Electrons, ions, heat, and fluids: The
complex interplay of properties in porous
electrodes and the porous transport layer
Brant Peppley
Director Queen’s-RMC Fuel Cell Research Centre
CANADIAN TEAM
Queen’s-RMC Fuel Cell Research Centre
Kunal Karan
 Jon Pharoah
 Brant Peppley
NRC-IFCI, Vancouver Group
 Michael Eikerling
 John Stockie
University of Victoria
 Ned Djilali
 Marc Secanell
Univ of Waterloo
 Michael Fowler
 Sumit Kundu
Univ British Columbia
 Fariborz Taghipour
NRC-ICPET, Ottawa Group
 Steven Beale
Electrons, ions, heat, and fluids: The
complex interplay of properties in porous
electrodes and the porous transport layer
Brant Peppley
Director Queen’s-RMC Fuel Cell Research Centre
Macro-water management in PEM fuel cell
Flooded
e
e
e
e
+
+
+
Hydrogen
+
Water
Water
+
+
Oxygen
Oxygen
water content
+
+
e
e
membrane
catalyst
porous transport layer
+
+
+
+
Dry
Processes, Operating Parameters
and Effects
Catalyst
Layer
PEFC Key Sub-Components
Flow-Field
Gas Diffusion
Media
Interface
Properties
Species
Transport
Composition
&
Microstructure
Electrochemical
Kinetics
Bulk
Properties
Overall
Performance
•
•
Operating Conditions
P, T, PO2, PH2, RH, Stoich Ratio
Configuration
V-I Curves
Water Transport
Need for Gas Diffusion Media Optimisation
+
Considerations of 2-D and 3-D Effects
Current Density (A/m 2)
2-D Effects: Current Density Distributions
1400
1350
1300
1250
1200
1150
0.0
7000
0.2
0.4
0.6
0.8
1.0
6800
Channel
6600
Land
6400
GDL
6200
6000
0.0
0.2
0.4
0.6
0.8
1.0
0.2
0.4
0.6
0.8
1.0
Catalyst Layer
11500
10500
9500
8500
7500
0.0
Sun, W., Peppley, B.A.P. and Karan, K. (2005)
Electrochimica Acta, 50 (16-17), 3359-3374.
S. A. Freunberger et al. Electrochem. Comm.
8, (9), 2006, 1435-1438
Carbon Paper is Inherently Anisotropic !!
Current Density (A/cm2)
Influence of GDL Conductivity
A
4000
3900
3800
orthotropic
3700
A
3600
3500
h=0.4V
3400
3300
0.0
0.2
0.4
0.6
0.8
1.0
Current Density (A/cm2)
B
7400
7200
h=0.5V
7000
6800
orthotropic
6600
B
6400
6200
6000
5800
0.0
0.2
0.4
0.6
Channel
0.8
1.0
Land
Isotropic
In-plane conductivity = Through-plane conductivity
Orthotropic
GDL
In-plane conductivity = 10  (Through-plane conductivity)isotropic
Catalyst Layer
J.G. Pharoah, K. Karan, and W. Sun. (2006)
J. Power Sources 161 (1), 214-224, 2006.
3D Effects: Straight Versus Serpentine Flow Fields
3D Effects – Influence of GDM Permeability
Maximum
current under
the channel
Location of
maximum
current
varies with
PTL
permeability
3D Effects: Mass Transport/Convection in Channel and GDM
•The flow in the
channel is greatly
reduced due to
convection in the
PTL
•The secondary
flow structures are
greatly altered due
to this mechanism
•Very significant for
•Transition to
unsteady flow
• Liquid
transport
3D Effects: Water Accumulation in Serpentine Flow Channels
Water is most often
found in the bends!
Neutron Imaging Data
Courtesy of David
Jacobsen, NIST
FCRC Expertise/Capabilities
•
2D and 3D Computational Fluid Dynamics (CFD) Calculations
•
Numerical Effective Transport Property Estimation
Permeability Estimation
(Lattice Boltzmann Method)
Effective Conductivity Estimation
T
1
T
q”
2
Mark Vandoormal, MSc Thesis, Queen’s University
Dan Hamilton, MSc Thesis, Queen’s University
GDM Characterisation - FCRC Expertise/Capabilities (cont.)
•
Experimental Characterisation of GDM
– Permeameter (Gas and Liquid Permeability)
– Porometer (Hydrophobic and Hydrophilic Pores)
– In-Situ Effective Permeability Measurement
Brian Tysoe, MSc Thesis, Queen’s University
CONCLUSION-1:
GDM Can Strongly Affect FC Performance !!
RECOMMENDATION-1:
Proper Characterisation of GDM Transport and
Physical Properties is Essential
Catalyst
Layer
FC Sub-Components
(geometry/material)
Flow-Field
Gas Diffusion
Media
Interface
Properties
Species
Transport
Composition
&
Microstructure
Electrochemical
Kinetics
Bulk
Properties
Overall
Performance
•
•
Operating Conditions
P, T, PO2, PH2, RH, Stoich Ratio
Configuration
V-I Curves
Water Transport
Need for Catalyst Layer Optimisation
Cathode Agglomerate Model: Effectiveness Factor
Channel
Land
GDL
z
Catalyst Layer
x
Underutilized core of
catalyst agglomerate
O2 diffusion
path
Sun, W., Peppley, B.A.P. and Karan, K. (2005)
Electrochimica Acta, 50 (16-17), 3359-3374.
Anode Agglomerate Model: Transport Limitations at Two-Scales
100000
1.0
0.1 mV
0.8
0.01 mV
CH2/CH2,s
0.1 mV
0.6
0.5 mV
1 mV
0.4
5 mV
10 mV
0.2
0.0
Rate of H2 Consumption (mol/cm2-s)
90000
0.5 mV
80000
1.0 mV
70000
5.0 mV
60000
10 mV
50000
40000
30000
20000
10000
0
0.2
0.4
0.6
0.8
1
0
0
r/ragg
2
4
6
8
10
Distance along catalyst layer (mm)
Underutilized
core of catalyst
agglomerate
ragg
Only 40% of the outer core of the agglomerate is active
Only 30% of the catalyst layer is utilized
K. Karan (2007) Electrochem Comm. 9, 747-753;
K. Karan Structural Modeling of PEMFC Anodes. 211th ECS Meeting - Chicago, Illinois, May 6-11, 2007
Catalyst Layer Optimisation
M. Secanell, K. Karan, A. Suleman and N. Djilali (2007) Electrochimica Acta, 52, 22, 6318-6337.
3D Catalyst Layer Modeling
Slide Water
title in Catalyst Layer
Other Effects of Liquid
Porous Transport Layer
Catalyst Layer
Membrane
ionomer
platinum particle (2-3 nm)
carbon particle (~40 nm)
secondary pore
agglomerate (~ ?? nm, ~ particles)
primary pore
Ionically insulated agglomerate due to
ionomer contraction (drying)
Poor ionic conductivity due to imbalanced
water drag and water back diffusion (anode)
water back
diffusion
water drag
Electronically insulated agglomerate due
to ionomer expansion (water intake)
Detection: decrease in ESA*
decrease in electronic conductivity
Detection: decrease in ESA*
decrease in ionic conductivity
*ESA – electrochemically active surface area
Detection: little to none decrease in ESA*
decrease in ionic conductivity
FCRC-NRC Capabilities
•
Microstructural Modeling
– NRC-IFC
– FCRC
•
CCL Optimisation
– U. Victoria
•
Catalyst Layer Properties
– FCRC
•
Catalyst Preparation
– FCRC
– NRC-IFCI
Catalyst Layer Preparation
Dimatix DMP2800 material printer
Nafion-112 membrane
1 mm
printed
catalyst layer
Fabrication of Catalyst Layer of
Controlled Composition
and Microstructure (?)
Carbon paper with
microporous layer
1 mm
Slide(ESA)
title measurement: cyclic voltammetry
Electrochemically active surface area
Potentiostat
counter&reference
electrode
Nitrogen
-
-SO3 + PtH
-1e-
-2ePt + H2O
PtO + 2H+
-SO3H + Pt
1.0
0.5
working electrode
0.0
I/A
Hydrogen
1.5
-0.5
-1.0
-SO3H + Pt
-1.5
2(-SO3H)
-2.0
0.0
0.1
+2e-
0.2
+1e-
-SO3- + PtH
2(-SO3-) + H2
0.3
0.4
E/V
0.5
0.6
0.7
0.8
0.9
title
Electronic conductivitySlide
of catalyst
layer in PEM fuel cell

platinum wires
Teflon mesh
porous
transport
layer
catalyst layer
membrane
platinum wire
 *d
ln 2
*
R
AB ,CD
 RBC , DA   RAB,CD 

f 

2
 RBC , DA 
title layer in PEM fuel cell
Ionic conductivity ofSlide
catalyst
Electrochemical Impedance Spectroscopy of PEM fuel cell
oxygen gas
phase diffusion
Z''
ohmic
resistance anode cathode charge transfer
porous
transport
layers
0
Rohm
membranes
RpA
RpC
Z'
Catalyst layers
CPEC
CPEA
=
WC
CONCLUSION-2
Transport and kinetics in catalyst layer strongly influence FC
performance and water transport
RECOMMENDATION-2
Proper characterisation (microstructural and transport
properties) and modeling of catalyst layer is key to optimising
FC performance and water transport
Micro-Porous Layer (MPL) as
a Catalyst Layer-Gas Diffusion Media Interface:
Need for MPL Optimisation
PEMFC with Microporous Layers (MPLs)
Porous Transport Layer (PTL)
(gas diffusion layer)
Catalyst Coated
Membrane (CCM)
Proton Exchange
Membrane (PEM)
Not to scale
200mm
porous carbon
backing
200mm
microporous layer
1mm
catalyst layer
Role of MPL on Water Transport: Two Schools of Thoughts
Anode
CL
Membrane Cathode MPL Porous
CL
Carbon
Backing
water drag with
proton
+
+
+
+
+
+
Water
water back diffusion
MPL retains liquid water in Cathode CL and aids back diffusion MPL helps remove water from Cathode CL to Cathode GDM
• J.H. Nam, M. Kaviany, Int. J. Heat Mass Transfer, 46
(2003) 4595-4611.
• U. Pasaogullari, C.-Y. Wang, Electrochim. Acta, 49
(2004) 4359-4369.
• A.Z. Weber, J. Newman, J. Electrochem. Soc., 152 (2005)
A677-A688.
• G. Lin, T.V. Nguyen, J. Electrochem. Soc., 153 (2006)
A372-A382.
Effect of MPL on Water Drag
H. K. Atiyeh, K. Karan, B. Peppley, A. Phoenix, E. Halliop and J. Pharoah (2007) J. of Power Sources, 170, 1, 111-K.
Karan, H. Atiyeh, E. Halliop, A. Phoenix, B. Peppley, J. Pharoah, (2007) Electrochem Solid State Lett. 10, 2, B34-B38.
Effect of MPL on Electrochemical Perfomance & Durability
Cells with no MPLs
Cells with MPL on at least one side
H. K. Atiyeh, K. Karan, B. Peppley, A. Phoenix, E. Halliop and J. Pharoah (2007) J. of Power Sources, 170, 1, 111
K. Karan, H. Atiyeh, E. Halliop, A. Phoenix, B. Peppley, J. Pharoah, (2007) Electrochem Solid State Lett. 10, 2, B34
MPL Reduces Fluoride Release Rate !!
5.0
Fluoride Release Rate (umol h-1)
Anode
Cathode
4.0
Total
3.0
Thinned
Membrane
!!
MPL on anode only
2.0
1.0
0.0
Total Fluoride Release Rate (umol h-1)
250
350
450
550
Current Density (mA cm-2)
650
750
Anode
Cathdoe
0.10
Total
0.05
MPL on cathode and anode
0.00
250
350
450
550
Current Density (mA cm-2)
650
750
S. Kundu, K. Karan, M. Fowler, L C Simon, B A Peppley, and E. Halliop, (Accepted Nov 2007). Influence of
Micro-porous Layer and Operating Conditions on the Fluoride Release Rate and Degradation of PEMFC
Membrane Electrode Assemblies, Journal of Power Sources.
Single Cell Impedance Response – With and Without MPL
-0.2
12 Hz
2
Z'' ( cm )
600 Hz
-0.1
3 Hz
1 Hz
60000 Hz
3
0.0
2
1
0.1 Hz
0.0
0.1
0.2
0.3
0.4
Z' ( cm2)
0.5
0.6
Impedance diagrams for PEMFC with (2,3) and without (1) MPL fed with
H2/Air (1,2) and H2/(20%O2 in He) (3). Current density – 0.21 A cm-2.
Impedance Modeling Example: Porous SOFC Cathode (LSM/YSZ)
Step 1.
Step 2.
Step 3.
Step 4.

dCO2
dt
 D eff
d 2CO2
dx 2
 Rads
Rads  kads PO2 Cs2  kdesCO2ads
2
d
COads
dCOads
eff
 DOads
R
dt
dx 2
dCOads
 k f COa d sCVO  kbCOo Cs
dt
Impedance Model – Comparison with Experimental Data
|Z| (ohm cm2)
1.4
-0.50
Experimental
-0.40
Faradaic impedance
1.0
0.8
0.6
0.4
0.2
0.0
0.1
Model
Z" (ohm cm2)
1.2
10
-0.30
1000
100000
Freq (Hz)
-0.20
0.00
0.80
0.90
1.00
1.10
Z' (ohm cm2)
1.20
1.30
Phase (Hz)
-0.10
-9
-8
-7
-6
-5
-4
-3
-2
-1
0
1
0.1
10
1000
100000
Freq (Hz)
DOeff2 N 2  2.7 10 5 m 2 /s
k ads  1.9 108 m 2 /atm - mol - s
eff
DOads
 9.3  10 9 m 2 /s
k des  7.8 108 m 2 /atm - mol - s
k f  5.7 102 m4 /mol - s
kb  2.8 1/s
Zf - DO2-N2/10
Zf - DO2-N2/100
Phase (deg)
Z" (ohm cm2)
Gas Diffusivity
Effect
-1.0
-0.9
-0.8
-0.7
-0.6
-0.5
-0.4
-0.3
-0.2
-0.1
0.0
Zf - DO2-N2
1
1.2
1.4
1.6
1.8
2
Z' (ohm cm2)
-0.60
Zf - DOads/10
-14
Zf - DOads/100
-12
Zf - DOads
-10
-0.20
1
1.2
-1.00
1.4
1.6
Z' (ohm cm2)
1.8
Zf - DO2-N2
10
1000
100000
Zf - DOads/10
Zf - DOads/100
Zf - DOads
-8
-6
-4
-0.60
-0.40
-0.20
1.2
1.4
1.6
1.8
Z' (ohm cm2)
Freq (Hz)
1000
100000
Zf - kads/kdes/10
Zf - kads/kdes/100
Zf - kads/kdes
-10
-8
-6
-4
-2
0
0.1
0.00
1
10
-12
Zf - kads/kdes/10
Zf - kads/kdes/100
Zf - kads/kdes
-0.80
0
0.1
2
Phase (deg)
Z" (ohm cm2)
Zf - DO2-N2/100
-2
0.20
Absorption/Desorption
Rate Constant Effect
Zf - DO2-N2/10
Freq (Hz)
Phase (deg)
Surface Diffusivity
Effect
Z" (ohm cm2)
-1.00
-20
-18
-16
-14
-12
-10
-8
-6
-4
-2
0
0.1
10
1000
2
Freq (Hz)
100000
CONCLUSION-3
 Interfaces and interfacial layers (MPL) play a crucial role in
water transport
 MPL can reduce membrane degradation !!
 Impedance modeling can help identify MPL’s role in water
transport
RECOMMENDATION-3
 Proper characterisation (microstructural and transport
properties) and modeling of MPL effects is important
 Optimisation of MPL is required for
– improved water management
– reduced membrane degradation
Project partners & their tasks
• Novel GDL,MPL
• Surface properties (ESEM)
• Application to stacks
• Free surface flow in GDL/BPP
• Robust design optimization
• Microfluidic ex-situ experiments
• Modeling at cell level
• Mixed wettability characterization (exp.)
• Structure property relation CL, MPL
• Neutron imaging
• Two-phase catalyst layer modeling, Interface conditions
•
• Microstructural Catalyst Layer Modeling
• 2D and 3D CFD Modeling of Half and Unit Cells
• Numerical & Experimental Characterization of GDL and CL
Properties
• Impedance Characterizarion – Experimental & Simulation
• MPL Characterisation
• Mathematical Optimisation (Collaboration with UVic)
Network of collaboration
• Surface data (ESEM)
• Modified GDLs, MPLs
• Optimized design (GDL,BPP)
• Surface modified BPPs (plasma etching)
Interface conditions
NI analysis
• stacks incl. novel
GDL&BPP
• re-structured GDLs
GDL
wettability
data
Interface conditions
NI analysis
MPL/CL properties
• GDL/MPL/CL Property
Characterisation (Numerical &
Simulation)
• CL Modeling
• Impedance Characterisation
and Modeling
• Mathematical Optimisation
Free surface model
GDL/channel
GDL
wettability
data