A molecular dynamics study on polybenzimidazole based proton exchange membrane with dual proton conductors

Organophosphorus acid (OPA) and phosphoric acid (PA) acting as dual proton conductors co-doped into proton exchange membrane is an effective solution to simultaneously improve the proton conductivity and inhibit the leaching of PA for high temperature proton exchange membrane fuel cells (HT-PEMFCs). However, the interactions of the dual proton conductors with polymers are still unrevealed. Here we combined density functional theory (DFT) calculation with molecular dynamic (MD) simulations to investigate the interactions between amino tris (methylene phosphonic acid) (ATMP, a kind of OPA)/PA and polybenzimidazoles with different kinds of electron withdrawing groups. The study reveals strong electron-withdrawing groups could form more abundant hydrogen bonds networks, and the interactions of ATMP and PA with polybenzimidazoles lead to more free PA molecules, which both benefit the proton conductivity. Meanwhile, the addition of ATMP could reduce self-diffusion of PA, which could improve the PA retention capacity. This work provides insights for the design of high temperature proton exchange membranes.