Microphase-optimized sulfonated poly(biphenyl-piperidine-alkylene)-co-poly(biphenyl-trifluoroacetophenylene) proton exchange membranes with enhanced proton conductivity and oxidative stability for water electrolysis

Abstract

A novel series of sulfonated poly(biphenyl-piperidine-hexylene)-co-poly(biphenyl-trifluoroacetophenone) (SPBPH-TFP-x) proton exchange membranes is synthesized via an amine-alkylation approach, wherein flexible hexylene-tethered sulfonic acid side chains are introduced through hydrophilic piperidine linkers on aromatic backbones without ether linkages. The incorporation of aliphatic pendants promotes well-defined organization of hydrophilic and hydrophobic domains, enabling the formation of continuous proton-conducting pathways. The mobile sulfonic acid groups on the flexible side chains enhance proton transport, whereas the rigid biphenyl backbone imparts high thermal, mechanical, and dimensional stability. Among the fabricated membranes, SPBPH-TFP-70 demonstrates a proton conductivity reaching 0.107 S cm⁻¹ while retaining a mechanical strength of 83.5 MPa at room temperature. In addition, it exhibits superior oxidative stability, retaining over 87.5% of its initial mass after 15 h of exposure to Fenton's solution (3 wt% H₂O₂, 4 ppm Fe²⁺) at 80 °C. Owing to its outstanding properties, the SPBPH-TFP-70 membrane demonstrates excellent performance in a proton exchange membrane water electrolysis cell using platinum-on-carbon catalysts for both electrodes, achieving 6.13 A cm⁻² under an applied voltage of 2.0 V at 90 °C, underscoring its potential as a high-performance proton exchange membrane for hydrogen production.