Chitosan modified by nitrogen-containing heterocycle and its excellent performance for anhydrous proton conduction

Abstract

A chitosan-based polymer was successfully synthesized by condensation reaction with 1H-tetrazole-1-acetic acid in order to reduce the alkalinity of chitosan and enhance the nitrogen site density as well as the flexibility. Phosphoric acid was introduced into the polymer system by immersing the membrane into acidic solution with various concentrations to improve the proton conductivity. The performances of the modified material were investigated in detail as a function of the immersing phosphoric acid concentration. As observed, the tetrazole-grafted chitosan polymer shows a proton conductivity of 2.08 × 10⁻⁴ S cm⁻¹ at 150 °C, ten times higher than that of chitosan. When doped with phosphoric acid, a high conductivity of 2.3 × 10⁻² S cm⁻¹ was obtained at 150 °C, which was three times higher than the acid-doped chitosan. The tetrazole-grafted chitosan also shows better performance than chitosan in terms of mechanical strength and oxidative stability. All these results indicate that the tetrazole-grafted chitosan is an excellent potential anhydrous proton conductor.