Synthesis and Properties of Segmented Block Copolymers of Functionalised Polybenzimidazoles for High-Temperature PEM Fuel Cells

A series of novel segmented block copolymers of sulphonated polybenzimidazole (PBI) (s‐PBI) and p‐PBI were prepared with various polymer ratios (10–90 mol% s‐PBI; 90‐10 mol% p‐PBI). A two‐step synthesis of oligomeric species, followed by combination and further polymerisation was used via the polyphosphoric acid (PPA) process. The membranes showed improved high‐temperature proton conductivities and fuel cell performance over previous literature reports, with moderate incorporation of s‐PBI into the copolymer showing the best results. The non‐humidified fuel cell performance was extensively studied with various fuels and oxidants and showed excellent properties. Block copolymers that incorporated 40, 50 or 60 mol% s‐PBI and the corresponding 60, 50 or 40 mol% p‐PBI, at 0.2 A cm–2 and 160 °C, had hydrogen–air performances of 0.661–0.666 V, depending on composition. The performance was improved using hydrogen–oxygen, with voltages between 0.734 and 0.742 V at 0.2 A cm–2 and 160 °C. Fuel cells operating on a reformed hydrocarbon gas showed decreased performance (0.622–0.627 V, same conditions), especially at lower temperatures, but was significantly improved over previous literature reports of sulphonated PBI membranes operating at high temperatures.