Fuel Cells and a Nanoscale Approach to Fuel Cells and a Nanoscale Approach to Materials DesignMaterials Design
Chris LucasChris Lucas
Department of PhysicsDepartment of Physics
Outline
PEM fuel cells (issues)
A nanoscale approach to materials design
What is a fuel cell? A fuel cell is an electrochemical energy conversion device
It converts hydrogen and oxygen into water and produces electricity
The chemicals (fuel) flow continuously unlike in a battery
Several types:(1)PEM (transportation applications)(2)Solid oxide fuel cell (stationary applications, co-generation of heat and power)
Hydrogen Cars: Fad or the Future? Science, June 2009
Hydrogen Cars: Fad or the Future? Science, June 2009
Proton Exchange Membraneor
Polymer Electrolyte Membrane
PEM Fuel Cell Technology
Membrane is a permeable polymer sheet which allows protons (H atoms) to pass through Operate at low temperatures with high power density Low cost, small size, high performance Ideal for transportation, stationary and portable applications
Energy Storage and Conversion: Fuel Cells
Efficiency issues:
Membrane transport
Anode:Impurity-tolerant catalyst
Cathode:A good catalyst for oxygen reduction reaction (ORR)(1/2O2+2H++2e- = H2O)
Nanoscale and Surface Physics: Catalyst Materials by Design
Catalyst Issues
(1) Substantial overpotential for the ORR reduces the thermal efficiency to 43% at 0.7 V [compared to 87% at reversible ORR potential (1.23 V)]
(2) Pt is expensive (Pt-loading)
(3) Performance degrades too quickly due to dissolution (stability issue)
Question: Can we use modern experimental methods to design a nanoscale catalyst?
Tailoring surface properties at the atomic level
Bifunctional effects:
Effects can be: (1) Ensemble (2) Electronic
Nanoscale and Surface Physics: Catalyst Materials by Design
M to do something else?
Pt for catalysis
Bimetallic Pt-alloy surfaces - Pt3M
Modern Experimental Methods
UHV preparation and characterization
Transfer to liquid environment for activity measurements
Transfer back to observe changes-or even better, have a look in-situ
(1) Polycrystalline materials(2) Single crystals
Calculated d-band center [eV]
-3.0 -2.8 -2.6
Cal
cula
ted
acti
vity
[10
-2 e
V]
0
2
4
6
d-band center [eV]
2.63.03.4Spec
ific
Act
ivit
y: i k
@ 0
.9V
[m
A/c
m2 re
al]
0
1
2
3
4
Pt3Ti
Pt3V
Pt3Fe
Pt3CoPt3Ni
Pt-polyPt-skin surfaces
Pt-skeleton surfaces
Act
ivit
y im
prov
emen
t fa
ctor
vs.
Pt-
poly
1
2
3
d-band center [eV]
2.63.03.4Spec
ific
Act
ivit
y: i k
@ 0
.9V
[m
A/c
m2 re
al]
0
1
2
3
4
Pt3Ti
Pt3V
Pt3Fe
Pt3CoPt3Ni
Pt-polyPt-skin surfaces
Pt-skeleton surfaces
Act
ivit
y im
prov
emen
t fa
ctor
vs.
Pt-
poly
1
2
3
Calculated d-band center [eV]
-3.0 -2.8 -2.6
Cal
cula
ted
acti
vity
[10
-2 e
V]
0
2
4
6
d-band center [eV]
2.63.03.4Spec
ific
Act
ivit
y: i k
@ 0
.9V
[m
A/c
m2 re
al]
0
1
2
3
4
Pt3Ti
Pt3V
Pt3Fe
Pt3CoPt3Ni
Pt-polyPt-skin surfaces
Pt-skeleton surfaces
Act
ivit
y im
prov
emen
t fa
ctor
vs.
Pt-
poly
1
2
3
ad) term
Gad termand
ad) term
Pt
Pt3Ni
Pt3Co
Pt3Fe
Pt3Ti
(a) (b)
Trends in catalytic activity across the Periodic Table (3d metals)
Strong link between atomic/electronic structure and activity both from theory and experiment(d-band center is proportional to adsorption strength)
Nature Materials, v6, p241 (2007)
Model Electrocatalysts: Pt3Ni crystals
electrolyte out
electrolyte in
counter electrode
crystal
working electrode
polypropylene film
reference electrode (SCE)
electrolyte out
electrolyte in
counter electrode
crystal
working electrode
polypropylene film
reference electrode (SCE)
Model Electrocatalysts: Pt3Ni crystals
XMaSthethe UK-CRGUK-CRG
( 1 1 1 ) f a c e t s
P t 3 N i - n a n o p a r t i c l e s
0 . 1 H C l O 4
6 0 o C@ 0 . 9 V v s . R H E
d - b a n d c e n t e r p o s i t i o n v s F . L . [ e V ]
2 . 42 . 52 . 62 . 72 . 82 . 93 . 03 . 13 . 2
Sp
ecif
ic A
ctiv
ity
i k [ m
A/c
m2 ]
0
5
1 0
1 5
P t ( 1 1 0 )P t ( 1 1 1 )
P t ( 1 0 0 )
P t 3 N i ( 1 1 1 )
P t - p o l y
P t 3 N i - p o l y
1 0
0
5
Act
ivit
y Im
pro
vem
ent
Fac
tor
vs. P
t-p
oly
P t 3 N i ( 1 0 0 )
P t 3 N i ( 1 1 0 )
E x t e r i o r S n a p s h o t [ 0 0 1 ] C r o s s S e c t i o n( b )
( a )
[ 0 1 1 ]
[ 0 1 - 1 ]
B i n d i n g E n e r g y [ e V ]
02468
Inte
nsi
ty [
arb
. un
its]
B i n d i n g E n e r g y [ e V ]
02468
Inte
nsi
ty [
arb
. un
its]
x - S p u t t v s y - S p u t t
E / E 0
0 . 2 0 . 4 0 . 6 0 . 8
Inte
nsi
ty [
arb
. un
its]
P t 0 . 7 1
[ 0 1 1 ]
[ 0 1 - 1 ]
B i n d i n g E n e r g y [ e V ]
02468
Inte
nsi
ty [
arb
. un
its]
B i n d i n g E n e r g y [ e V ]
02468
Inte
nsi
ty [
arb
. un
its]
x - S p u t t v s y - S p u t t
E / E 0
0 . 2 0 . 4 0 . 6 0 . 8
Inte
nsi
ty [
arb
. un
its]
P t 0 . 7 1
Key results from combined studies:
[ 0 1 1 ]
[ 0 1 - 1 ]
B i n d i n g E n e r g y [ e V ]
02468
Inte
nsi
ty [
arb
. un
its]
B i n d i n g E n e r g y [ e V ]
02468
Inte
nsi
ty [
arb
. un
its]
x - S p u t t v s y - S p u t t
E / E 0
0 . 2 0 . 4 0 . 6 0 . 8
Inte
nsi
ty [
arb
. un
its]
P t 0 . 7 1
[ 0 1 1 ]
[ 0 1 - 1 ]
B i n d i n g E n e r g y [ e V ]
02468
Inte
nsi
ty [
arb
. un
its]
B i n d i n g E n e r g y [ e V ]
02468
Inte
nsi
ty [
arb
. un
its]
x - S p u t t v s y - S p u t t
E / E 0
0 . 2 0 . 4 0 . 6 0 . 8
Inte
nsi
ty [
arb
. un
its]
P t 0 . 7 1
(1)Surfaces are 100% Pt
(2) Segregated surfaces are stable during reactions
(3) Activity depends on atomic geometry
Science, v315, p493 (2007)
Nanoscale and Surface Physics: Catalyst Materials by Design
Real catalysts are nanoparticle arrays
TEM shows nanoparticles governed by ECS
[ 0 1 1 ]
[ 0 1 - 1 ]
B i n d i n g E n e r g y [ e V ]
02468
Inte
nsi
ty [
arb
. un
its]
B i n d i n g E n e r g y [ e V ]
02468
Inte
nsi
ty [
arb
. un
its]
x - S p u t t v s y - S p u t t
E / E 0
0 . 2 0 . 4 0 . 6 0 . 8
Inte
nsi
ty [
arb
. un
its]
P t 0 . 7 1
DFT and Monte-Carlo calculations for nanoparticles
These nanoparticles have yet to be engineered
Pt75Ni25 -[111]- Nanoparticles
Atomic Layer
Con
cen
trat
ion
of
Pt
Ato
ms
0
20
40
60
80
100
1 2 3Atomic Layer
[001] Cross Section
Monte Carlo iterations [x103]
0 20 40 60 80 100
Ave
rgae
Ato
mic
En
ergy
[eV
]-5.18
-5.16
-5.14
-5.12
-5.10
-5.08
-5.06(a) (b)- Pt - Ni
Bulk Ratio
Tetrahedron
Octahedron
Science, v324 (April, 2009)
Just a Dream-or Future Reality?
Nitrogen coordinated Fe in a carbon matrix now matches Pt/C
Turnover frequency= number of electrons per active site per second
Summary
• Fuel cells offer significant potential climate and energy security benefits
• Materials design from fundamental nanoscale studies
• This approach could be used in a range of materials (and energy) applications
Note: The University of Birmingham is the only UK institution to work on all aspects of Hydrogen energy research
