Redox-Mediated CO2 Electrolysis for Recovering Transmembrane Carbon Loss.

CO2 electrolysis in alkaline media presents advantages by suppressing the competitive hydrogen evolution reaction 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 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 non-transmembrane shuttling characteristics. It allowed the RM-coupled electrolysis system to operate continuously at 100 mA/cm2, maintaining a high faradaic efficiency 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.