Understanding Local Configurational Fluctuations in Vanadium Redox Flow Batteries using Atomistic Scale Simulations

Vanadium redox flow batteries (VRFB) have gained popularity as a flow battery technology due to its use of the same vanadium ions in different oxidation states as the redox couples. This design minimizes crossover contamination between the electrolytes, a common issue in other flow battery systems. However, to advance VRFB technology further, a more detailed understanding at the atomic level is required. Specifically, the mechanisms by which the ions in the electrolyte rearrange at the electrode interface in response to an applied potential still need to be fully understood. Furthermore, the ion adsorption mechanisms at the electrode surfaces, which are critical for the redox reactions, require more thorough investigation to enhance the system's overall efficiency.<br/><br/>Therefore, in this study, we use large-scale molecular dynamics simulations to better probe the dynamic evolution of local configurations of aqueous vanadium and sulfate species at the carbon electrode interface. In addition, we apply a constant potential method that enables us to probe the natural response of the electrolyte as a function of applied potential. Our results indicate that the local configurations vary with the vanadium charge state and the applied potential, with the most stable configuration being the outer-sphere adsorbed state. The modeling framework described in this study establishes a basis for systematically identifying and decoding fundamental reaction mechanisms that dictate the performance of VRFB.<br/><br/>This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344.