Effect of Thermal Annealing and Cerium Oxide Nanoparticle Additions on the Stability of Perfluorosulfonic Acid Fuel Cell Membranes

Abstract

Polymer electrolyte membranes based on perfluorosulfonic acid (PFSA) exhibit excellent proton conductivity and thermal stability. However, PFSA membranes remain vulnerable to radical-induced degradation during prolonged fuel cell operation, which compromises long-term membrane integrity. To address this limitation, we investigated a stabilization approach combining thermal annealing and cerium oxide (CeO2) nanoparticle incorporation as a route to improve membrane durability under harsh conditions. Oxidative degradation was simulated using Fenton's test, and membrane durability was assessed through structural and functional analyses before and after oxidative stress exposure. The PFSA membranes examined in this study included Nafion, thermally annealed Nafion, and thermally annealed Nafion incorporating CeO2 nanoparticles. Fluoride ion emission rate analyses, scanning electron microscopy, atomic force microscopy, water uptake measurements, and gas permeability analyses demonstrated that thermal annealing and the incorporation of CeO2 nanoparticles effectively suppressed radical-induced chemical degradation and improved the physical stability of the PFSA membranes. The pore structure, mechanical properties, and proton conductivity of the thermally annealed PFSA membrane containing CeO2 nanoparticles were similar to those before Fenton's test. The results from this study demonstrate that the combination of thermal annealing and incorporation of CeO2 nanoparticles enhances the chemical, structural, and functional stability of PFSA membranes.