A molecular insight into formation of deep eutectic solvents and their application for the enhancement of proton transportation via graphene oxide-based proton exchange membranes

Abstract

The new electrolytes (ethylene glycol (EGL)- and sodium halide-based deep eutectic solvents (DESs)) could enable us to solve the chemical instability and proton transportation problems of proton exchange membrane (PEM) under harsh operating conditions, which is related to the hydroperoxyl or hydroxyl radical’s formations that will attack on the backbones and side chains of PEM. In this regard, the intermolecular interaction of EGL- and sodium chloride-based DES and then its application for the transportation of proton in graphene oxide (GO) based membrane was studied via the classical all-atom molecular dynamics (MD) simulations. The MD results revealed that the decrease in radial distribution function peak height and number of hydrogen bonding per molecule between EGL, and the formation of new intermolecular interaction between EGL/sodium chloride after the addition of DES components at 298 and 350 K, respectively. Next, the modelling and simulations of the GO and hydronium ion were investigated to mimic the transportation process of hydronium ion via PEM in the absence and presence of EGL- and sodium chloride-based DES. In the absence of DES, the results implied that the hydronium ion diffusion coefficient and the diffusion coefficients of water molecules are similar, because vehicular diffusion mechanism needs synchronized diffusion of both species (water and hydronium ion) at hydration level ($\lambda$) 3. Moreover, the transportation of proton increased monotonically as an increase of $\lambda$ at 298 and 350 K, respectively. Next, in the presence of EGL- and sodium chloride-based DES electrolyte in GO-based proton exchange membrane yielded improved mobility of hydronium ions at higher temperature (350 K), which could mean that DES could be a promising alternative as an electrolyte for PEM.