Preparation and investigation of block polybenzimidazole membranes with high battery performance and low phosphoric acid doping for use in high-temperature fuel cells

Although phosphoric acid-doped polybenzimidazoles (PA-doped PBIs) are widely accepted in high-temperature proton exchange membrane fuel cells, further improvement is desirable to obtain optimal fuel cell performance. Block copolymers applied as low-temperature proton exchange membranes have been recently shown to exhibit high proton conductivity and fuel cell properties. However, few block copolymers have been reported as high-temperature proton exchange membranes. In this work, a series of segmented block PA-doped PBIs are synthesized with various molar ratios and similar molecular weights. The block copolymer membranes show obvious nanophase-separated structures due to the combination of rigid and flexible segments in the copolymer. A high proton conductivity of the block membrane is obtained at lower phosphoric acid doping levels (0.1 S cm−1 at 180 °C). The fuel cell performance of the block membranes exhibits a maximum power density of 360 mW/cm2 at 160 °C, which is higher than that of pristine poly[2,2′-(p-oxydiphenylene)-5,5′-benzimidazole] (OPBI) membranes (268 mw/cm2). The results suggest that block PBI doped with phosphoric acid can potentially be applied as a high-temperature proton exchange membrane.