Molecular Insights into Binary Ionic Melts of Protic Ionic Liquid 1,2,4-Triazolium Methanesulfonate and Methanesulfonic Acid Electrolytes

Binary ionic melts formed by a protic ionic liquid (PIL) 1,2,4-triazolium methanesulfonate ([TAZ][MS]) dissolved in methanesulfonic acid are studied as non-stoichiometric electrolytes. The composition-driven structure-property relationship of methanesulfonic acid is explored at varying molar fraction ratios from 0/100 to 10/90, 20/80, and 30/70 by the addition of 1,2,4-triazolium methanesulfonate [TAZ][MS] IL. To unveil molecular characteristics of these mixtures of [TAZ][MS] PIL and CH₃SO₃H, we performed classical molecular dynamics simulations at varying temperatures from 293 to 303, 363, and 423 K. Ion-pair interactions and ion-solvent interactions are captured through various atom-atom radial distribution functions, and hydrogen bonding is presented through N-H hydrogen atom interactions with the [MS]^- anion or CH₃SO₃H oxygen atoms. Apart from the temperature, the PIL ratio itself plays a critical role in hydrogen bonding interactions, and spatial density distribution maps show strengthening of ion-pair interactions with an increase in PIL concentration. The mobility of ions and CH₃SO₃H is also explored through mean square displacement plots and by calculating the diffusion coefficient. The diffusion coefficient is used to calculate Nernst-Einstein conductivity, which shows an excellent match with experimental conductivity at 363 and 423 K.