Experimental study and modeling of water transport through short-side-chain perfluorosulfonic acid membranes

Perfluorosulfonic acid polymer membranes are state-of-the-art electrolytes in PEMFCs and PEMWEs, and their degradation represents still one of the limiting factor to increase lifetime of electrochemical devices. Due to significant role of water in stressing degradation mechanisms, this work, through an experimental and theoretical analysis, deepens comprehension of materials and constructive properties of short-side-chain (SSC) membranes on dynamic water transport. A systematic analysis is carried out by analysing samples with different membrane thickness and EW, coupled with different gas diffusion layers. A model was adopted to analyse both steady-state and transient water transport tests, evaluating individual contributions to the total water mass transfer. Particular attention was given to swelling/shrinking mechanism, highlighting its strong impact on water sorption and membrane hydration. Membrane diffusion and interfacial mass transfer were independently investigated, identifying their interconnections with material-bulk and superficial properties. Results highlight that membrane with low EW (790 g mol−1), coupled with hydrophilic gas diffusion layers that oppose negligible interfacial resistances to water transport, allows to reduce total resistance by approximately 39% compared to reference configuration (980 g mol−1, hydrophobic).