regeneration of copper catalysts for long-term electrochemical CO reduction to multiple carbon products

The valorization of carbon dioxide (CO 2 ) via electrochemical CO 2 reduction (ECR) has attracted great interest as a pragmatic approach to tackle greenhouse gas emissions. Multiple carbon (C 2+ ) products, such as ethylene (C 2 H 4 ), ethanol (C 2 H 5 OH), and propanol (C 3 H 7 OH), are highly valuable chemicals and of great demand. Copper (Cu)-based catalysts are so far the only electrocatalytic materials that allow CO 2 reduction to C 2+ products at industrially relevant current densities (≥100 mA cm −2 ). However, most Cu-based catalysts are unstable in long-term reactions (>100 hours), with the main reasons being the potential-induced surface reconstruction, deposition of impurities, and catalyst aggregation and leaching, among others. Herein, we report an in situ catalyst regeneration strategy that can extend the operation time of Cu-based catalysts. By periodically adding segments of anodic currents to electrolysis, a Cu catalyst is partially oxidized to CuO x in each cycle, as confirmed by in situ Raman studies, leading to the restoration of the catalytically active sites for C 2+ products. We found that the oxidation current density and time significantly affect the selectivity and stability of Cu catalysts. Applying this strategy to a Cu catalyst - which is stable for ∼5 h towards C 2+ products during a continuous electroreduction under neutral-pH conditions, we were able to extend the operating time to ∼120 h in a flow cell system. The catalyst maintained a high faradaic efficiency (FE) for C 2 H 4 of ≥50% at a fixed cathodic current density of 150 mA cm −2 for over 60 h and continued to operate with a C 2 H 4 FE ≥ 40% for the entire length of the reaction time. This work opens up an avenue to enhance the stability of Cu electrocatalysts, via controlling the operating procedure during electrolysis. We report an in situ catalyst regeneration strategy that can extend the operation time of Cu-based catalysts for electrochemical CO 2 reduction many times.