Operando Constructing Cu/Cu2O Electrocatalysts for Efficient CO2 Electroreduction to Ethanol: CO2-Assisted Structural Evolution of Octahedral Cu2O by Operando CV Activation

Oxide-derived Cu (OD-Cu) exhibits unique and excellent C2 product selectivity (ethanol, ethylene, etc.) in the field of electrocatalytic reduction reaction of CO2 (eCO2RR), which has a great application value in realizing effective storage of renewable energy and the artificial closed carbon cycle. However, the Cu2O structure encounters complex structure evolution under negative potential conditions, making it difficult to obtain the specific active structures. Here, we found an operando activation strategy for the OD-Cu catalyst based on the cyclic voltammetry (CV) process conducted in CO2-saturated solution. Assisted by an interval eCO2RR, the sluggish octahedral–Cu2O (o-Cu2O) evolves into active Cu/Cu2O–CV, with the formed "metallic Cu" uniformly anchoring on o-Cu2O and accompanied by rich Cuδ+–Cu0 grain boundaries. Combined with in situ and ex situ characterization, compared to o-Cu2O, Cu/Cu2O–CV significantly promoted the formation of C2 products (FEC2 increased from 17.13 to 73.44%). By enhancing the adsorption of CO* and subsequently the formation of O*C*COH intermediates, the Faraday efficiency for ethanol was significantly improved from 5.15% (on o-Cu2O) to 56.56% (on Cu/Cu2O–CV). Our study provides evidence for a previously unexplored function of CO2 in the evolution of o-Cu2O catalysts into highly active structures for the generation of multicarbon products, opening a pathway for the rational design of future catalysts for the electrochemical reduction of CO2.