Oxidation resistant cerium oxide styrene-ethylene-propylene-styrene (SEPS) composite anion exchange membranes for water electrolysis

This study reports oxidation-resistant composite anion exchange membranes (AEMs) based on quaternised styrene–ethylene–propylene–styrene (QSEPS) ionomers reinforced with porous PTFE (1 μm pore size, 70 % porosity) and stabilised using cerium oxide (CeO₂) nanoparticles as regenerative radical scavengers. Ex-situ Fenton tests confirmed that CeO₂ effectively mitigates oxidative degradation, with the QSEPS/PTFE composite containing 6 wt% CeO₂ retaining 87 % of its weight after 30 h at room temperature, compared with the complete degradation of the CeO₂-free QSEPS membrane under the same conditions. The improved stability was accompanied by a modest reduction in hydroxide conductivity in deionised (DI) water as QSEPS/CeO₂(6 wt%)/PTFE only reached 0.035 S cm⁻¹ at 60 °C compared with 0.048 S cm⁻¹ for QSEPS/PTFE. However, this conductivity penalty was largely mitigated using 0.1 M KOH supporting electrolyte, where the area specific resistance (ASR) decreased from 0.339 to 0.148 Ω cm² for QSEPS/CeO₂(6 wt%)/PTFE and from 0.222 to 0.115 Ω cm² for QSEPS/PTFE. Long-term durability tests under DI water circulation at 2 V and 60 °C showed markedly improved performance retention with QSEPS/CeO₂(6 wt%)/PTFE exhibiting a 34.9 % current density loss over 900 h compared with 59.1 % for its CeO₂-free counterpart, QSEPS/PTFE, corresponding to degradation rates of 147 and 314 μA cm⁻² h⁻¹, respectively. The results demonstrate that CeO₂ nanoparticles can effectively suppress hydroxyl-radical-induced degradation, thereby extending AEM lifetime under water electrolyser conditions.