Dimethylimidazolium-Functionalized Polybenzimidazole and Its Organic–Inorganic Hybrid Membranes for Anion Exchange Membrane Fuel Cells

Abstract

A quaternized polybenzimidazole (PBI) membrane was synthesized by grafting a dimethylimidazolium end-capped side chain onto PBI. The organic–inorganic hybrid membrane of the quaternized PBI was prepared via a silane-induced crosslinking process with triethoxysilylpropyl dimethylimidazolium chloride. The chemical structure and membrane morphology were characterized using NMR, FTIR, TGA, SEM, EDX, AFM, SAXS, and XPS techniques. Compared with the pristine membrane of dimethylimidazolium-functionalized PBI, its hybrid membrane exhibited a lower swelling ratio, higher mechanical strength, and better oxidative stability. However, the morphology of hydrophilic/hydrophobic phase separation, which facilitates the ion transport along hydrophilic channels, only successfully developed in the pristine membrane. As a result, the hydroxide conductivity of the pristine membrane (5.02 × 10−2 S cm−1 at 80 °C) was measured higher than that of the hybrid membrane (2.22 × 10−2 S cm−1 at 80 °C). The hydroxide conductivity and tensile results suggested that both membranes had good alkaline stability in 2M KOH solution at 80 °C. Furthermore, the maximum power densities of the pristine and hybrid membranes of dimethylimidazolium-functionalized PBI reached 241 mW cm−2 and 152 mW cm−2 at 60 °C, respectively. The fuel cell performance result demonstrates that these two membranes are promising as AEMs for fuel cell applications.