5-(methacrylamido)tetrazole and vinyl triazole based copolymers as novel anhydrous proton conducting membranes

Abstract

Polymer electrolytes that have ability to conduct protons at high temperatures have become crucial as the membranes for proton exchange membrane fuel cells (PEMFC) in anhydrous systems. In this work, a novel copolymer based on 5-(methacrylamido)tetrazole (MTet) and vinyl triazole (VTri) was prepared by conventional free-radical copolymerization at several monomer feed ratios to attain poly(VTri-co-MTet) copolymers. The copolymer samples were doped with H₃PO₄ at several stoichiometric ratios to obtain proton conductive copolymer electrolytes. The obtained membranes were analyzed by FTIR, ¹H-NMR, Thermogravimetric Analysis (TGA), Differantial Scanning Calorimetry (DSC), Scanning Electron Microscopy (SEM), Cyclic Voltammetry (CV), and Impedance Spectroscopy. The compositions and molecular weights of copolymers were determined via ¹H-NMR analysis. TGA demonstrated that the copolymers are thermally stable up to approximately 220 °C. DSC results illustrated both the homogeneity of the materials by the appearance of a single T_g and the plasticizing effect of the dopant. SEM analysis provided further evidence for the homogeneity of the membranes. CV results demonstrated that the stability window of P(VTri-co-MTet) is 3 V. The copolymer electrolytes, P(VTri-co-MTet)2:1 X = 2, P(VTri-co-MTet)1:1 X = 2, and P(VTri-co-MTet)1:2 X = 2 showed maximum proton conductivities of 0.012 Scm⁻¹, 0.014 Scm⁻¹ and 0.016 Scm⁻¹, respectively, at 150 °C and anhydrous conditions.