A combined in-situ and post-mortem investigation on local permanent degradation in a direct methanol fuel cell

Abstract

This work proposes a systematic experimental investigation, coupling in-situ diagnostics (electrochemical and mass transport investigation) with ex-situ analyses of pristine, activated and aged components (X-ray photoelectron spectroscopy and transmission electron microscopy), with an in-plane and through-plane local resolution. Such a combined approach allows to identify on one hand the degradation mechanisms, the affected components and the presence of heterogeneities; on the other hand, it allows to quantify the effect of the major mechanisms on performance decay. Thanks to a novel procedure, temporary (0.021 mV/h) and permanent degradation (0.059 mV/h) are separated, distinguishing the latter in different contributions: the effects of active area loss at both at anode (0.009 mV/h) and cathode (0.031 mV/h), mass transport issue (0.015 mV/h) and membrane decay (0.004 mV/h). The post-mortem analysis highlights the effect of degradation mechanisms consistent with the in-situ analysis and reveals the presence of considerable in plane and through plane heterogeneities in: particle size growth in catalyst layers, Pt/Ru and polymer content in catalyst and diffusion layers, Pt/Ru precipitates in the membrane.