Polyethyleneimine-filled sepiolite nanorods-embedded poly(2,5-benzimidazole) composite membranes for wide-temperature PEMFCs

Proton-exchange membrane fuel cells (PEMFCs) that operate from room temperature to high temperatures (e.g., 200 °C) are desired for fuel cells used in vehicles and combined heat and power systems. In this work, polyethyleneimine-filled sepiolite nanorods (PEI@SNR)-embedded poly(2,5-benzimidazole) composites (ABPBI/PEI@SNR) were synthesized in-situ to enhance their proton conductivity and minimize phosphoric acid (PA) leaching. They were then applied in PEMFCs between room temperature and 200 °C. The physicochemical and electrochemical properties of the composite membranes were characterized. The composite membranes showed enhanced thermal, oxidative, and dimensional stability and achieved proton conductivities above 0.01 S/cm from 40 to 200 °C at a relative humidity of 0–100%. This performance was attributed to abundant hydrogen bonds between PA, ABPBI, and PEI, and the strong retention of bound water within sepiolite nanorods (SNRs). The maximum power density of the cell based on the PA-doped ABPBI/5PEI@SNR composite membrane reached 0.16 W/cm² at 80 °C and 0.27 W/cm² at 180 °C and an anhydrous environment, which were respectively 2.2 and 1.5 times higher than those of the PA-doped ABPBI membrane. The cell performance was much better than previously reported zeolite-embedded polybenzimidazole membrane-based PEMFCs, indicating that the composite membranes have good application prospects in PEMFCs operating over a wide temperature range.