Atomically Precise Copper Nanoclusters for Highly Efficient Electroreduction of CO towards Hydrocarbons via Breaking the Coordination Symmetry of Cu Site.

We propose an effective highest occupied d-orbital modulation strategy engendered by breaking the coordination symmetry of sites in the atomically precise Cu nanocluster (NC) to switch the product of CO electroreduction from HCOOH/CO to higher-valued hydrocarbons. An atomically well-defined Cu NC with symmetry-broken Cu-S N active sites (named Cu (MBD) , MBD=2-mercaptobenzimidazole) was designed and synthesized by a judicious choice of ligand containing both S and N coordination atoms. Different from the previously reported high HCOOH selectivity of Cu NCs with Cu-S sites, the Cu (MBD) with Cu-S N coordination structure shows a high Faradaic efficiency toward hydrocarbons of 65.5 % at -1.4 V versus the reversible hydrogen electrode (including 42.5 % CH and 23 % C H ), with the hydrocarbons partial current density of -183.4 mA cm . Theoretical calculations reveal that the symmetry-broken Cu-S N sites can rearrange the Cu 3d orbitals with as the highest occupied d-orbital, thus favoring the generation of key intermediate *COOH instead of *OCHO to favor *CO formation, followed by hydrogenation and/or C-C coupling to produce hydrocarbons. This is the first attempt to regulate the coordination mode of Cu atom in Cu NCs for hydrocarbons generation, and provides new inspiration for designing atomically precise NCs for efficient CO RR towards highly-valued products.