XPS analysis of carbon-supported platinum electrodes and characterization of CO oxidation on PEM fuel cell anodes by electrochemical half cell methods

Abstract

An analysis using X-ray induced photoelectron spectroscopy (XPS) on an as received, 20 weight percent (wt.%) Pt/C electrode (E-TEK) indicates the presence of a nanometer thin layer of polytetrafluorethylene (PTFE) on the surface which degrades during potentiodynamic cycling from 0 to 1.5 V RHE. Half cell measurements verify this observation by exhibiting an increase in the transferred charge and thus active surface area. An electrode manufactured by a rolling process containing 20 wt.% Pt/C on a carbon cloth (catalysts powders and cloth from E-TEK) did not have such a layer according to XPS analysis or exhibit such behavior during electrochemical, potentiodynamic cycling. In addition, cyclic voltammetry in a half cell was used to characterize CO oxidation on these two electrodes in addition to one consisting of 20 wt.% Pt–Ru/C catalyst on a carbon backing also produced by the rolling process. Measurements in 0.5 M H 2 SO 4 electrolyte of rotating disk electrodes (RDEs) show recognizable CO oxidation during stripping experiments at potentials comparable to those shown by smooth electrodes, although peak definition for supported electrodes is highly inferior. The labyrinth nature of the pore systems of supported electrodes complicated stripping measurements and called into question the benefit of using RDEs for porous electrodes due to undefinable mass transport conditions within the electrode.