Achieving high power density of 859.5 mW cm−2: Self-cross-linking polymer membrane based on rigid fluorenone structure

Plasticization of phosphoric acid (PA) leads to deterioration of the mechanical properties of polybenzimidazole membranes. It has been widely accepted that cross-linking is an effective method to improve mechanical properties of membranes. However, cross-linked membranes generally exhibit decreased proton conductivity and poor fuel cell performance. In this work, a self-cross-linking copolymer based on rigid fluorenone-modified polybenzimidazole (FPBI) are designed and synthesized as high-temperature proton exchange membranes for the first time. The cross-linked FPBI membranes are prepared through solvent casting and the cross-linking degrees of the membranes can be controlled by adjusting membrane preparation temperature and evaporation speed of the solvent. The membranes exhibit excellent mechanical properties and high proton conductivities. The membrane with FPBI-80 °C exhibits high oxidation resistance (>80 wt%), PA retention property (>90 wt%), tensile strength (12.08 MPa), and elongation at break (212.7%). The single cell based on FPBI-80 °C exhibits a high open-circuit voltage (1.01 V) and excellent peak power density of 859.5 mW cm−2 at 160 °C in an anhydrous environment. Herein, the FPBI membrane is expected to be applied in high-temperature fuel cells.