Electrochemical impedance study of anode CO-poisoning in PEM fuel cells

In situ Electrochemical Impedance Spectroscopy (EIS) is used as a diagnosti c tool to provide information on the processes responsible for the activity loss of anodes in PEM fuel cells in the presence of CO. The impedance spec tra on Pt and Pt50Ru50 gas diffusion electrodes are presented and compared at various potentials, in an attempt to furnish new criteria for characteri zing the CO tolerance of electrocatalysts. Changes of the EIS pattern as a function of CO concentration, catalyst loading and temperature are also pre sented and discussed comparatively for Pt and PtRu. Arguments are presented to support the hypothesis that the better CO tolerance of PtRu as compared with Pt is mainly determined by a higher ratio between the rates of oxidat ive removal of CO and CO re-adsorption. A new criterion, based on EIS, is p roposed for defining the CO tolerance of electrocatalysts.