Methanol permeation and proton conductivity of acid-doped poly(N-ethylbenzimidazole) and poly(N-methylbenzimidazole)

In the present work, poly(N-methylbenzimidazole) (PNMBI) and poly(N-ethylbenzimidazole) (PNEBI) were synthesized by methylation and ethylation of polybenzimidazole (PBI). Methanol permeability of PNMBI, PNEBI, and PBI was studied. Effects of methanol concentration and temperature on methanol permeability of PNMBI, PNEBI, and PBI membranes are discussed. The results show that PBI, PNMBI and PNEBI membranes are good methanol barrier. Methanol permeability in PBI, PNMBI and PNEBI membranes decrease with increasing methanol concentration. Temperature dependence of methanol permeability of PBI membrane can be fitted by Arrhenius equation. Proton conducting materials based on N-substituted PBI were prepared by successive immersion of the membranes in phosphoric acid solution. Interaction between PNMBI and phosphoric acid was studied by FTIR. It is indicated that the interaction in PNMBI/xH3PO4 and PBI/xH3PO4 is mainly due to the protonation. Proton conductivity of phosphoric acid-doped PNMBI and PBI was investigated by impedance measurements. Proton conductivity of acid-doped PNMBI increases with the increasing doping level and temperature. Proton conductivity of phosphoric acid-doped PNMBI and PBI is governed by a hopping mechanism rather than a mechanism mediated by the segmental motions in the polymer.