Molecular Dynamics Simulation of the Electrochemical Cell Design for All- vanadium Redox Flow Battery

Abstract

Being the most potential battery candidate for the electrical grids connections due to having promising electrochemical energy storing abilities, vanadium redox flow battery (VRFB) is widely recognized state-of-the-art technology in renewable energy sectors. Despite its uniqueness of utilizing "all-vanadium" redox couples as the most prospective electrolyte materials, and their conspicuous technological functionalizations, the research works concentrated into its internal operational mechanisms of the cell at both ideal & different state-of-charges are still in the primitive stage. This MD simulation based theoretical insights aiming at revealing benchmark quantitative information on the interfacial micro structures around its Nafion-117 type proton exchange membrane, the intense hydration affinities of its adjacent state bare Vn+ ions, and the closed proximity around the H2O, H3O+, & Nafion-SO3-, etc. at nanometer scale would be a stepping-stone to its technological advancement. The general results presented here illuminate that the VRFB-electrolyte hosting H2O molecules and protons in Hydronium (H3O+), Eigen (H5O2+), & Zundel (H9O3+) states are distributed in a pattern identical to that in a purely bulk water system, and are dynamically used up for exhibiting facile proton conduction. Besides this, the significant departures of the SO3- units of the Nafion-117 at water content (l) = 22 predicted herein confirms its experimentally observed feature of easy accommodating H2O, H3O+, & Vn+ in between them; elucidating the reasons behind its atypical proton conductivity & ionic mobility rates under wet conditions. The MD trajectories based radial distribution function (RDF) predicted Vn+- OH2 radial distances validate the extreme hydration affinities of the bare adjacent Vn+ ions plus their stabilizing propensities with free H2O molecules as established earlier by the DFT based quantum mechanical method.