Atomically Precise Copper Nanoclusters for Highly Efficient Electroreduction of CO2 towards Hydrocarbons via Breaking the Coordination Symmetry of Cu Site

Abstract

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 CO₂ electroreduction from HCOOH/CO to higher-valued hydrocarbons. An atomically well-defined Cu₆ NC with symmetry-broken Cu-S₂ N₁ active sites (named Cu₆ (MBD)₆ , 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-S₃ sites, the Cu₆ (MBD)₆ with Cu-S₂ N₁ coordination structure shows a high Faradaic efficiency toward hydrocarbons of 65.5 % at -1.4 V versus the reversible hydrogen electrode (including 42.5 % CH₄ and 23 % C₂ H₄ ), with the hydrocarbons partial current density of -183.4 mA cm^-2 . Theoretical calculations reveal that the symmetry-broken Cu-S₂ N₁ sites can rearrange the Cu 3d orbitals with $d_{x^2-y^2}$ 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 CO₂ RR towards highly-valued products.

Keywords: Atomically Precise Nanoclusters; C2H4; CH4; CO2 Electrocatalysis; Copper.