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

Abstract

The boron phosphate-poly(2,5-benzimidazole) (or BPO4–ABPBI) nanocomposite proton exchange membranes were prepared by preblending BPO4 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 BPO4 nanoparticles; and a maximum proton conductivity of 27.3 mS cm−1 was observed in the phosphoric acid doped nanocomposite membrane consisting of 25% BPO4 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 BPO4 nanoparticles based on density functional theory calculations. In addition, the blending of BPO4 nanoparticles significantly decreases the methanol vapor permeability through the membrane by about two-fold.