Highly Ethylene-Selective Electrocatalytic CO2 Reduction Enabled by Isolated Cu-S Motifs in Metal-Organic Framework Based Precatalysts.

Copper-based materials are efficient electrocatalysts for the conversion of CO2 to C2+ products, and most these materials are reconstructed in situ to regenerate active species. It is a challenge to precisely design precatalysts to obtain active sites for the CO2 reduction reaction (CO2 RR). Herein, we develop a strategy based on local sulfur doping of a Cu-based metal-organic framework precatalyst, in which the stable Cu-S motif is dispersed in the framework of HKUST-1 (S-HKUST-1). The precatalyst exhibits a high ethylene selectivity in an H-type cell with a maximum faradaic efficiency (FE) of 60.0 %, and delivers a current density of 400 mA cm-2 with an ethylene FE up to 57.2 % in a flow cell. Operando X-ray absorption results demonstrate that Cuδ+ species stabilized by the Cu-S motif exist in S-HKUST-1 during CO2 RR. Density functional theory calculations indicate the partially oxidized Cuδ+ at the Cu/Cux Sy interface is favorable for coupling of the *CO intermediate due to the modest distance between coupling sites and optimized adsorption energy.