Lignin as redox-targeted catalyst for the positive vanadium electrolyte Electrochemistry Communications

Vanadium Redox Flow Batteries (VRFBs) are promising candidates for large- scale energy storage applications however, there are still some obstacles that need to be overcome such as their low energy density (25-30 Wh L-1 for a 1.8 M electrolyte), high cost and large environmental impact due to corrosiveness and the unsustainability of vanadium. To address these challenges, we introduce lignin as a low-cost electrocatalyst and capacity booster for the positive electrolyte. Coated on a glassy carbon electrode, lignin showed electrocatalytic abilities and improved the electrochemical reversibility of the VO2+/ redox couple significantly. In charge and discharge cycles volumetric capacities of 28 Ah L-1 (charge) and 23.5 Ah L-1 (discharge) were achieved with a 0.9 M concentrated vanadium electrolyte which surpassed the maximum theoretical capacity of 24.1 Ah L-1 in the charge. This demonstrates an increase of 7.5 Ah L-1 and 9 Ah L-1 for the charge and discharge cycles, respectively, compared to a pristine carbon felt electrode. This work showcases the noteworthy influence of lignin on vanadium and opens new possibilities for VRFB chemistry.