New Multiblock Copolymers Containing Quaternary Ammonium Groups with Ultramicroporous Structure for High-Temperature Proton Exchange Membrane Fuel Cells

Polybenzimidazole (PBI) exhibits considerable advantages as a leading membrane material for high-temperature proton exchange membrane fuel cells (HT-PEMFCs). However, their harsh synthesis conditions and high processing costs have greatly restricted the large-scale commercialization of HT-PEMFCs. Therefore, developing high-performance and durable membrane materials as alternatives to PBI has been recognized as the key technical challenge for the advancement of HT-PEMFC technology. In this study, a series of novel multiblock copolymers QPSBI-b-xTMA, consisting of acidophobic pentafluorophenyl, acidophilic quaternary ammonium groups, and high free-volume spirobisindane, were synthesized by a straightforward polymerization process involving two kinds of low-molecular-weight oligomers with different structures. The resulting multiblock membranes QPSBI-b-xTMA demonstrate well-defined microporous properties, and the PA-doped membranes exhibit a microphase separation structure, which effectively facilitates proton conduction (75.45 mS cm^–1@200 °C). The HT-PEMFCs based on the QPSBI-b-xTMA/PA membrane can operate efficiently within the temperature range of 160–220 °C, achieving a high peak power density of 0.84 W cm^–2 without external pressure and humidity. Notably, owing to the siphoning effect of the micropores and the strong quaternary ammonium-biphosphate ion pairs, the fuel cell exhibits a stable performance at a high current density of 0.5 A cm^–2 at 160 °C, with a minimal voltage degradation rate of merely 4.7 μV h^–1. Thus, the newly developed QPSBI-b-xTMA/PA materials present a promising avenue for HT-PEMFC applications.