Inline Capacity Recovery of Vanadium Flow Batteries via Methanol-Mediated Catalytic Rebalancing

Vanadium flow batteries (VFBs) are promising for grid-scale, long-duration energy storage, but their long-term operation is limited by capacity decay from electrolyte imbalance, especially oxidative valence drift caused by parasitic side reactions. Here, we report an inline capacity recovery strategy based on methanol-mediated catalytic rebalancing during VFB operation. As a compact chemical electron carrier, methanol delivers 6 electrons per molecule upon full oxidation, providing high gravimetric electron density and low materials cost. A methanol-fed Pt/C side-stream reactor was integrated with the VFB posolyte loop to reduce excess VO 2 + and rebalance the electrolyte valence. Spectroscopic analyses confirm quantitative conversion without detectable residual methanol-derived organic species under the testing conditions. An inline recovery was triggered whenever capacity retention decreased to ~95%, repeatedly restoring the capacity to >99% of its initial value during 30 days of continuous operation. This strategy provides a practical route for continuous VFB capacity maintenance and electrolyte lifecycle management.