Phosphoric acid-doped poly(1-vinyl-1,2,4-triazole) as water-free proton conducting polymer electrolytes

The development of anhydrous proton conducting membrane is important for the operation of polymer electrolyte membrane fuel cell (PEMFC) at intermediate temperature (100–200 °C). In the present work, poly(1-vinyl-1,2,4-triazole), PVTri was produced by free radical polymerization of 1-vinyl-1,2,4-triazole with a high yield. The molecular weight of the homopolymer was measured via gel permeation chromatography (GPC) and Mw was found to be 104,216 g/mol. The structure of the homopolymer was proved by solid state 13C CP-MAS NMR spectroscopy. The polymer was doped with phosphoric acid at various molar ratios x = 1 and x = 2. The proton transfer from H3PO4 to the triazole rings was proved with Fourier-transform infrared spectroscopy (FT-IR). Thermogravimetry (TG) analysis showed that the samples are thermally stable up to approximately 250 °C. Differential scanning calorimetry (DSC) results illustrated the homogeneity of the materials as well as the plasticizing effect of the dopant. The electrochemical stability of the materials was studied by cyclic voltammetry (CV). The proton conductivity of these materials increased with dopant concentration and the temperature. In the anhydrous state, the proton conductivity of PVTri 1 H3PO4 is 5 × 10− 3 S/cm at 150 °C and the conductivity of PVTri 2 H3PO4 was 4 × 10− 3 S/cm at 140 °C.