Catalyst Degradation in Fuel Cell Electrodes: Accelerated Stress Tests and Model-based Analysis

Abstract

Catalyst degradation is the major hurdle in the development of polymer electrolyte fuel cells for automotive applications. This article presents an analysis of degradation data obtained in accelerated stress tests under ex situ conditions. The influence of the range of potential variation, potential waveform and temperature on the loss of electrochemical surface area was analyzed. Higher upper potential limit, square waveform of potential cycling, and increased temperature were found to accelerate degradation. A Pt counter electrode affects stress test results because it reaches potentials, at which it dissolves. This effect markedly distorts results for dissolution and redepostion rates at the working electrode; it can be eliminated by using an alternative counter electrode material. Experimental data were analyzed with a dynamic model that couples degradation mechanisms by dissolution/redeposition, coagulation and detachment. Detachment plays a role only at higher potentials (1.2V vs. RHE), at which carbon corrosion of the substrate is strongly enhanced. In this potential range, coagulation and dissolution/redeposition seemingly have a similar impact, in addition to detachment. A square wave potential cycle enhances the contribution of dissolution and redeposition, as compared to a triangular potential cycle. At the lower upper potential limit of 0.9V, degradation was significantly lower. The current analysis does not resolve the ambiguity of coagulation and dissolution/redeposition mechanisms.