Proton-exchange membranes based on phosphoric acid-doped polybenzimidazole (PBI) were fabricated and characterized for air-breathing microbial fuel cell (MFC) applications. Molecular dynamics (MD) simulation approaches were also employed to get an in-depth understanding of structure-property relationship of MFC membranes. Addition of 500 mol% phosphoric acid to PBI membrane enhanced its water uptake in comparison with neat PBI due to strong phosphoric acid-water interactions as revealed by MD simulations. Acid-doped PBI membranes resulted in reduced oxygen permeability (0.36 barrers) relative to Nafion (1.78 barrers). Moreover, MFC membranes based on acid-doped PBI produced higher open-circuit voltage and maximum power density of 471 mV and 74.2 mW cm(-2), respectively, as compared to corresponding open circuit voltage of 396 mV and maximum power density of 48.6 mW cm(-2) for Nafion membranes. Superior electrochemical properties of acid-doped PBI over Nafion were ascribed to MD predicted considerably lower diffusion coefficients of ions and oxygen molecule in acid-doped PBI than in Nafion. Owing to the attained desirable characteristics, fabricated phosphoric-acid doped PBI membranes could act as promising candidate membranes for MFC usages.