Driving a deficient cathodic environment using anode to control selectivity for CO₂ electroreduction

The anode has not been extensively studied in electrochemical CO₂ reduction reaction (CO₂RR) systems because it is believed to have no significant effect on the catalytic selectivity and activity of the cathode. Herein, we report that the anode can indeed influence the catalytic activity of the CO₂RR by regulating the transfer of water and ions in a membrane electrode assembly. Despite employing identical cathode conditions, we observed optimal ethylene production at different current densities for distinct anode substrates: carbon paper (CP) and Ti meshes (TM). TM shows optimal ethylene Faradaic efficiency (31.1 %) in the high current density region, while CP demonstrates optimal ethylene Faradaic efficiency (20 %) in the low current density region. Based on the results of in situ/operando analysis and transparent cell tests, CP creates an environment deficient in water and cations, thereby promoting local pH effects. Consequently, this leads to a higher valence state of Cu during the CO₂RR, resulting in increased catalytic activity for ethylene production. However, in the high-current-density region, the catalytic activity of CP degrades due to the uneven distribution of the reaction. Our study contributes to a deeper understanding of the reaction environment for CO₂RR and offers insights for optimizing the catalytic activity of CO₂RR systems.