Mechanistic Understanding of CO₂ Reduction Reaction (CO2RR) Toward Multicarbon Products by Heterogeneous Copper-Based Catalysts

In the recent years, significant progress has been made toward designing active and selective catalysts for electrochemical CO2 reduction, with particular interest focused on the two major C2 products—ethylene and ethanol. Numerous efforts have been made to enhance the understanding of the heterogeneous copper-based CO2 reduction mechanisms by computational studies. Here we provide a critical assessment of various proposed scenarios of the initial and post C–C coupling steps that result in either ethylene or ethanol. In silico rationalization of the parameters controlling the product selectivity, such as the catalyst structure and composition (Cu facets, the presence of defective sites and/or subsurface oxygen atoms, or the interplay with a second metal) and the reaction conditions (pH, applied potential, and electrolyte), is provided. A comprehensive scheme combining the proposed pathways is derived, and the issues that are still under debate and require further investigations are highlighted.