Arylether-type polybenzimidazoles bearing benzimidazolyl pendants for high-temperature proton exchange membrane fuel cells

Abstract

Phosphoric acid-doped polybenzimidazole membranes offer great potential for high-temperature proton exchange membrane applications due to their high proton conductivity at high-temperature and low-humidity conditions. However, it remains a major challenge in fabricating high-performance membranes with both high proton conductivity and good mechanical strength. Here, a series of polybenzimidazoles with increased imidazole groups are obtained by incorporating some benzimidazole groups onto an arylether-type polybenzimidazole backbone via a simple and efficient N-substituted reaction without catalyst. This arylether-type polybenzimidazole is verified to exhibit good solubility under extremely high molecular weight, and it provides the possibility for fabricating the high mechanical strength membranes at high phosphoric acid doping levels. It is of interest to find that the introduction of additional bulky benzimidazole moieties even enhance the mechanical strength of the membranes, and at the same time, significantly improve their acid doping levels, acid doping rate and proton conductivity. Importantly, the acid-doped grafted membranes show superior dimensional-mechanical stability even at high acid loading. With an acid doping level of 22.1, the grafted membrane displays a high conductivity of 212 mS cm−1 at 200 °C without humidification. A H2/O2 fuel cell based on this membrane has a peak power density of 443 mW cm−2 at 160 °C.