Properties of Polymer Electrolyte Membranes Based on Poly(Aryl Ether Benzimidazole) and Sulphonated Poly(Aryl Ether Benzimidazole) for High Temperature PEMFCs

Membranes based on poly[2,2′‐(p‐oxydiphenylene)‐5,5′‐bibenzimidazole] (OPBI) and their sulphonated derivatives (SOPBI) were prepared and first investigated for high temperature proton exchange membrane fuel cells. OPBI and SOPBI membranes with good chemical stability were prepared by casting from their dimethyl sulphoxide (DMSO) solution and then impregnated in phosphoric acid baths to obtain H 3 PO 4 (PA)‐doped membranes. The properties of PA‐doped OPBI membranes, including phosphoric acid uptake, swelling ratio, mechanical properties and thermal properties, were fully investigated and compared with PA‐doped SOPBI membranes. The fuel cell performances of PA‐doped OPBI and SOPBI membranes at different temperatures were first evaluated. When doped in different concentrations of H 3 PO 4 solution, OPBI membranes adsorb more acid than SOPBI membranes. SOPBI membranes exhibit obviously lower swelling ratio in thickness direction than that of OPBI membranes. With an acid uptake of ∼110 wt.‐%, corresponding doping level around 5, PA‐doped OPBI and SOPBI membranes keep reasonably high tensile strength. PA‐doped OPBI membranes exhibit peak power density of 0.78 W cm –2 at 170 °C and 0.25 MPa. With the same acid uptake, PA‐doped SOPBI membranes displayed similar fuel cell performance to that of PA‐doped OPBI membranes.