Investigation of cathode catalyst layer interfaces evolution during accelerated stress tests for polymer electrolyte fuel cells

To elucidate the evolution of ionomer-Pt and ionomer-carbon interfaces during life cycle of polymer electrolyte fuel cells (PEFCs), electrodes with high surface area (HSA) and durable carbon supports underwent catalyst and carbon corrosion accelerated stress tests (ASTs) under stoichiometric and sub-stoichiometric gas flow conditions. Electrochemical characterizations, as well as X-ray photoelectron spectroscopy (XPS) were utilized to assess degree of components degradation. Catalyst AST results revealed that Pt nanoparticles dispersed within the micro- and meso-pores and not in contact with ionomer are the main contributor to the 50% electrochemical surface area (ECSA) loss observed after 30k cycles resulting in significant polarization loss, which is much more notable in the case of sub-stoichiometric operating condition. Support AST results for HSA carbon showed severe ionomer degradation and 55% ECSA loss within the first 100 cycles, while cell with durable support exhibited negligible polarization and ECSA decay during the first 2500 cycles attributed to higher ionomer coverage, preservation of proton pathways preventing Pt from detachment.