Composite membranes consisting of acidic carboxyl-containing polyimide and basic polybenzimidazole for high-temperature proton exchange membrane fuel cells

Abstract

A novel acid-base composite membrane consisting of acidic carboxyl-containing polyimide (PI-COOH) and basic polybenzimidazole (OPBI) was fabricated and employed as a high-temperature proton exchange membrane (HT-PEM). PI-COOH was used to prepare HT-PEMs for the first time. The PBI-based acid-base composite membranes and ordinary composite membranes were investigated to elucidate the correlation between the polymer structure and membrane properties, especially in situations where phosphoric acid (PA) is used. The results show that OPBI-xPI-COOH composite membranes (x represents the weight percentage of PI-COOH in the entire membrane) deliver high proton conductivities and superior PA retention due to the continuous hydrogen bond network between OPBI and PI-COOH. The OPBI-50PI-COOH composite membrane revealed a proton conductivity of 89 mS cm⁻¹ under low PA uptake (109%). Compared to the linear OPBI and OPBI-40PI composite membrane, a single cell with a low PA-doped OPBI-50PI-COOH composite membrane presented superior durability and power density (463 mW cm⁻²) at 160 °C and 0% relative humidity. In a short-term durability test of 369 h, the voltage attenuation rate was only 119 μV h⁻¹. These outstanding outcomes indicate that the obtained acid-base composite membranes can be considered as capable candidates for HT-PEMs with enhanced performance.