Synthesis and preparation of branched block polybenzimidazole membranes with high proton conductivity and single-cell performance for use in high temperature proton exchange membrane fuel cells

Abstract

The application of phosphoric acid (PA)-doped polybenzimidazoles (PBIs) in high-temperature proton exchange membrane fuel cells (HTPEMFCs) requires optimal proton conductivity and fuel cell performance. Recently, we found that branched PBIs could absorb more PA due to their large free volume, and block PBIs could yield obvious nanophase-separated structures, both of which were beneficial to proton transportation. Herein, by constructing a branched PBI core block with another derived PBI structure, a novel membrane with a star-shaped, branched block matrix was prepared for the first time. The dendritic polymer backbone with a phase separation path endows the membranes with high PA doping capacity and high-efficiency proton transmission. Noticeably, a high proton conductivity (0.15 S cm−1, 160 °C) and low activation energy (5.6 kJ mol−1) were obtained under anhydrous conditions, and the peak power density of the single-cell test was as high as 713 mW cm−2 at 160 °C. The results indicate that the combination of branching and a block structure is promising for actual use in HTPEMFCs.