
s. P
t-p
oly
1
2
3
d-band center [eV]
2.63.03.4
17
18
19
Target Activity Pt
3Ni(111)
Calculated d-band center [eV]
-3.0 -2.8 -2.6
Calc
ula
ted
acti
vit
y [
10
-2 e
V]
0
2
4
6
Pt
Pt3Ni
Pt3Co
Pt3Fe
Pt3Ti
(b)(a)
3.0 2.8 2.6
Calculated d-band center [eV]
Calc
ula
ted
acti
vit
y [
10
-2eV
]
0
2
4
6
Pt/C
d-band center shift (eV)
- - -
Maximize activity by minimizing surface coverage of spectators
Without compromising activity protect 3d elements by additional Pt layer
Tailoring Activity by Electronic Properties
Guiding Principles:
9
Colloidal solvo - thermal approach for monodispersed PtM NPs with controlled size and composition
1o Particle size effect applies to Pt-bimetallic NPs Specific Activity increases with particle size: 3 < 4.5 < 6 < 9nm
Mass Activity decreases with particle size Optimal size particle size ~5nm
Efficient surfactant removal
2o Temperature induced segregation in Pt-bimetallic NPs Agglomeration prevented
Optimized annealing temperature 400-500oC
(b)
3o Surface chemistry of homogeneous Pt-bimetallic NPs PtxM(1-x) NPs
Dissolution of non Pt surface atoms leads to Pt-skeleton formation
4o Composition effect in Pt-bimetallic NPs
Pt3M
Optimal composition of Pt-bimetallic NPs is PtM
1 nm
0.22 nm
1 nm1 nm
PtM PtM2 PtM3
Co KαPt Lα
Pt Co
Tailoring Electronic Properties
8
counts
Position (nm)
43 5210
Ni
Position (nm)
43 5210
Inte
nsit
y (
a.
u.)
Pt
counts
Position (nm)
43 5210
Calculated Profile
Intensity Counts
Inte
nsit
y (
a.
u.)
Position (nm)
43 5210
counts
Position (nm)43 5210
1 nm 1 nm
as-prepared acid leached acid leached/annealed
d
e
a
b
c
counts
Position (nm)
43 5210
Ni
Position (nm)
43 5210
Inte
nsit
y (
a.
u.)
Pt
counts
Position (nm)
43 5210
Calculated Profile
Intensity Counts
Inte
nsit
y (
a.
u.)
Position (nm)
43 5210
counts
Position (nm)43 5210
1 nm 1 nm
as-prepared acid leached acid leached/annealed
d
e
a
b
c
5o Pt-bimetallic catalysts with mutilayered Pt-skin surfaces
RDE after 4K cycles @60oC (0.6-1.05V vs. RHE):
8-fold specific and 10-fold mass activity improvements over Pt/C
0
100
200
300
400
Imp
ro
ve
men
t F
ac
to
r
(v
s.
Pt/C
)
Ma
ss
Ac
tiv
ity
(A
/g) before
after
0
2
4
6
0
10
20
30
40
50
60
Sp
ec
ific
Su
rfa
ce
Are
a (m
2/g
)
before
after
0.0
0.2
0.4
0.6
0.8
1.0
before
Sp
ec
ific
Ac
tiv
ity
(m
A/c
m2)
after
0
2
4
6
Imp
ro
ve
me
nt F
ac
to
r
(vs
. P
t/C
)
Pt/C acid leachedPtNi/C
acid leached/annealedPtNi/C
a
b
c
0
2
4
6
8
10
after before after 0
100
200
300
400
Imp
ro
ve
men
t F
ac
to
r
(v
s.
Pt/C
)
Ma
ss
Ac
tiv
ity
(A
/g) before
after
0
2
4
6
0
10
20
30
40
50
60
Sp
ec
ific
Su
rfa
ce
Are
a (m
2/g
)
before
after
0.0
0.2
0.4
0.6
0.8
1.0
before
Sp
ec
ific
Ac
tiv
ity
(m
A/c
m2)
after
0
2
4
6
Imp
ro
ve
me
nt F
ac
to
r
(vs
. P
t/C
)
Pt/C acid leachedPtNi/C
acid leached/annealedPtNi/C
a
b
c
before 0
4
8
10
14
From Model to Real Catalysts
6o Multimetallic NPs can further improve activity and durability
Au core PtFe shell Pt/C Au/PtFe
before before After 60K cycles After 60K cycles
Nano Letters, 11(2011)919-928
Advanced Functional Materials, 21(2011)147
Keep electronic properties constant
Maximize activity and selectivity by inert self assembled monolayer
Inert Pt-Calix[4]arene adlayer
Organic
Molecular patterning
Nature Materials, 9, 2010,881
Inorganic
Pt (111)
- O2
- SO4 / PO42- 3-
Pt (111)
- O2
- CN-
- SO4 / PO42- 3-
Pt (111)
- O2
- CN-
- M+
- M+(H2O)x-OHad
a)
b)
c)
Pt (111)
- O2
- SO4 / PO42- 3-
Pt (111)
- O2
- CN-
- SO4 / PO42- 3-
Pt (111)
- O2
- CN-
- M+
- M+(H2O)x-OHad
Pt (111)
- O2
- SO4 / PO42- 3-
Pt (111)
- O2
- SO4 / PO42- 3-- SO4 / PO42- 3-
Pt (111)
- O2
- CN-
- SO4 / PO42- 3-
Pt (111)
- O2
- CN-
- SO4 / PO42- 3-- SO4 / PO42- 3-
Pt (111)
- O2
- CN-
- M+
- M+(H2O)x-OHad
Pt (111)
- O2
- CN-
- M+
- M+(H2O)x-OHad
a)
b)
c)
Inert Pt-CNad adlayer
Nature Chemistry 2 (2010) 880
Beyond electronic effects
9
18
•ORR is strongly inhibited by adsorbed phosphoric acid anions
E [V vs. RHE]
0.0 0.2 0.4 0.6 0.8 1.0
Cu
rren
t d
ensi
ty [
A/c
m2
]
-6
-5
-4
-3
-2
-1
0
E [V vs. RHE]
0.0 0.2 0.4 0.6 0.8 1.0
Cu
rre
nt
de
ns
ity [
mA
/cm
2]
-6
-5
-4
-3
-2
-1
0
E [V vs. RHE]
0.0 0.2 0.4 0.6 0.8 1.0
Cu
rre
nt
de
ns
ity [
mA
/cm
2]
-100
-50
0
50
100
E [V vs. RHE]
0.0 0.2 0.4 0.6 0.8 1.0
Cu
rren
t d
ensi
ty [
A/c
m2]
-100
-50
0
50
100
a)
b)
c)
d)
Pt (111) – CN
0.05 M H2SO40.05 M H3PO4
Pt (111)
Pt (111) – CN
Pt (111)
E [V vs. RHE]
E [V vs. RHE]
Cu
rre
nt
de
nsit
y [
mA
/cm
2]
Cu
rre
nt
de
nsit
y [
mA
/cm
2]
III IIIIII III
III IIIIII III
E [V vs. RHE]
0.0 0.2 0.4 0.6 0.8 1.0
Cu
rren
t d
ensi
ty [
A/c
m2
]
-6
-5
-4
-3
-2
-1
0
E [V vs. RHE]
0.0 0.2 0.4 0.6 0.8 1.0
Cu
rre
nt
de
ns
ity [
mA
/cm
2]
-6
-5
-4
-3
-2
-1
0
E [V vs. RHE]
0.0 0.2 0.4 0.6 0.8 1.0
Cu
rre
nt
de
ns
ity [
mA
/cm
2]
-100
-50
0
50
100
E [V vs. RHE]
0.0 0.2 0.4 0.6 0.8 1.0
Cu
rren
t d
ensi
ty [
A/c
m2]
-100
-50
0
50
100
a)
b)
c)
d)
Pt (111) – CN
0.05 M H2SO40.05 M H3PO4
Pt (111)
Pt (111) – CN
Pt (111)
E [V vs. RHE]
E [V vs. RHE]
Cu
rre
nt
de
nsit
y [
mA
/cm
2]
Cu
rre
nt
de
nsit
y [
mA
/cm
2]
III IIIIII III
III IIIIII III
III IIIIII III
•CN adlayer selectively blocks adsorption of anions
Pt (111)
- O2
- SO4 / PO42- 3-
Pt (111)
- O2
- CN-
- SO4 / PO42- 3-
Pt (111)
- O2
- CN-
- M+
- M+(H2O)x-OHad
a)
b)
c)
Pt (111)
- O2
- SO4 / PO42- 3-
Pt (111)
- O2
- CN-
- SO4 / PO42- 3-
Pt (111)
- O2
- CN-
- M+
- M+(H2O)x-OHad
Pt (111)
- O2
- SO4 / PO42- 3-
Pt (111)
- O2
- SO4 / PO42- 3-- SO4 / PO42- 3-
Pt (111)
- O2
- CN-
- SO4 / PO42- 3-
Pt (111)
- O2
- CN-
- SO4 / PO42- 3-- SO4 / PO42- 3-
Pt (111)
- O2
- CN-
- M+
- M+(H2O)x-OHad
Pt (111)
- O2
- CN-
- M+
- M+(H2O)x-OHad
a)
b)
c)
Nature Chemistry 2 (2010) 880
i = n F K (1-s) exp(-γGi / RT)
E [V vs. RHE]
0.0 0.2 0.4 0.6 0.8 1.0
Cu
rren
t d
ensi
ty [
mA
/cm
2]
-6
-5
-4
-3
-2
-1
0
E [V vs. RHE]
0.0 0.2 0.4 0.6 0.8 1.0
Cu
rren
t d
ensi
ty [
A/c
m2
]
-6
-5
-4
-3
-2
-1
0
E [V vs. RHE]
0.0 0.2 0.4 0.6 0.8 1.0
Cu
rren
t d
ensi
ty [
A/c
m2
]
-100
-50
0
50
100
E [V vs. RHE]
0.0 0.2 0.4 0.6 0.8 1.0
Cu
rren
t d
ensi
ty [
A/c
m2]
-100
-50
0
50
100
0.1 M HClO40.1 M KOH
E [V vs. RHE]
Cu
rre
nt
de
nsit
y [
mA
/cm
2]
Cu
rre
nt
de
nsit
y [
mA
/cm
2]
E [V vs. RHE]
E [V vs. RHE] E [V vs. RHE]
Cu
rre
nt
de
nsit
y [
mA
/cm
2]
Cu
rre
nt
de
nsit
y [
mA
/cm
2]
a)
b)
c)
d)
Pt (111) – CN
Pt (111)
Pt (111) – CN
Pt (111)
III IIIIII III
III III III III
E [V vs. RHE]
0.0 0.2 0.4 0.6 0.8 1.0
Cu
rren
t d
ensi
ty [
mA
/cm
2]
-6
-5
-4
-3
-2
-1
0
E [V vs. RHE]
0.0 0.2 0.4 0.6 0.8 1.0
Cu
rren
t d
ensi
ty [
A/c
m2
]
-6
-5
-4
-3
-2
-1
0
E [V vs. RHE]
0.0 0.2 0.4 0.6 0.8 1.0
Cu
rren
t d
ensi
ty [
A/c
m2
]
-100
-50
0
50
100
E [V vs. RHE]
0.0 0.2 0.4 0.6 0.8 1.0
Cu
rren
t d
ensi
ty [
A/c
m2]
-100
-50
0
50
100
0.1 M HClO40.1 M KOH
E [V vs. RHE]
Cu
rre
nt
de
nsit
y [
mA
/cm
2]
Cu
rre
nt
de
nsit
y [
mA
/cm
2]
E [V vs. RHE]
E [V vs. RHE] E [V vs. RHE]
Cu
rre
nt
de
nsit
y [
mA
/cm
2]
Cu
rre
nt
de
nsit
y [
mA
/cm
2]
a)
b)
c)
d)
Pt (111) – CN
Pt (111)
Pt (111) – CN
Pt (111)
III IIIIII III
III III III III
Selectivity controlled activity
“Big vs. Small”
10
a) b)
c)
20 nm40 nm
a) b)
c)
20 nm40 nm
Improving stability of cathode catalysts
Nature Materials, 9, 2010,881
E [V vs. RHE]
0.0 0.2 0.4 0.6 0.8
Ch
arg
eden
sity
[
C/c
m2]
-5
0
5
10
15
20
25
30
E [V vs. RHE]
0.0 0.2 0.4 0.6 0.8
Cu
rren
t d
ensi
ty [
A/c
m2]
-100
-50
0
50
100
a)
b)
Pt (111)Pt (111)-APt (111)-BPt (111)-CPt (111)-D
III III
E [V vs. RHE]
0.0 0.2 0.4 0.6 0.8
Ch
arg
eden
sity
[
C/c
m2]
-5
0
5
10
15
20
25
30
E [V vs. RHE]
0.0 0.2 0.4 0.6 0.8
Cu
rren
t d
ensi
ty [
A/c
m2]
-100
-50
0
50
100
a)
b)
Pt (111)Pt (111)-APt (111)-BPt (111)-CPt (111)-D
III III
2% of active sites
Selectivity controlled stability
11
14
Maintain electronic properties and optimize stability by molecular patterning
Selective anode catalysts for the ORR and HOR are of grate importance for stability of cathode materials in Fuel Cells
17
Tailoring Activity/Stability by Molecular Patterning
Nano
Calix adlayer prevents adsorption of O2 but not H2
Extended
O2 H2
Pt(111)-Calix[4]arene
O2 + 4H+ +4e_ = H2O
H2 = 2H+ + 2e-
Reversible potential (E)
Act
ivit
y
Three Phase (Nafion) Interface
•What type of interactions are possible at three phase interfaces ?
18
Sulfonate anions are “specifically” adsorbed on Pt (covalent interactions)
Interplay of Covalent, Electrostatic and Non-covalent Interactions
Non-covalent cation-sulfonate interaction
Pt-beckbone interaction is very week (electrostatic forces)
26
J. Phys. Chem., C. (2010) .
19
27
The Spring Model
i = n F k (1-anions.) exp(-Gi/RT)
J. Phys. Chem., C. (2010) .
20
16
Perspectives
Understanding complexity (simplicity) of electrochemical interfaces all the way down to molecular and atomic levels will pave the way to:
16
Real
WATER
CYCLE
CARBON
CYCLE
LITHIUM
CYCLE
ENERGY
Energy
Conversion
Storage Group
&
Dramatic new energy production and storage technologies
Greatly improve our predictions for accelerating and directing chemical transformations
Enable new mitigation strategies for environmental damage
Chris Lucas
Jeff Greeley
Dusan Strmcnik,
Chao Wang Dennis van der Vliet
Dusan Tripkovic
Ram Subbaraman
Ken Kodama
Nemanja Danilovic
Masa Uchimura
Donguo Li
Pietro Lopez
Voya Stamenkovic
Gustav Wiberg
K-C Chang