Phosphoric acid (PA)-doped polybenzimidazole (PBI) membranes hold significant promise for high-temperature proton exchange membrane fuel cells (HT-PEMFCs), yet PA leaching at elevated temperatures due to weak PBI-PA interactions restricts their long-term performance. To address this limitation, we introduced cationized lignin into the PBI matrix. Novel cationizing agent with two epoxy groups and two quaternary ammonium groups (DEpDQAS) were synthesized first, and subsequently grafted onto the lignin, yielding highly quaternized lignin. By carefully controlling the cationization degree and the PBI-to-cationic lignin ratio, we enhanced ion-pair interactions, leading to superior PA retention within the membrane. The resulting composite membranes exhibited significantly improved proton conductivity and structural durability compared to pristine PBI. Overall, the integration of bio-derived lignin offers a sustainable and environmentally friendly approach for the development of high-performance HT-PEMFC membranes.
