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Characterization of Water Management in PEM Fuel Cells with Microporous Layer

Using Electrochemical Impedance Spectroscopy

Dzmity Malevich, Ela Halliop, Kunal Karan, Brant A Peppley and Jon Pharoah

Water management in PEM fuel cell

Hydrogen

Oxygen

WaterHydrogen

+

+

+

+Oxygen

Water

membranecatalyst

porous transport layer

e e

+

+++

e e

+

+++

e e

wa

ter

co

nte

nt

Flooded

Dry

Microporous Layer (MPL)

2

porous carbon backing

microporous layer catalyst layer

200μm200μm 1μm

Proton Exchange Membrane (PEM)

Porous Transport Layer (PTL) (Gas Diffusion Layer)

Catalyst Coated Membrane (CCM)

Effect of MPL on PEMFC performance

3

i / A/cm20.0 0.2 0.4 0.6 0.8

E cell / V

0.2

0.4

0.6

0.8

1.0

1.2

PEMFC with MPL

PEMFC without MPL

with MPL

Polarization curves for PEMFCs without MPL and with MPL on anode and cathode sides. Error bars represent standard deviation within batch of identically built cells.

without MPL

Positive effects of MPL:

reduces cathode flooding•U. Pasaogullari, C.-Y. Wang, Electrochim. Acta 49 (2004) 4359

•L. R. Jordan, A. K. Shukla, T. Behrsing, N. R. Avery, B. C. Muddle, M.Forsyth, J. Power Sources 86 (2000) 250

improves catalyst utilization•Z. Qi, A. Kaufman, J. Power Sources, 109 (2002) 38

Reduces variability in cell performance

•Z. Qi, A. Kaufman, J. Power Sources, 109 (2002) 38

D. Malevich, E. Halliop, B. Peppley, J. Pharoah, K. Karan, J. Electrochem. Soc., 156, B216 (2009)

Theories explaining MPL effect

Water

4

+

+

OxygenOxygen

Water

membrane

+

+

MPLcathodecatalyst

layer

Hydrophobic characteristic of the MPL forces water from cathode towards FFP reducing flooding

Porous transport layer (aka GDL)A. Z. Weber and J. Newman, J. Electrochem. Soc., 152, A677 (2005)

Proposed in:

Theories explaining MPL effect

Water

5

HydrogenHydrogen

+

+

+ +

+

+

OxygenOxygen

Water

membrane

water drag with proton

water back diffusion

MPL

G. Lin and T. V. Nguyen, J. Electrochem. Soc., 152, A1942 (2005).Proposed in:

MPL facilitates water back diffusion providing better humidification of membrane and catalyst layers

anodecatalyst

layer

cathodecatalyst

layer

Theories explaining MPL effect

Water

6

+

+

OxygenOxygen

Water

membrane

+

+

MPLcathodecatalyst

layer

MPL makes open pathways for gaseous oxygen to be transported to catalyst layer

Porous transport layer (aka GDL)

Proposed in:

water

water

water

J. T. Gostick, M. A. Ioannidis, M. W. Fowler, M. D. Pritzker, Electrochem. Comm. 11, 576 (2009)

Approaches to examine proposed mechanismsFlow visualization

7

Neutron radiographs of water distribution in flow field channels – effect of PTL (J.P. Owejan, T.A. Trabold, D.L. Jacobson, M. Arif, S.G. Kandlikar, Int. J. Hydrogen Energy, 32, 4489 (2007)

Approaches to examine proposed mechanisms

8

Electrochemical Impedance Spectroscopy (EIS)Setup 1 or Setup 2

resistance Rs

I=V*Rs-1

EIS enabled potentiostat or potentistat+ impedance analyser

impedance analyser

V

electronic load

PEM fuel cell

High-current impedance Low-current impedance

EIS response of PEM fuel cell

9

Z' / Ω cm20.0 0.1 0.2 0.3 0.4 0.5 0.6

Z'' /

Ω c

m2

-0.2

-0.1

0.0123

0.1 Hz1 Hz

3 Hz12 Hz

600 Hz

60000 Hz

High-frequency

arc

Low-frequency

arc

Mid-frequency arcHigh-frequency intercept

Z' / Ω cm2

0.0 0.1 0.2 0.3 0.4 0.5

-Z'' /

Ω c

m2

0.2

0.1

0.0

210 mA cm-2

300 mA cm-2

400 mA cm-2

500 mA cm-2

Mid-frequency arc: charge transfer resistance

10

R(i=500)

R(i=210)

effect of current density on EIS response

D. Malevich, E. Halliop, B. Peppley, J. Pharoah, K. Karan, J. Electrochem. Soc., 156, B216 (2009)

Low-frequency arc: mass-transport resistance

11

Z' / Ω cm20.0 0.1 0.2 0.3 0.4 0.5 0.6

Z'' /

Ω c

m2

-0.2

-0.1

0.00.1 Hz

1 Hz

3 Hz12 Hz

600 Hz

60000 HzH2/Air cell

H2/(20%O2+He) cell

effect of cathode gas on EIS response

D. Malevich, E. Halliop, B. Peppley, J. Pharoah, K. Karan, J. Electrochem. Soc., 156, B216 (2009)

-30

-25

-20

-15

-10

-5

0

0 50 100 150 200 250 300 350-300

-250

-200

-150

-100

-50

0H2 / H2

H2 / Air

Z' / Ω cm2

0.0 0.1 0.2 0.3 0.4 0.5 0.6

Z'' /

Ω c

m2

-0.3

-0.2

-0.1

0.0

1.5 kHz

24 Hz

12 Hz

2 Hz

60 kHz

0.1HzH2/O2 cell

H2/Air cell

H2/H2 cell

High-frequency arc: membrane resistanceE

cell-E

cell(

j=0)

/ m

V

Ece

ll-Ece

ll(j=

0) /

mV

i / mA cm-2

R=0.1 Ω cm 2

12

Diameter of high-frequency arc found to be consistent with the resistance calculated from the known geometry and conductivityof the Nafion membrane

J. M. Le Canut, R. Latham, W. Mérida, D. A.Harrington, J. Power Sources, 192, 457 (2009)

D. Malevich, E. Halliop, B. Peppley, J. Pharoah, K. Karan, ECS Transactions 156, 1763 (2008)

Z' / Ω cm20.0 0.1 0.2 0.3 0.4 0.5 0.6

Z'' /

Ω c

m2

-0.2

-0.1

0.0123

0.1 Hz3 Hz

12 Hz600 Hz

60000 Hz

13

In-series resistance (FFP, endplates, cables etc.)

Membrane resistance

Cathode charge-transfer resistance

Cathode mass-transport resistance

EIS response of PEM fuel cell: arc assignment

total cell resistance (Rcell)

polarization curve

Rcell

E / V

i = 0.21 A cm-2

Effect of MPL on PEMFC EIS response

14

Z' (Ω cm2)0.0 0.1 0.2 0.3 0.4 0.5 0.6

Z'' (Ω

cm

2 )

-0.2

-0.1

0.00.1 Hz

1 Hz3 Hz

12 Hz600 Hz

60000 Hz

Impedance diagrams for PEMFC with (2,3) and without (1) MPL fed with H2/Air. Current density – 0.21 A cm-2.

without MPL

with MPL

Effect of MPL: influence of current density

15

without MPL

with MPL

0.3 A cm-2

0.7 A cm-2

Z' / Ω cm2

0.0 0.1 0.2 0.3 0.4 0.5

-Z''

/ Ω c

m2

0.2

0.1

0.0

Equivalent circuit fitting

16

W

RoCPEm

Rct

CPEdl

ZwRm

Randles circuit:

i / mA cm-2300 400 500 600 700 800 900

R / Ω

cm

2

0.0

0.1

0.2

0.3

0.4

0.5

65

i / mA cm-2300 400 500 600 700 800 900

R / Ω

cm

2

0.2

0.3

0.4

0.5

0.6

Effect of current density on cathode charge-transfer and Warburg resistances

Rw

Rct Rw

Rct

Rct+Rw

Rct+Rw

17

with MPL

without MPL

Time constants for oxygen transport process

18

Experimentally determined:

Theoretically predicted:

MPL effect models

19

Model A: MPL promotes water back diffusion Model B: MPL forces water to FFP

Expected effects:•Increased amount of water in cathode catalyst layer•Reduced membrane resistance•Reduced water content in cathode PTL

Expected effects:•Reduced amount of water in cathode catalyst layer•Increased water content in cathode PTL

observednot observed