Proton exchange membranes based on polybenzimidazoles and their composites

Abstract

Proton exchange membrane fuel cells (PEMFCs) have, by now, newlineemerged as one of the preferred fuel cells due to their several newlineadvantages including light weight, cost-effectiveness, high service life, newlineefficiency and non-corrosive nature. Phosphoric acid doped newlinepolybenzimidazole is considered as a superior alternative to newline newlineconventional high temperature proton exchange membranes (HT- newlinePEMs) being used in PEMFCs due to its excellent stability and high newline newlineconductivity. The objective of the present thesis is to develop newlinepolybenzimidazole membranes with high proton conductivity, good newlinemechanical properties (both in the doped and undoped conditions), and newlineexcellent oxidative and thermal stabilities. newlineInitially, the synthesis and characterization of a pyridine based low newlinemolecular weight polybenzimidazole powder (LMP) have been newlineexecuted [inherent viscosity (IV) = 0.52 dL/g]. The synthesized LMP newlinewas incorporated into poly (dimethylsiloxane) matrix (PDMS) to impart newlineproton conductivity (PBI powders were used as proton hopping fillers). newlineThe composite membrane containing 30 wt. % of LMP exhibited a newlineproton conductivity of 16 mS/cm at 100-120 °C with high oxidative newlinestability (weight loss after 120 h of Fenton s test was only 8.6%). newlineSubsequently, a high molecular weight polybenzimidazole (PPBI) was newlinesynthesized from pyridine dicarboxylic acid and hydrochloride salt of newlinediaminobenzidine. The synthesized PPBI was characterized by various newlinetechniques. Amine functionalized silica nanoparticles in different newlinedegrees of amine grafting (LAC-low amine content/HAC-high amine newlinecontent) were successfully incorporated into the PPBI to generate newlinenanocomposite membranes. newline