Protic ionic liquid and ionic melts prepared from methanesulfonic acid and 1H-1,2,4-triazole as high temperature PEMFC electrolytes

Protic ionic liquid and ionic melts were prepared from the combination of methanesulfonic acid (CH3SO3H) and 1H-1,2,4-triazole (C2H3N3) at various molar ratios. The thermal properties, crystal structure, acid-base interactions, ionic conductivity, proton conduction behavior and electrochemical stability of the system were studied. The equimolar composition, 1,2,4-triazolium methanesulfonate (C2H4N3+center dot CH3SO3- (1)), was a proton transfer salt with a melting point of around 134 degrees C. Single crystal and powder XRD data, as well as TGA results, revealed that the base-rich region was a mixture of 1 and 1H-1,2,4-triazole. Infrared analysis and single crystal data suggested that the C2H3N3-CH3SO3H system exists in a strongly hydrogen-bonded network. Systematic investigation of the ionic conductivity showed that the ionic conductivity reached local maxima at the compositions of [C2H3N3]/[CH3SO3H] = 10/90 and 80/20, respectively, while it exhibited a local minimum at the equimolar composition. The temperature dependence of the ionic conductivity was found to obey the Vogel-Fulcher-Tamman (VFT) equation. The fitting of the conductivity data to the VFT equation showed that the carrier ion concentration versus the mole fraction of 1H-1,2,4-triazole exhibited a volcano shape. In addition, the C2H3N3-CH3SO3H system showed adequate electrochemical stability under PEMFC conditions as measured by linear sweep voltammetry. The relatively high ionic conductivity, wide electrochemical window and good thermal stability demonstrated that the C2H3N3-CH3SO3H system is a suitable candidate for high temperature PEMFC electrolytes.