A molecular investigation of the nanostructure and dynamics of phosphoric-triflic acid blends of hydrated ABPBI [poly(2,5-benzimidazole)] polymer electrolyte membranes

Abstract

Poly(2,5-benzimidazole) membranes (ABPBI) doped with phosphoric acid (PA) are known to serve as promising electrolytes in fuel cells. The addition of triflic acid, which exist in its dissociated form (TFA), is known to enhance the efficiency of PA-doped ABPBI membranes. In the present work, we employ classical molecular dynamic simulations to characterize the structure and dynamics of ABPBI + PA, ABPBI + TFA and ABPBI + PA + TFA blends with varying levels of hydration. The structural properties seen from the radial distribution functions (RDFs) show that the distance between two adjacent imidazole units on the polymer chain remain unaffected by hydration and the type of blend. The end-to-end polymer chain distance and radius of gyration are also unaffected by hydration and the type of blend, illustrating that the stability of polymer membranes under various hydrated acidic environments remains unaffected. The number of PA, TFA and water molecules in the cluster around the polymer membrane (skewed and extended form) is found to depend significantly on the extent of hydration. The lowest water mobility was obtained from the ABPBI + PA + TFA blend, which suggests that this blend could be the most effective in reducing acid leaching from the membrane matrix.