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; 9010 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 degrees 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 degrees 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.