Ab Initio Study of Proton Transfer and Interfacial Properties in Phosphoric Acid‐Doped Polybenzimidazole

Quantum mechanics calculations and hybrid ab initio/empirical molecular dynamics simulations using the ONIOM scheme have been used to investigate proton transfer and interfacial properties in phosphoric acid (PA)‐doped polybenzimidazole. Quantum mechanics calculations indicate that hydrogen bonding between PA and benzimidazole (with PA as the hydrogen donor) is the major interaction between PA and polybenzimidazole at low PA‐doping levels. Comparing energy barriers for different proton transfer pathways indicates that proton transfer is prone to occur between the same molecules or between a molecule and its corresponding ion. The atom‐centered density matrix propagation approach coupled with ONIOM using density functional theory and universal force field calculations indicates that protonation of the “=N–” atom on the imidazole ring occurs when there are two or more PA molecules surrounding each imidazole ring. These conclusions agree with the experimental results in the literature.