Vitamin B12 Precatalyst Enables Molecular Cobalamin(II) Catalysis for Organodisulfide Anolytes in Aqueous Redox Flow Batteries.

Affordable and stable organodisulfide anolytes are attractive for long-duration aqueous redox flow batteries (ARFBs) for grid energy storage. However, the sluggish redox reactions involving the cleavage/formation of sulfur-sulfur (S─S) bonds cause severe polarization and limited capacity utilization, thus hindering the practical application of organodisulfide anolytes in ARFBs. Herein, we report a homogeneous catalysis strategy employing hydroxocobalamin (Vitamin B12, OHCbl) as an environmentally benign and biocompatible precatalyst which can enable molecular cobalamin(II) catalysis for organodisulfide anolytes. Cobalamin(II) generated in situ by electrochemical reduction of OHCbl bidirectionally accelerates the redox reactions of S─S bonds and significantly decreases the overpotential of the ARFB with SPS (bis(sodium sulfopropyl) disulfide) anolyte from 1.24 V to 0.36 V at 40 mA cm-2, boosting the energy efficiency from 18% to 66%. The OHCbl-catalyzed ARFB with 1.0 M SPS anolyte delivers a capacity of 51.45 Ah L-1 operated at 100% state of charge and remains stable for 850 cycles at 50 mA cm-2 with a low decay rate of 0.0189% per day. Moreover, a nearly saturated 1.3 M SPS-based ARFB achieves 96.2% capacity utilization, corresponding to 67.05 Ah L-1 delivered capacity. This cobalamin(II) catalysis strategy addresses the kinetic bottlenecks inherent to organodisulfide-based anolytes for ARFBs.