Gaining Insights on Interfacial Dynamics of Methyl Viologen Based Aqueous Organic Redox Flow Battery through a Kinetic Monte Carlo Approach

Aqueous organic redox flow batteries (AORFB) have become the promising pitch in large scale energy storage facilities, which offer fast electrochemistry kinetics, and relatively low system cost [1]. Nonetheless, finding the perfect redox couples in AORFB cells among all the possible candidates remains challenging, while the electrochemistry mechanisms behind the cell operation remain generally poorly understood. Here we present a novel mesoscale kinetic Monte Carlo (kMC) algorithm combined with a dynamic electric double layer (EDL) approach allowing us to investigate in depth the electrochemical kinetics in a methyl viologen (MV) based AORFB cell. The resulting three-dimensions computational model, adapted from our previous works in different applications [2,3,4,5,6], simulates the stochastic processes happening at the electrode/anolyte interface from a molecular level viewpoint by assigning different rates to different events. In this study, three key events have been included in the model: molecular motion, electrochemical reaction, and dimerization. Both diffusion and electromigration are considered as the driving forces for molecular motion, while the electromigration effects are calculated through the EDL approach. The electrochemistry reaction rate considers the reorganization energy, which varies as a function of the electronic tunneling distance between the electrode and the anolyte. The dimerization event allows capturing MV's capacity degradation in agreement with experimental knowledge. The model has been used to simulate the galvanostatic discharging process with different input current densities and electrolyte concentrations. Along the simulation time, the model simulates the system's electrochemical response while providing insights on the dynamic EDL structure evolution and potential dynamics. The calculated observables are in good agreement with empirical knowledge advancing the understanding of these complex electrochemical interfaces' behavior. This mesoscale kMC model paves the way towards a tool able to scale up computational screening results arising from Density Functional Theory calculations into kinetics simulation of AORFB electrochemical interfaces, as being done by us in the context of the EU-funded project "SONAR" [7]. References [1] Noack, J., Roznyatovskaya, N., Herr, T. and Fischer, P. (2015), The Chemistry of Redox‐Flow Batteries. Angew. Chem. Int. Ed., 54: 9776-9809. [2] Thangavel, V., Guerrero, O. X., Quiroga, M., Mikala, A. M., Rucci, A., & Franco, A. A. (2020). A three- dimensional kinetic Monte Carlo model for simulating the carbon/sulfur mesostructural evolutions of discharging lithium sulfur batteries. Energy Storage Materials, 24, 472-485. [3] Shukla, G., & Franco, A. A. (2018). Handling complexity of semisolid redox flow battery operation principles through mechanistic simulations. The Journal of Physical Chemistry C, 122(42), 23867-23877. [4] Shukla, G., del Olmo Diaz, D., Thangavel, V., & Franco, A. A. (2017). Self-organization of electroactive suspensions in discharging slurry batteries: a mesoscale modeling investigation. ACS applied materials & interfaces, 9(21), 17882-17889. [5] Yin, Y., Zhao, R., Deng, Y., & Franco, A. A. (2017). Compactness of the Lithium Peroxide Thin Film Formed in Li–O2 Batteries and Its Link to the Charge Transport Mechanism: Insights from Stochastic Simulations. The journal of physical chemistry letters, 8(3), 599-604. [6] Quiroga, M. A., & Franco, A. A. (2015). A multi-paradigm computational model of materials electrochemical reactivity for energy conversion and storage. Journal of The Electrochemical Society, 162(7), E73. [7] https://www.sonar-redox.eu/en/About.html Figure 1