Migration of Platinum Under Open Cell Voltage: Effect of the Type of Ionomer Membrane

Abstract

Membrane-electrode assemblies (MEAs) comprising perfluorosulfonic acid (PFSA)-type and sulfonated polyaromatic membranes have been submitted to accelerated ageing under open circuit, and characterised during ageing runs and at end of life to better understand the origins of membrane failure under these conditions. Membrane permeability, reactant gas consumption and water production, as well as the decline in cell voltage, have been monitored with time. Aged MEAs have been characterised using scanning and transmission electron microscopy. We surmise that the origin of failure of PFSA-based MEAs at high cell potential is due to electrochemically-induced platinum dissolution, migration and subsequent progressive in situ reduction of oxidised platinum species to give platinum nanoparticles within the membrane. These dispersed particles, comprising a metallic core and ionic shell, could also act as centres for the generation of free radicals that chemically degrade the membrane, leading to increased porosity, gas crossover and ultimately membrane and MEA failure.