-
WP7: Polymer Electrolyte Fuel cells
Anthony R. J. Kucernak
Department of Chemistry
Imperial College London
London UK SW7 2AZ
[email protected]
H2FC Supergen, Newcastle, 30-31 July
-
Rational design of fuel cell components
Plus: Reduced platinum loading
CORE: Corrosion of
catalyst support
CORE: Efficient
utilisation of reactants
Performance Longevity
Cost
-
CORE [Performance] – Imaging of reactant transport
Challenges
• What level of fidelity is required in models
• How to efficiently distribute reactants throughout a fuel
cell
Approaches
• Ex-situ imaging of reactant transport in fuel cells
Ambition
• Rational design of flow fields and materials
• Validation of computational approaches
Plus: Reduced platinum loading
CORE: Corrosion of
catalyst support
CORE: Efficient
utilisation of reactants
Performance Longevity
Cost
-
CORE – “A NEW REACTIVE GAS FLUX
IMAGING METHOD BASED ON
CHEMILUMINESCENCE”
T. Lopes, B Kakati, M Ho, A Kucernak, J. Power Sources,
submitted
-
Different geometries of flow fields
Fuel Cells and Hydrogen - 2013-2014
Many flow field designs are propriety
• Square contact
• Parallel
• interdigitated
• Serpentine
• Meander
-
Different types of material for reactant
transport layers
-
How are reactants distributed within the PEFC?
Measure reactant
concentration in catalyst
layer under a range of
operating conditions
Single PEFC Test Unit
To scale
-
Modelling studies of reactant distribution in
channels/transport media
Park, J.; Li, X., An experimental and numerical investigation on
the cross flow through gas diffusion layer in a PEM fuel cell with
a serpentine flow channel. Journal of Power Sources 2007, 163 (2),
853-863
Phong Thanh Nguyen, Torsten Berning, Ned Djilali , Computational
model of a PEM fuel cell with serpentine gas flow channels, Journal
of Power Sources 130 (2004) 149–157
-
Can We Image the Gas partial presure at the Catalyst Layer
Interface?
-
How To Image the Flux of “Oxygen” at the Catalyst Layer
Interface
(a) Reid, R. C.; Sherwood, T. K., The Properties of gases and
liquids : their estimation and correlation. McGraw-Hill: New York ;
London, 1958; (b) Ono, R.; Oda, T., Spatial distribution of ozone
density in pulsed corona discharges observed by two-dimensional
laser absorption method. Journal of Physics D-Applied Physics 2004,
37 (5), 730-735. (c) Ermel, M.; Oswald, R.; Mayer, J. C.; Moravek,
A.; Song, G.; Beck, M.; Meixner, F. X.; Trebs, I., Preparation
Methods to Optimize the Performance of Sensor Discs for Fast
Chemiluminescence Ozone Analyzers. Environmental Science &
Technology 2013, 47 (4), 1930-1936
Ozone as a Proxy gas to
Bi molecular Oxygen
(Similar Binary Diffusion
Coefficients in N2, 0.175
cm2 s-1 and 0.16 cm2 s-1)a,b
Taking Advantage of the
Instantaneous Chemiluminescent
Reaction of O3 with a Dye –
HIGHER SPATIAL and TEMPORAL
Resolutionsc
Temporal and spatial resolution:
0.040 sec and 0.055 mm
-
Experimental Set-Up – Ex-situ “fuel cell”
Optical O3 Sensor
€200
Flow field 27x27 mm
0.8mm channels, 1.6mm land
-
Effect of flow rate on reactant transport
27 mm
27 m
m
-
Effect of flow rate on reactant transport
-
Effect of flow rate on reactant transport
-
Effect of flow rate on reactant transport
-
Effect of flow rate on reactant transport
-
Effect of flow rate on reactant transport
-
Light intensity varies with reactant flow rate
Re = 245
Re = 551
Augmenting The Flux
(mL min-1)
-
Transport in the “GDL” – not just diffusion
Channel
Modelling
200ccm 450ccm
Gas Inlet Gas Inlet
Gas Outlet
Beale, S. B., Conjugate mass transfer in gas channels and
diffusion layers of fuel cells. Journal of Fuel Cell Science and
Technology 2007, 4 (1), 1-10.
“Gas diffusion” Layer
NOT gas diffusion layers – “Reactant transport layers”
-
Asymmetry at higher flow rates
200ccm 450ccm
Gas Inlet Gas Inlet
Gas Outlet
-
Convective Flow In the Gas Transport Media
Arrows Are
Ilustrative
Only
-
Convective Flow In the Gas Transport Media
Bar 0 1x10
-52x10
-53x10
-50.0
5.0x105
1.0x106
1.5x106
2.0x106
2.5x106
3.0x106
3.5x106
Inte
gra
ted
lig
ht
inte
ns
ity
/ a
.u.
PO
3
Consumed / Pa
Fixed 150 sccm of air
Variation in PO3
/Bar
Light -d[O3]/dt=k[O3] c.f. J = A k0 [O2] aH
+ exp(αηRT/F)
-
Sensitivity to properties of Reactant Transport layer
Microporous Layer
Carbon Paper
Hydrophobic Agent (PTFETM)
-
0.0 1.0x10-5
2.0x10-5
3.0x10-5
0.0
5.0x105
1.0x106
1.5x106
2.0x106
2.5x106
3.0x106
3.5x106
PO
3
Consumed / Pa
To
tal
Pix
el
Inte
ns
ity
/ a
.u.
"G
en
era
ted
up
on
Re
ac
tio
n"
The Constituents of a Gas Transport Medium and the Partial
Pressure of the Reactive Gas at the Catalyst Layer Interface
350 mL min-1 Air
Re = 429 /Bar
/Bar /Bar
Toray (TGP-H-60)
-
CORE [Performance] – Corrosion of catalyst support
Challenges
• Transient events lead to local voltage spikes
• These lead to degradation of systems
• Testing takes a long time (hundreds of start/stop cycles)
Approaches
• Development of in situ reference electrode
Ambition
• Measure effect and dependence on important parameters
• Devise and test mitigation strategies
Plus: Reduced platinum loading
CORE: Corrosion of
catalyst support
CORE: Efficient
utilisation of reactants
Performance Longevity
Cost
-
CORE – IN SITU REFERENCE ELECTRODES
FOR MEASURING LOCAL POTENTIALS
Graham Smith, Christopher M. Zalitis, Anthony R.J. Kucernak,
Electrochemistry Communications, 43(2014), 43-46
-
Transient effects during startup of fuel cells
• Formation of corrosion cell at moving
boundary
• Transient high potentials
Anode flow field Cathode flow field
1
2inlet
outlet inlet
outlet
1
2
-2 -1 0 1 2 3 4 5 6-1000
-800
-600
-400
-200
0
200
400
600
800
Anode (position 1)
Cathode (position 1)
Anode (position 2)
Cathode (position 2)
Po
tential vs IO
RE
/ m
V
Time / s
-200
0
200
400
600
800
1000
1200
1400
Po
ten
tia
l vs R
HE
/ m
V
a
b
O2/N2
-
Anode flow field Cathode flow field
1
2inlet
outlet inlet
outlet
1
2
-2 -1 0 1 2 3 4 5 6-1000
-800
-600
-400
-200
0
200
400
600
800
Anode (position 1)
Cathode (position 1)
Anode (position 2)
Cathode (position 2)
Po
tential vs IO
RE
/ m
V
Time / s
-200
0
200
400
600
800
1000
1200
1400
Po
ten
tia
l vs R
HE
/ m
V
a
b
C.A. Reiser, L. Bregoli, T.W. Patterson, J.S. Yi, J.D. Yang,
M.L. Perry, T.D. Jarvi, Electrochem. Solid State Lett., 8, A273
(2005).
Transient effects during startup of fuel cells
-
How to measure local electrochemical potential
In plane
G. Hinds and E. Brightman, Electrochem. Commun. 17 (2012)
p.26–29
-
Solid state reference electrode
Solid polymer electrolyte
Reference electrode attached to 10 m
thick porous polycarbonate conductor
3 mm 30 mm8 μm
-
Stable reference potential
• Stable potential with time
• Measure local pH
• Important for Alkaline PEFC
0 5 10 15 20 25820
840
860
880
900
920
0 2 4 6 8 10 12
0
200
400
600
800
Po
ten
tia
l / m
V v
s R
HE
Time / hr
pH
Po
ten
tial / m
V v
s. S
CE
0.0 0.5 1.0 1.5 2.0 2.5 3.0
0
20
40
60
80
100
Charge
Discharge
Time / hr
Ch
arg
e P
ote
ntial / m
V v
s R
HE
0
100
200
300
Dis
ch
arg
e P
ote
ntial / m
V v
s R
HE
a
b
CO2 HCO3
-
-
Transient potential variation during startup
• Transient production of 1.4 V
• Corrosion correlated to position in
cell
• Mitigation strategies being
examined
Anode flow field Cathode flow field
1
2inlet
outlet inlet
outlet
1
2
-2 -1 0 1 2 3 4 5 6-1000
-800
-600
-400
-200
0
200
400
600
800
Anode (position 1)
Cathode (position 1)
Anode (position 2)
Cathode (position 2)
Po
tential vs IO
RE
/ m
V
Time / s
-200
0
200
400
600
800
1000
1200
1400
Po
ten
tia
l vs R
HE
/ m
V
a
b
Graham Smith, Christopher M. Zalitis, Anthony R.J. Kucernak,
Electrochemistry Communications, 43(2014), 43-46
-
Plus [Cost] – Reduce catalyst loading
Challenges
• What would the ideal electrode structure be?
• What is the ultimate performance
Approaches
• Develop a fuel cell with new electrode structure
Ambition
• Characterise limits of performance
• Bottom up approach for electrode design
Plus: Reduced
loaplatinum ding
CORE: Corrosion supportof catalyst
CORE: Efficient
utilisation of reactants
Performance Longevity
Cost
-
FLEXIBLE : BUILDING THE “PERFECT”
PEFC FUEL CELL ELECTRODE
-
35
Efc
(V) 1889
1960 1989 2003
2006
L. Mond and C. Langer, Proc. R. Soc. London 46, 296 (1889). W.
Grubb and L. Niedrach, J. Electrochem. Soc. 107, 131 (1960). I.D.
Raistrick, US Patent No. 4876115, 1989. W.L. Gore and Associates,
GORE® PRIMEA® MEAs for Transportation (2003). M.K. Debe et al., J.
Power Sources 161, 1002 (2006).
Advances in performance of polymer electrolyte fuel cells
specific activity
Platinum all over again…
From Michael Eikerling
SFU, Canada
-
200
m
What would an ideal structure look like?
Substrate: thin (< 10 μm),
high electrical conductivity
Condensed phase
Pore: Fast diffusion of reactants
with no condensation
Pt/C agglomerate: 0.5 μm
Gas phase
Fast access of protons
36
-
Use any catalyst
•E.g. 0.16 µg cm-2 Pt (60wt% JM HiSPEC 9100)
10 µm thick GDL
400 nm diameter hydrophobic pores
Tortuosity = 1
SEM images of such an
electrode
13 µm
37
-
Catalyst Loadings
0.16 µgPt cm-2 0.5 µgPt cm
-2
1 µgPt cm-2 2.5 µgPt cm
-2
Uniform homogeneous layer across the macro and micro scale
C. M. Zalitis, D. Kramer and A. R. Kucernak, Phys. Chem. Chem.
Phys., 15, 4329, (2013).
2 mm
60% Pt/C catalyst, Alfa
Aesar, HiSPEC 9100
38
-
ORR: Gaseous diffusion test
0.2 0.4 0.6 0.8 1.0 1.2
-180
-160
-140
-120
-100
-80
-60
-40
-20
0
20
-779
-692
-606
-519
-433
-346
-260
-173
-87
0
87
j Ge
om
etr
ic /
mA
cm
-2
j Sp
eci
fic /
mA
cm
-2
E / V vs. RHE
Floating electrode
RDE limitation (10k rpm)
P[O2]/P[total] = 0.21
Carrier gas:
Nitrogen
Helium
0.70 0.75 0.80 0.85 0.90 0.95 1.00
-6
-5
-4
-3
-2
-1
0j S
peci
fic /
mA
cm
-2
E / V vs. RHE
105 A cm-2
282 A cm-2
-160
-142
-125
-107
-89
-71
-53
-36
-18
0
18
j Ma
ss /
A m
g-1
Catalyst: 60% Pt/C catalyst, Alfa Aesar, HiSPEC 9100, 4.0 mol
dm-3 HClO4,O2,
298 K, 10 mV s-1,4.9 µgPt cm-2
220 O2 molecules/Pt/s -2.0 -1.8 -1.6 -1.4 -1.2 -1.0 -0.8
-2.5
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
Gradient = 1.29
Gradient = 1.04
Gradient = 1.02
J at 0.9 V Vs. RHE
J at 0.7 V vs. RHE
J at 0.4 V vs. RHE
log
(JS
pecific /
mA
cm
-2)
log(P(O2) / atm)
0.2 0.4 0.6 0.8 1.0 1.2
-14
-12
-10
-8
-6
-4
-2
0
2
p(O2) = 0.013 - 0.001
JS
pecific /
mA
cm
-2
E / V vs. RHE (IR corrected)
-
-0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2-9
-8
-7
-6
-5
-4
-3
-2
-1
0
1
-8010
-7120
-6230
-5340
-4450
-3560
-2670
-1780
-890
0
890
jM
ass /
A m
g-1
j Sp
ecific /
A c
m-2
E / V vs. RHE
0.0 0.2 0.4 0.6 0.8 1.0 1.20.0
0.1
0.2
0.3
0.4
0.5
0.6
Floating Electrode
RDE limitation (10k rpm)
j Sp
ecific / A
cm
-2
E / V vs. RHE
-7.6
-6.8
-5.9
-5.1
-4.2
-3.4
-2.5
-1.7
-0.8
0.0
0.8
j Ge
om
etr
ic /
A c
m-2
HOR/HER on Low Pt Loading Electrodes
0.55 A cm-2
1300 H2 molecules s-1/Pt site
Catalyst: 60% Pt/C catalyst, Alfa Aesar, HiSPEC 9100, 4.0 mol
dm-3 HClO4,O2, 298 K, 10 mV s
-1,2.2 µgPt cm
-2
8 A cm-219,000 H2 molecules s-1/Pt site
-2.0 -1.8 -1.6 -1.4 -1.2 -1.0 -0.80.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
= 0.792
= 1.02
Gradient = 0.987
log(Jmax)
log(J@10mV)
log(J@600mV)
log
(JS
pecific /
mA
cm
-2)
log(P(H2) / atm)
0.0 0.2 0.4 0.6 0.8 1.0 1.20
10
20
30
40p(H
2) = 0.013 - 0.001
J Spe
cific
/ m
A c
m-2
E / V vs/ RHE (IR corrected)
Limiting current due to adsorption rate limitation
kad > 4.9 cm s-1 (c.f. kMT > 50 cm s
-1)
-
41
Efc
(V) 1889
1960 1989 2003
2006
L. Mond and C. Langer, Proc. R. Soc. London 46, 296 (1889). W.
Grubb and L. Niedrach, J. Electrochem. Soc. 107, 131 (1960). I.D.
Raistrick, US Patent No. 4876115, 1989. W.L. Gore and Associates,
GORE® PRIMEA® MEAs for Transportation (2003). M.K. Debe et al., J.
Power Sources 161, 1002 (2006).
Advances in performance of polymer electrolyte fuel cells
specific activity
Platinum all over again…
From Michael Eikerling
SFU, Canada
-
Making a fuel cell using these new electrodes
H2 H2
-
Making a fuel cell using these new electrodes
H2
H
2
Nafion Membrane
25 µm
50 µm
-
3-electrode solid state electrochemical cell
Key benefits:
• More representative of a fuel cell MEA
• Variable water activity studies
• Larger temperature range of operation
IrOx Reference
electrode
Counter Electrode
Porous gas diffusion electrode
-
Conclusions
Flow is not fully laminar in a single serpentine flow field
Convective flow is observed in reactant transport media
The term “gas diffusion layer” is incorrect – convection is
important
Electrokinetic functions for the orr and hor reactions have been
generated
A solid state three-electrode cell has been produced
The full fuel cell system is being constructed at the moment
-
Thiago Lopes, Biraj Kakati, Matthew Markiewcz, Chris Zalitis
Johnson Matthey plc, catalysts and discussions (Jonathon
Sharman, Ed Wright)
Intelligent Energy (Paul Adcock, Simon Foster)
EPSRC grants
•EP/G030995/1 Supergen Fuel Cell Consortium;
•EP/K503733/1 Impact Acceleration Research Grant
Acknowledgements
46
