Exploring Redox Mediated Water Electrolysis Using Mn – V Redox Flow Batteries

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Hydrogen gas is widely regarded as a key energy carrier for achieving net-zero carbon emissions by 2050, with green hydrogen, produced via electrochemical water splitting, being central to this goal. However, the production of green hydrogen from renewable sources remains limited, accounting for ~4% of global hydrogen production in 2021 [1]. Water electrolysis systems, while theoretically operating at 1.23 V, require higher voltages in practice due to membrane gas crossover, which reduces efficiency and raises costs [2]. This study explores a novel approach to supplement green hydrogen generation through indirect water splitting, where soluble redox mediators, primarily used for energy storage, extend their capability to perform Redox-Mediated Hydrogen Evolution Reactions (RM-HER) in external catalytic reactors [3,4]. Building on prior work that established a stable manganese-vanadium flow battery for energy storage, the current research shifts focus to the anolyte (V3+/V2+) redox mediator for RM-HER [5]. The study aims to refine electrolyte composition to enhance hydrogen gas yields and efficiencies in flow-assisted redox-mediated electrolysis systems. To assess the relationship between faradaic gas efficiency and coulombic efficiency for cycled electrolytes, we utilize ultramicroelectrodes to uncover key factors—such as the state of charge (SOC) of the anolyte and manganese crossover—that affect the onset potential of RM-HER. Furthermore, the study examines the role of different electrocatalysts to identify ideal materials that can withstand the effects of manganese while maximizing hydrogen generation. We believe that the electrochemical environment and improved electrocatalytic surfaces are central to understanding the efficiency of hydrogen gas production. The electrochemical characterization techniques (e.g., cyclic voltammetry and electrochemical impedance spectroscopy) utilized in this study help evaluate the reusability of the electrolyte, providing insights into the system’s potential for a seamless switch between these two complementary use-case scenarios: energy storage and RM-HER. This approach could lead to a more efficient, cost-effective, and scalable process for hydrogen production, contributing to the broader adoption of green hydrogen and sustainable solutions. References Emanuele Taibi, et al., Green Hydrogen Cost Reduction: Scaling up Electrolysers to Meet the 1.5⁰C Climate Goal, International Renewable Energy Agency - IRENA, 2020. Symes, M.D. and L. Cronin, Decoupling hydrogen and oxygen evolution during electrolytic water splitting using an electron-coupled-proton buffer. Nature Chemistry, 2013. 5(5): p. 403-409. Reynard, D. and H. Girault, Combined hydrogen production and electricity storage using a vanadium manganese redox dual-flow battery. Cell Reports Physical Science, 2021. 2(9): p. 16. Reynard, D., et al., Vanadium-Manganese Redox Flow Battery: Study of MnIII Disproportionation in the Presence of Other Metallic Ions. Chemistry – A European Journal, 2020. 26(32): p. 7250-7257. Chaurasia, S., et al., Investigating Manganese–Vanadium Redox Flow Batteries for Energy Storage and Subsequent Hydrogen Generation. ACS Applied Energy Materials, 2024.

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