Redox-Mediated CO2 Electrolysis for Recovering Transmembrane Carbon Loss

Abstract

CO₂ electrolysis in alkaline media presents advantages by suppressing the competitive hydrogen evolution reaction (HER) and enhancing the CO₂ reduction selectivity. However, it suffers from the carbonation issue, leading to substantial carbon loss due to CO₂ transmembrane transport. To tackle this issue, we here put forward a redox mediator (RM)-coupled electrolysis strategy. By integrating a highly reversible redox couple, this approach spatially separates the cathodic CO₂ reduction and the anodic oxygen evolution reactions (OERs) into two electrolyzers, thereby enabling the recovery and reuse of transmembrane CO₂. Anthraquinone-2,7-disulfonic acid (AQDS) was chosen as the redox mediator owing to its suitable redox potential, excellent electrochemical reversibility, high solubility, and nontransmembrane shuttling characteristics. It allowed the RM-coupled electrolysis system to operate continuously at 100 mA/cm², maintaining a high Faradaic efficiency (FE) for CO₂-to-CO conversion consistently around 90%, while effectively capturing the transmembrane CO₂. This proof-of-concept demonstration validates the feasibility of RM-coupled electrolysis and highlights its significant potential to advance the practical application of CO₂ electrolysis.