A Regenerative Redox‐Mediated Electrolysis System (RReMES) for Efficient Reduction of Water Electrolysis Overpotentials

Abstract The overpotential in water electrolysis (WE) is directly linked to an increase in operational costs, making its reduction a critical challenge. To address this issue, extensive research has been conducted over the decades to develop highly efficient catalysts for both the hydrogen and anodes to minimize overpotential. In particular, the oxygen evolution reaction (OER) at the cathode has been recognized as a rate limiting process of WE. However, most known high‐efficiency OER catalysts are rare metal‐based materials posing challenges related to resource limitations and high costs. In this study, a Regenerative Redox‐Mediated Electrolysis System (RReMES) is proposed, which enables hydrogen production at a significantly lower overpotential compared to conventional water electrolysis utilizing the OER. The reduction of WE overpotential is achieved by introducing hydroquinone (HQ) into the electrolyte, facilitating the oxidation of hydroquinone instead of the OER. HQ is a redox‐active species with a lower oxidation potential than the OER and is oxidized to benzoquinone (BQ). Since BQ can be photochemically regenerated back to HQ by light, maintaining a low overpotential is feasible through the continuous illumination of light. This paper discusses the system configuration, WE performances, and impact of redox active agents on the performance of RReMES.