Cystine-functionalized MXene/OPBI composite membranes enabling simultaneous enhancement of proton conductivity and oxidative stability for high-temperature fuel cells

Cystine-functionalized MXene (MC)/poly(ether-benzimidazole) (OPBI) composite membranes were developed for high-temperature proton exchange membrane fuel cells (HT-PEMFCs). The functionalization was confirmed by XPS and FTIR. The optimal OPBI/MC-15 membrane exhibited an acid doping level of 27.8 and proton conductivity of 163.7 mS cm −1 at 180 °C under anhydrous conditions, which was 2.8-fold higher than that of pristine OPBI. The disulfide (S–S) moieties served as effective radical scavengers, enabling exceptional oxidative stability for the composite membranes. Specifically, sample OPBI/MC-15 retained approximately 95% of its initial mass after 200 h in Fenton's reagent at 80 °C, representing a dramatic improvement over pristine OPBI. Single-cell tests delivered peak power densities of 592 and 887 mW cm −2 at 140 and 160 °C, respectively, with open-circuit voltages exceeding 0.97 V. This work demonstrates a synergistic strategy combining enhanced proton transport and oxidative stability for advanced HT-PEM applications.