Universal Correlation between Cathode Roughness Factor and H₂/Air Performance Losses in Voltage Cycling-Based Accelerated Stress Tests

Abstract

The loss of electrochemically active surface area ( ECSA ) in the cathode during load cycling remains a major durability issue for proton exchange membrane fuel cells (PEMFCs). Here, the degradation of low-loaded cathodes (0.1 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">mg</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">Pt</mml:mi> </mml:mrow> </mml:msub> <mml:mspace width=".25em"/> <mml:msubsup> <mml:mrow> <mml:mi mathvariant="normal">cm</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">MEA</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>2</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> ) was investigated by accelerated stress tests (ASTs) in H 2 /N 2 configuration, varying the upper potential limit (UPL, 0.85–1.0 V) and the hold time (1, 2, or 8 s) of the square wave voltage cycling profiles. A full voltage loss analysis was performed at beginning-of-life and after 100, 300, 1 k, 2 k, 5 k, 10 k, 20 k, 50 k, 100 k, 200 k, and 500 k cycles, determining: (i) the roughness factor ( rf ) via CO-stripping; (ii) the H 2 -crossover; (iii) the cathode electrode’s proton conduction resistance; (iv) the H 2 /O 2 and H 2 /air performance; and, (v) the O 2 transport resistance. It was found that the ECSA / rf deteriorates linearly vs the logarithm of the number of cycles or time at UPL, with higher slopes for harsher ASTs. The individual voltage losses were found to be either unaffected by the aging (H 2 -crossover and proton conduction resistance) or depend exclusively on the cathode rf (mass/specific activity and O 2 transport resistances), independent of the AST procedure. This results in a universal correlation between H 2 /air performance and rf during voltage cycling ASTs.

Topics & Concepts