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

摘要

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 ℃ 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.