(688b) Oxidative Depolymerization of Lignin to Aqueous Electrolytes for Redox Flow Batteries

Interest has constantly been present in the valorization of lignin, an underutilized renewable resource with high aromaticity. Nevertheless, in today's society, with a heightened emphasis on resource sustainability, it is gaining more significance. In this study, a novel aqueous electrolyte is developed using lignin from elephant grass (EGL) and used as redox species in a redox flow battery (RFB) system. The EGL is extracted from the plant material of Miscanthus under alkaline conditions via a multi-step process. Oxidative depolymerization is employed to alter the original lignin in order to design electrochemical functionalities that are appropriate for use in the RFB application. Response surface methodology based on a face-centered central composite design is used to identify the optimal conditions for maximizing the lignin monomer yield. The effects of four independent parametric factors, i.e., temperature (160–220 °C), pressure (5–15 bar O₂), residence time (30–90 min), and lignin concentration (50–150 g/L), on the depolymerization process are investigated. The optimal operating conditions for the monomer yield were identified, with a predicted yield of 5.3 wt%. Electrochemical characterization of the oxidatively depolymerized lignin (OEGL) displayed favorable electrochemical reversibility and stability for 200 cycles at a constant current of 1 mA/cm². Furthermore, there is a significant enhancement in the discharge capacity and coulombic efficiency of the RFB when utilizing the OEGL. The results of this research establish a foundation for developing a sustainable and potentially affordable RFB for commercial production. The method also introduces another element to current biorefineries and pulp and paper mills, by functioning as inexpensive storage locations for variable renewable electricity.