Building block candidates for the design of proton exchange membranes: Maleimide and its homologues

Density functional theory (DFT) calculations are applied to the study of proton transport in maleimide and its homologues, succinimide and phthalimide. The calculations reproduce correctly their structural characteristics and reveal the hydrogen bonding and proton hopping properties. Specifically, the calculations show that the potential barrier for proton transfer between two maleimide molecules is about 30.60 kcal mol−1 mediated by one or two water molecules with correction of solvation effect by water, and will decrease to about 13.22 kcal mol−1 if ethylphosphonic acid molecule is used as mediator with correction of solvation effect by phosphoric acid. In addition, the calculations also show that succinimide and phthalimide possess similar characteristics compared to maleimide. Finally, it is concluded that maleimide and its homologues are building block candidates for the design of high-temperature proton exchange membranes.