Gaining Insight into the Electrochemical Interface Dynamics in an Organic Redox Flow Battery with a Kinetic Monte Carlo Approach

Abstract

The available solution is developing an efficient, economical, and environmentally friendly large-scale energy storage device to balance the production and demand of electricity. The redox flow battery (RFB) system is a promising candidate among all the energy storage devices due to its relatively low cost, high energy efficiency, and feasibility for large-scale energy storage applications.To date, vanadium-based redox flow batteries (VRFB) are among the most reliable RFB technologies due to their limited cross-contamination effect and relatively large power output. Moreover, the electrolyte of a VRFB shows limited aging, which is the main reason for its high capacity retention rate. [1,2] However, compared with the E.U. cost target (150 € kW h −1 ), [3] a VRFB system remains relatively expensive (≈400 € kW h −1 for 2 kW-class facilities) [4,5] due to the cost of the ion exchange membrane and raw materials. Meanwhile, vanadium mining and production lead to soil pollution and a toxic impact on plants, animals, and humans around the mining sites. [6] Therefore, organic redox flow batteries (ORFBs) have attracted much attention due to the significantly faster redox kinetics, the ability to tune electrochemical properties through organic synthesis, and the low Finding low-cost and nontoxic redox couples for organic redox flow batteries is challenging due to unrevealed reaction mechanisms and side reactions. In this study, a 3D kinetic Monte Carlo model to study the electrode-anolyte interface of a methyl viologen-based organic redox flow battery is presented. This model captures various electrode processes, such as ionic displacement and degradation of active materials. The workflow consists of input parameters obtained from density functional theory calculations, a kinetic Monte Carlo algorithm to simulate the discharging process, and an electric double layer model to account for the electric field distribution near the electrode surface. Galvanostatic discharge is simulated at different anolyte concentrations and input current densities, which demonstrate that the model captured the formation of the electrical double layer due to ionic transport. The simulated electrochemical kinetics (potential, charge density) are found to be in agreement with the Nernst equation and the obtained EDL structure corresponded with published molecular dynamics results. The model's flexibility allows further applications of simulating the behavior of different redox couples and makes it possible to consider other molecular-scale phenomena. This study paves the way for computational screening of active species by assessing their potential kinetics in electrochemical environments.

Static theoretical investigations of organic redox active materials for redox flow batteries

“…The different degradation mechanisms need an assumed degradation reaction and system-specific quantum chemical modeling. The systematic theoretical research of the stability of redox-active molecules is therefore a specific and complex problem [30,56]. In screening approaches, for example, the redox potentials of many redox active molecules are calculated, and degradation is usually not taken into account.…”