Mechanistic interactions in polymer electrolyte fuel cell catalyst layer degradation

Abstract

Polymer Electrolyte Fuel Cells (PEFCs) exhibit considerable performance decay with cycling owing to the degradation of platinum (Pt) catalysts, resulting in the loss of the valuable electrochemically active surface area. Catalyst inventory retention is thus a necessity for a sustained cathodic oxygen reduction reaction (ORR) and to ameliorate the life expectancy of PEFCs. We demonstrate a thermo-kinetic model cognizant of processes like platinum particle dissolution–reprecipitation and oxide formation coupled with an electrochemical reactive transport model to derive mechanistic insights into the deleterious phenomena at the interfacial scale. The heterogeneous nature of particle aging in a catalyst layer environment is delineated through coarsening–shrinking zones and further comprehension of instability signatures is developed from the dissolution affinity of diameter bins through a metric, onset time. The severe degradation at high temperature and under fully humidified conditions is intertwined with the local transport resistance and the critical transient, where the catalyst nanoparticles reach a limiting diameter stage. We further reveal the degradation-performance characteristics through variation in the ionomer volume fraction and the mean size of the particle distribution in the electrode. It has been found that the kinetic and transport characteristics are crucially dependent on the interplay of two modes – one leading to the depletion of the catalyst nanoparticles and the other that emanates from catalyst coarsening.