Recent developments in electro/photo chemical reduction of CO2 by ligand-protected Cu nanoclusters with precise crystal structures

CO2 is a thermodynamically and kinetically stable molecule with its standard Gibbs free energy of formation (ΔGfo) of -394.4 kJ·mol-1 at 298 K and a highly negative first-electron reduction potential (Eo) of -1.90 V vs. standard hydrogen electrode (SHE) in aqueous solution. Therefore, its thermal reduction requires high temperatures to overcome the unfavorable thermodynamics and kinetics. Even so, electrochemical CO2 reduction reactions (ECO2RR) and photochemical CO2 reduction reactions (PCO2RR) have been demonstrated to be highly effective in terms of ambient operative conditions, conversion efficiency, and capacity to generate a wide range of value-added carbon-based fuels. However, to drive the ECO2RR/PCO2RR, highly efficient and atomically well-defined catalysts with customized optimizations are required. Thanks to the specific and uniform catalytic active sites located on the metal nanocluster surface/interface defined by their precise atomic structure, the ligand-protected atomically precise Cu nanoclusters have been shown to drive the CO2 reduction reaction (CO2RR) to various valuable C1, C2, and C2+ products. The current status of the synthesis and the ECO2RR and PCO2RR catalyzed by ligand-protected Cu nanoclusters with precise crystal structures is reviewed in this article.