Electrocatalytic reduction of CO₂ and CO to multi-carbon compounds over Cu-based catalysts

The electrocatalytic reduction of CO₂ with H₂O to multi-carbon (C₂₊) compounds, in particular, C₂₊ olefins and oxygenates, which have versatile applications in the chemical and energy industries, holds great potential to mitigate the depletion of fossil resources and abate carbon emissions. There are two major routes for the electrocatalytic CO₂ reduction to C₂₊ compounds, i.e., the direct route and the indirect route via CO. The electrocatalytic CO₂ reduction to CO has been commercialised with solid oxide electrolysers, making the indirect route via CO to C₂₊ compounds also a promising alternative. This tutorial review focuses on the similarities and differences in the electrocatalytic CO₂ and CO reduction reactions (CO₂RR and CORR) into C₂₊ compounds, including C₂H₄, C₂H₅OH, CH₃COO^- and n-C₃H₇OH, over Cu-based catalysts. First, we introduce the fundamental aspects of the two electrocatalytic reactions, including the cathode and anode reactions, electrocatalytic reactors and crucial performance parameters. Next, the reaction mechanisms, in particular, the C-C coupling mechanism, are discussed. Then, efficient catalysts and systems for these two reactions are critically reviewed. We analyse the key factors that determine the selectivity, activity and stability for the electrocatalytic CO₂RR and CORR. Finally, the opportunities, challenges and future trends in the electrocatalytic CO₂RR and CORR are proposed. These insights will offer guidance for the design of industrial-relevant catalysts and systems for the synthesis of C₂₊ olefins and oxygenates.