Fabrication Strategy–Induced Modulation of Proton Transport and Interfacial Behavior in Membranes for Electrolysis

Ion exchange membranes play a critical role in proton exchange membrane water electrolysis (PEMWE) by governing hydrogen production efficiency and operational stability. However, conventional Nafion and SPEEK membranes suffer from limitations in permeability and swelling, respectively. In this work, polysulfone (PSf)-based proton exchange membranes were developed using a polyaniline–pyrrole copolymer (PANI–Py) through two different architectures: in situ cross-linking (CR) and mixed-matrix blending (BL). A hydrogen-bonded organic framework (HOF-1) was incorporated to provide additional proton-transport pathways. The in situ cross-linked PSf/PANI–Py membrane exhibited an ion exchange capacity (IEC) of 0.28 mequiv/g at 25 °C, increasing to 0.58 mequiv/g at 80 °C, with a proton conductivity of 2.60 × 10 –4 S/cm. Incorporation of HOF-1 further enhanced proton conductivity to 6.84 × 10 –4 S/cm, attributed to hydrogen-bond-assisted proton hopping within the membrane matrix. Mixed-matrix membranes showed lower IEC and conductivity and significantly higher gas permeability; however, morphological analysis revealed more uniform pore structures and smoother pore walls, thereby improving membrane-electrode interfacial contact, compared with in situ cross-linked membranes. Electrolysis polarization studies indicated that, despite lower intrinsic proton conductivity, the PSf/PANI-Py/HOF(BL) mixed-matrix membrane exhibited significantly improved electrolysis performance compared with the corresponding cross-linked membrane, highlighting the importance of electrochemical properties and interfacial contact for optimal performance.