Single-atom catalysts have found considerable applications in the field of electrochemical CO 2 reduction reaction (CO 2 RR) due to their unique coordination environments. However, during the preparation of single-atom catalysts, some metal nanoparticles (NPs) are inevitably generated, which suffer from low selectivity in CO 2 RR. In this regard, complex postprocessing solution treatments are usually conducted to remove metal NPs using acid. Herein, we fabricated Ni(NC)-based catalysts composed of single Ni atoms and Ni NPs, both of which feature local Ni−N coordination via a simple Ni-metal organic framework (MOF)-assisted strategy. Based on X-ray photoelectron spectroscopy (XPS) and X-ray absorption fine structure (XAFS) spectroscopy measurements, nitrogen species in N-doped carbon have been demonstrated to be coordinated with surface nickel species to form Ni−N motifs, which makes Ni at a low-valent state for efficient CO 2 RR. Consequently, the catalyst exhibited high performances toward CO 2 RR with CO Faradic efficiencies (FE CO ) maintained over 90% from −0.65 to −0.90 V vs reversible hydrogen electrode (RHE). More importantly, the FE CO of 99% could be obtained at a considerable current density (j) of −160 mA cm −2 in a flow cell configuration. These findings suggest that regulating the surface environment of Ni species can activate the original inert reaction sites into active reaction sites, providing a promising avenue to design highperformance electrocatalysts for CO 2 RR.

Copper-based materials are efficient electrocatalysts for the conversion of CO 2 to C 2+ products,a nd most these materials are reconstructed in situ to regenerate active species. It is achallenge to precisely design precatalysts to obtain active sites for the CO 2 reduction reaction (CO 2 RR). Herein, we develop astrategy based on local sulfur doping of aCu-based metal-organic framework precatalyst, in whichthe stable CuÀ Smotif is dispersed in the framework of HKUST-1 (S-HKUST-1). The precatalyst exhibits ahigh ethylene selectivity in an Htype cell with am aximum faradaic efficiency (FE) of 60.0 %, and delivers acurrent density of 400 mA cm À2 with an ethylene FE up to 57.2 %i naflowc ell. Operando X-raya bsorption results demonstrate that Cu d+ species stabilized by the CuÀS motif exist in S-HKUST-1 during CO 2 RR. Density functional theory calculations indicate the partially oxidized Cu d+ at the Cu/Cu x S y interface is favorable for coupling of the *CO intermediate due to the modest distance between coupling sites and optimizedadsorption energy.

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Copper-based materials are efficient electrocatalysts for the conversion of CO 2 to C 2+ products,a nd most these materials are reconstructed in situ to regenerate active species. It is achallenge to precisely design precatalysts to obtain active sites for the CO 2 reduction reaction (CO 2 RR). Herein, we develop astrategy based on local sulfur doping of aCu-based metal-organic framework precatalyst, in whichthe stable CuÀ Smotif is dispersed in the framework of HKUST-1 (S-HKUST-1). The precatalyst exhibits ahigh ethylene selectivity in an Htype cell with am aximum faradaic efficiency (FE) of 60.0 %, and delivers acurrent density of 400 mA cm À2 with an ethylene FE up to 57.2 %i naflowc ell. Operando X-raya bsorption results demonstrate that Cu d+ species stabilized by the CuÀS motif exist in S-HKUST-1 during CO 2 RR. Density functional theory calculations indicate the partially oxidized Cu d+ at the Cu/Cu x S y interface is favorable for coupling of the *CO intermediate due to the modest distance between coupling sites and optimizedadsorption energy.

The electrochemical reduction reaction of CO2 provides a renewable method to close the carbon cycle and alleviate the global energy issue. Bi-based electrocatalysts present huge prospect of catalyzing formate-selective CO2...