Ion exchange capacity controlled biphenol-based sulfonated poly(arylene ether sulfone) for polymer electrolyte membrane water electrolyzers: Comparison of random and multi-block copolymers

Abstract

Conventionally, highly proton conductive perfluorosulfonic acid (PFSA) ionomers are used for an electrolyte membrane in a polymer electrolyte membrane water electrolyzer. As alternatives to the expensive and highly hydrogen permeable PFSA membranes, hydrocarbon-based sulfonated poly(arylene ether sulfone) proton conducting polymers (BPSH) are synthesized by varying their ion exchange capacity (IEC) from 1.2 to 2.0 meq/g, and the way to employ ion conducting units into polymers (random versus block). BPSH membranes show much lower hydrogen permeability (20 − 45 barrer) than that of PFSA membranes (~115 barrer for Nafion) at 80 °C and 100%RH. Random BPSH membranes show slightly higher selectivity of proton to hydrogen than the membranes from multi-block BPSH copolymers at a similar IEC may due to the enhanced hydrogen barrier property by less-developed hydrophilic phase. The best performing random BPSH with the IEC ~ 1.9 meq/g shows better performance (5.3 A/cm2) than the similarly thick (~50 μm) Nafion 212 (4.8 A/cm2) at 1.9 V, but the higher degradation rate (951 μV/h) than Nafion 212 (613 μV/h) at an accelerated stress test with the 360 consecutive alternating current densities of 3 and 0.02 A/cm2, simulating on and off a water electrolyzer.