Modelling and performance optimisation of proton exchange membrane water electrolyzer considering ionomer swelling

Proton exchange membrane water electrolyzer decomposes water into oxygen and hydrogen using electrical energy as the driving force. During the water electrolysis process, the anode catalyst layer is a key factor influencing the performance of the electrolyzer. Based on the initial structural parameters of the proton exchange membrane water electrolyzer, this study establishes a one-dimensional electrolysis model to investigate the effect of ionomers in the anode catalyst layer on the operational performance of electrolyzer. Six ionomers with different equivalent weights, including both long-chain and short-chain types, were compared. Proton conductivity of ionomers was corrected based on their equivalent weights, and interfacial contact resistance at different ionomer contents was calculated using the constriction resistance theory. Since excessive ionomer in the catalyst layer can cover the active sites of catalyst, there exists an optimal ionomer content in the anode catalyst layer. When using different types of ionomers, the optimal ionomer content varies due to differences in water absorption, which is related to the porosity of the catalyst layer after ionomer water absorption and swelling. Based on this, a formula related to the optimal porosity is proposed in this paper. Furthermore, the performance of short-chain ionomer consistently outperforms that of long-chain ionomer both before and after water absorption and swelling, which demonstrates the advantages of short-chain ionomers. This study can provide references for the optimal design of catalyst layer in proton exchange membrane water electrolyzer.