Characterization of Water Management in PEM Fuel Cells with - PowerPoint PPT Presentation

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 WWW.FCRC.CA

Water management in PEM fuel cell Flooded e e e + e + + + + water content + Water Water Hydrogen Hydrogen + + Oxygen Oxygen e e membrane + catalyst porous transport layer + + + Dry

Microporous Layer (MPL) Porous Transport Layer (PTL) Catalyst Coated Proton Exchange (Gas Diffusion Layer) Membrane (CCM) Membrane (PEM) 200 μ m 200 μ m 1 μ m catalyst layer porous carbon microporous layer backing 2

Effect of MPL on PEMFC performance 1.2 Positive effects of MPL: � reduces cathode flooding 1.0 • U. Pasaogullari, C.-Y. Wang, Electrochim. Acta 4 9 (2004) 4359 • L. R. Jordan, A. K. Shukla, T. Behrsing, 0.8 E cell / V with MPL N. R. Avery, B. C. Muddle, M.Forsyth, PEMFC with MPL J. Power Sources 8 6 (2000) 250 0.6 � im proves catalyst utilization • Z. Qi, A. Kaufman, J. Power Sources , PEMFC without MPL 1 0 9 (2002) 38 0.4 without MPL � Reduces variability in cell perform ance 0.2 • Z. Qi, A. Kaufman, J. Power Sources , 0.0 0.2 0.4 0.6 0.8 1 0 9 (2002) 38 i / A/cm 2 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. D. Malevich, E. Halliop, B. Peppley, J. Pharoah, K. Karan, J. Electrochem. Soc., 156 , B216 (2009) 3

Theories explaining MPL effect MPL Oxygen Oxygen cathode membrane catalyst layer Hydrophobic characteristic of the MPL + + forces w ater from cathode tow ards FFP reducing + + flooding Proposed in: A. Z. Weber and J. Newman, J. Electrochem. Soc. , Water Water 152 , A677 (2005) Porous transport layer (aka GDL) 4

Theories explaining MPL effect cathode MPL Oxygen Hydrogen Oxygen Hydrogen catalyst anode membrane layer catalyst layer water drag with proton + + + + + + water back diffusion Water Water MPL facilitates w ater back diffusion providing better hum idification of m em brane and catalyst layers Proposed in: G. Lin and T. V. Nguyen, J. Electrochem. Soc. , 152 , A1942 (2005). 5

Theories explaining MPL effect MPL Oxygen Oxygen cathode membrane catalyst layer water MPL m akes open pathw ays for gaseous + + oxygen to be transported to catalyst layer + + water water Proposed in: J. T. Gostick, M. A. Ioannidis, M. W. Fowler, M. D. Water Water Porous transport layer (aka GDL) Pritzker, Electrochem. Comm . 11 , 576 (2009) 6

Approaches to examine proposed mechanisms Flow visualization 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) 7

Approaches to examine proposed mechanisms Electrochemical Impedance Spectroscopy (EIS) Setup 1 or Setup 2 V -1 I=V*R s impedance analyser resistance R s EIS enabled potentiostat or potentistat+ impedance analyser electronic load Low-current impedance High-current impedance PEM fuel cell 8

EIS response of PEM fuel cell -0.2 12 Hz 600 Hz 3 Hz 1 Hz Z'' / Ω cm 2 60000 Hz -0.1 0.1 Hz 1 2 3 0.0 0.0 0.1 0.2 0.3 0.4 0.5 0.6 Z' / Ω cm 2 Low- High- Mid-frequency arc High- frequency frequency frequency intercept arc arc 9

Mid-frequency arc: charge transfer resistance effect of current density on EIS response 0.2 210 mA cm -2 2 -Z'' / Ω cm 300 mA cm -2 400 mA cm -2 0.1 500 mA cm -2 R ( i =500) R ( i =210) 0.0 0.0 0.1 0.2 0.3 0.4 0.5 Z' / Ω cm 2 D. Malevich, E. Halliop, B. Peppley, J. Pharoah, K. Karan, J. Electrochem. Soc., 156 , B216 (2009) 10

Low-frequency arc: mass-transport resistance effect of cathode gas on EIS response -0.2 12 Hz 600 Hz 3 Hz Z'' / Ω cm 2 60000 Hz 1 Hz -0.1 H 2 /Air cell 0.0 H 2 /(20%O 2 +He) cell 0.1 Hz 0.0 0.1 0.2 0.3 0.4 0.5 0.6 Z' / Ω cm 2 D. Malevich, E. Halliop, B. Peppley, J. Pharoah, K. Karan, J. Electrochem. Soc., 156 , B216 (2009) 11

High-frequency arc: membrane resistance -0.3 12 Hz Z'' / Ω cm 2 -0.2 24 Hz 2 Hz H 2 /Air cell 1.5 kHz -0.1 60 kHz H 2 /O 2 cell H 2 /H 2 cell 0.1Hz 0.0 0.0 0.1 0.2 0.3 0.4 0.5 0.6 Z' / Ω cm 2 0 0 H2 / H2 E cell -E cell(j=0) / mV E cell -E cell(j=0) / mV -50 -5 D. Malevich, E. Halliop, B. Peppley, J. Pharoah, K. Karan, R=0.1 Ω cm 2 ECS Transactions 156 , 1763 (2008) -10 -100 -150 -15 Diameter of high-frequency arc found to be consistent with the -200 -20 resistance calculated from the H2 / Air -250 -25 known geometry and conductivity of the Nafion membrane -300 -30 0 50 100 150 200 250 300 350 J. M. Le Canut, R. Latham, W. Mérida, D. A. Harrington, J. Power Sources , 192 , 457 (2009) i / mA cm -2 12

EIS response of PEM fuel cell: arc assignment polarization curve E / V total cell resistance (R cell ) R cell -0.2 12 Hz 600 Hz Z'' / Ω cm 2 60000 Hz -0.1 0.1 Hz 3 Hz 1 2 3 i = 0.21 A cm -2 0.0 0.0 0.1 0.2 0.3 0.4 0.5 0.6 Z' / Ω cm 2 In-series resistance Cathode charge- Cathode mass- Membrane (FFP, endplates, transfer resistance transport resistance resistance cables etc.) 13

Effect of MPL on PEMFC EIS response -0.2 12 Hz 600 Hz 3 Hz without MPL Z'' ( Ω cm 2 ) 1 Hz 60000 Hz -0.1 with MPL 0.0 0.1 Hz 0.0 0.1 0.2 0.3 0.4 0.5 0.6 Z' ( Ω cm 2 ) Impedance diagrams for PEMFC with (2,3) and without (1) MPL fed with H 2 / Air. Current density – 0.21 A cm -2 . 14

15 Effect of MPL: influence of current density with MPL 0.7 A cm -2 0.3 A cm -2 without MPL

Equivalent circuit fitting 0.2 2 -Z'' / Ω cm 0.1 0.0 0.0 0.1 0.2 0.3 0.4 0.5 Z' / Ω cm 2 Randles circuit: CPE m CPE dl R o W R ct R m Z w 16

Effect of current density on cathode charge-transfer and Warburg resistances without MPL 0.5 with MPL R ct 0.4 R w 2 R w R / Ω cm 0.3 0.2 0.1 R ct 0.0 300 400 500 600 700 800 900 -2 i / mA cm 0.6 5 R ct +R w 0.5 6 2 R / Ω cm 0.4 R ct +R w 0.3 0.2 300 400 500 600 700 800 900 -2 i / mA cm 17

Time constants for oxygen transport process Experimentally determined: Theoretically predicted: 18

MPL effect models Model A: MPL promotes water back diffusion Model B: MPL forces water to FFP Expected effects: Expected effects: •Increased amount of water in cathode •Reduced amount of water in cathode catalyst layer catalyst layer •Reduced membrane resistance •Increased water content in cathode PTL •Reduced water content in cathode PTL not observed observed 19