CO2 Reduction by Transition‐Metal Complex Systems: Effect of Hydrogen Bonding on the Second Coordination Sphere

Abstract Homogeneous electrocatalysts typified by transition‐metal complex show transcendent potency in efficient energy catalysis through molecular design. For example, metal complexes with elaborate design performed wonderful activity and selectivity for electrocatalytic CO 2 reduction. Primary coordination sphere of metal complexes plays a key role in regulating its intrinsic redox properties and catalytic activity. However, the overall reduction efficiency of CO 2 is also bound up with the substrate activation process. Transition‐metal complexes are hoped to exhibit reasonable redox potential, reactive activity, and stability, while binding and activating CO 2 molecules to achieve efficient CO 2 reduction. Construction of second coordination sphere, especially hydrogen‐bonding network of transition‐metal complexes, is reported to be the “kill two birds with one stone” strategy to realize efficient CO 2 reduction catalysis via systematic catalyst properties modulation and substrate activation. Herein, we present recent progress on the construction of hydrogen‐bonding network in the second coordination sphere of metal complexes by ligand modification or the introduction of exogenous organic ligand, and the resulted productive enhancement of the catalytic performance of metal complexes by the improvement of adsorption capacity and activation of CO 2 , proton transfer rate, and stability of reaction intermediates, and so forth.