Studying Pt-based fuel cell electrode degradation with nanoscale X-ray computed tomography

Abstract

Improvements in Pt-based catalysts and support durability are important to enable mass-market penetration of proton exchange membrane fuel cells (PEMFCs) in the automotive sector. This work focuses on a membrane electrode assembly (MEA) scale analysis of cathode catalyst layer (CCL) degradation processes occurring during catalyst accelerated stability testing (AST). We examined the degradation of the carbon support, decrease in electrochemically active surface area (ECSA), and formation of a platinum (Pt) band. We utilized a combined electrochemical and ex-situ nanoscale X-ray computed tomography (nano-CT) imaging technique to characterize these important degradation processes in state-of-the-art MEAs and examined the effects of AST cycling on two carbon supports, Vulcan (Vu) and a KetjenBlack high surface area carbon (HSC), and two Pt-based catalysts, pure Pt and PtCo. We found that neither support nor catalyst type completely suppressed the formation of a Pt band, but we did find that the PtCo catalyst and HSC support combination was able to limit the ECSA loss and Pt band formation better than the pure Pt and Vu combination. Our results also showed some loss of macroporosity in the HSC support after catalyst AST cycling, helping to explain the reduced performance seen with HSC-supported catalysts at high current densities.