Membrane and Active Layer Degradation upon PEMFC Steady-State Operation: I. Platinum Dissolution and Redistribution within the MEA

Abstract

We studied proton exchange membrane fuel cell membrane electrode assemblies (MEAs) degradation after fuel-cell operation. Anode and cathode pronounced degradation was monitored by chemical [energy dispersive spectrometry (EDS), X-ray photoelectron spectroscopy (XPS)], physical [scanning electron microscopy (SEM), transmission electron microscopy], and electrochemical (ultramicroelectrode with cavity) techniques. Aged MEAs underwent severe redistribution of most elements (Pt, C, F), coupled to a dramatic change of Pt particles shape, mean particle size and density over the carbon substrate. Among the various scenarios for Pt redistribution, Pt dissolution into species and transport in the ionomer or the proton exchange membrane play important roles. The dissolution/transport is likely favored by activators/ligands (F- or -containing species) originating from the alteration of the polymers contained in the MEA. From SEM observations, the source of species is the cathode, while EDS and XPS show some - and F-containing species origin from the anode. Local chemical analyses (SEM-EDS and XPS) revealed the excess Pt monitored in aged MEAs is associated with F excess. For instrumental limitation concerns, we could not detect the S element, but -containing species could also act as counter ions during transport within the MEA. Pt corrosion/redistribution is associated with the decrease of Pt-active area as revealed by -stripping voltammograms.