Enhancing the high-temperature proton conductivity of phosphoric acid doped poly(2,5-benzimidazole) by preblending boron phosphate nanoparticles to the raw materials

The boron phosphate-poly(2,5-benzimidazole) (or BPO 4 –ABPBI) nanocomposite proton exchange membranes were prepared by preblending BPO 4 nanoparticles to the 3,4-diaminobenzoic acid solution before its polycondensation . The phosphoric acid doped nanocomposite membrane possesses enhanced proton conductivity compared to the phosphoric acid doped pristine ABPBI membrane without BPO 4 nanoparticles; and a maximum proton conductivity of 27.3 mS cm −1 was observed in the phosphoric acid doped nanocomposite membrane consisting of 25% BPO 4 nanoparticles at 180 °C under anhydrous condition. The enhancement of proton conductivity is attributed to the dangling hydroxyl or geminal hydroxyl groups of the excess phosphoric acid molecules on surface of the BPO 4 nanoparticles based on density functional theory calculations. In addition, the blending of BPO 4 nanoparticles significantly decreases the methanol vapor permeability through the membrane by about two-fold.