(192ax) First-Principles Study of Atomistic Mechanisms in All-Vanadium Redox Flow Batteries

All-vanadium redox flow batteries (RFBs) is a promising large-scale grid energy storage which offers a number of advantages over their solid-state counterparts including the decoupling of power and energy, rapid response times, reversibility and long cycling lifespan. The operation of all-vanadium RFB is based on the electrochemical reactions of the VO^2+/VO₂⁺ redox couple in the catholyte and the V²⁺/V³⁺ in the anolyte. Two critical parameters that dictate the overall efficiency of a RFB are energy density and power density. However, atomistic mechanisms of electrochemical reactions in the electrolyte and at the electrolyte/electrode interfaces responsible for enhanced energy and power density, respectively, are still poorly understood.

In this study we provide crucial insights into the mechanisms of vanadium self-discharge reactions in the electrolyte and interactions of graphite electrode surfaces with vanadium ions utilizing static DFT and Car-Parrinello molecular dynamics (CPMD) based metadynamics simulations.¹ Specifically, we find that vanadic acid formed in solution should play an important role in polymerization and self-discharge reactions, and we provide the energetics for various reaction pathways. For the electrode reactions, our results suggest that the edge surface is characterized by the formation of ketonic C=O functional groups due to complete water dissociation into H/O/H configuration with surface O atoms serving as active sites for adsorption of V²⁺/V³⁺ species.² The formation of V-O bonds at the surface should significantly improve the kinetics of electron transfer at the edge sites that is not the case for basal surface, in agreement with experimentally hypothesized mechanism.

1 Jiang Z., Klyukin K. and Alexandrov V. Structure, Hydrolysis and Diffusion of Aqueous Vanadium Ions from Car-Parrinello Molecular Dynamics. J. Chem. Phys. 2016, 145, 114303-114311

2 Jiang Z., Klyukin K. and Alexandrov V. First-Principles Study of Adsorption-Desorption Kinetics of Aqueous V²⁺/V³⁺ Redox Species on Graphite in a Vanadium Redox Flow Battery. submitted.