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

Abstract

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.