XPS ANALYSIS OF CARBON-SUPPORTED PLATINUM-ELECTRODES AND CHARACTERIZATION OF CO OXIDATION ON PEM FUEL-CELL ANODES BY ELECTROCHEMICAL HALF CELL METHODS

An analysis using X-ray induced photoelectron spectroscopy (XPS) on an as received, 20 weight percent (wt.%) Pt/C electrode (E-TEK) indicate s the presence of a nanometer thin layer of polytetrafluorethylene (PT FE) on the surface which degrades during potentiodynamic cycling from 0 to 1.5 V RHE. Half cell measurements verify this observation by exhi biting an increase in the transferred charge and thus active surface a rea. An electrode manufactured by a rolling process containing 20 wt.% Pt/C on a carbon cloth (catalysts powders and cloth from E-TEK) did n ot have such a layer according to XPS analysis or exhibit such behavio r during electrochemical, potentiodynamic cycling. In addition, cyclic voltammetry in a half cell was used to characterize CO oxidation on t hese two electrodes in addition to one consisting of 20 wt.% Pt-Ru/C c atalyst on a carbon backing also produced by the rolling process. Meas urements in 0.5 M H2SO4 electrolyte of rotating disk electrodes (RDEs) show recognizable CO oxidation during stripping experiments at potent ials comparable to those shown by smooth electrodes, although peak def inition for supported electrodes is highly inferior. The labyrinth nat ure of the pore systems of supported electrodes complicated stripping measurements and called into question the benefit of using RDEs for po rous electrodes due to undefinable mass transport conditions within th e electrode. (C) 1998 Elsevier Science S.A. All rights reserved.