Carbon corrosion resistance in PEM fuel cells: Comparative study of short and long side chain perfluorosulfonic acid ionomers

This study investigates the degradation mechanisms of catalyst carbon support in proton exchange membrane fuel cells (PEMFCs) employing Nafion® and Aquivion™ ionomers. Through the integration of electrochemical techniques, microscopy, and spectroscopy, the research assesses the impact of ionomer selection on catalyst layer durability (CL) and performance under accelerated stress testing (AST). Post-AST electrochemical analysis reveals significant losses in electrochemically active surface area (ECSA) and catalytic activity for both CLs with the two different ionomers, primarily driven by Pt particle growth, migration, detachment, and carbon support corrosion within the cathode CLs. Structural evaluations using field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) demonstrate considerable thinning and deterioration of cathode CLs, highlighting carbon corrosion and Pt particle agglomeration as key degradation mechanisms. Confocal micro-Raman spectroscopy offers deeper insights into carbon corrosion behavior, showing more pronounced oxidative degradation markers in the cathode CL with Aquivion™ compared to that with Nafion®. Despite this, PEMFCs utilizing Aquivion™ exhibit superior electrochemical performance after 5000 AST cycles, particularly at high current densities. This unexpected improvement is attributed to Aquivion™'s superior proton conductivity even after the AST compared to Nafion®, which helps mitigate mass transport limitations and maintain effective ionomer-catalyst interactions even in the presence of carbon corrosion. These findings underscore the intricate relationship between ionomer properties, carbon degradation mechanisms, and PEMFC performance. They provide critical insights for optimizing ionomer selection to enhance fuel cell durability and efficiency.