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...

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Pt, RuO 2 , IrO 2 , etc.) are the most efficient hydrogen evolution reaction (HER) electrocatalysts, but their high cost and low abundance limit their industrial applications. [9][10][11][12] Therefore, it is significant to prepare non-precious metal electrocatalysts with low cost and high performance.Transition metal-based materials, such as alloys, sulfides, hydroxides, nitrides, oxides, and so on, have been widely used as HER electrocatalysts in alkaline water electrolysis. Among them, nickelmolybdenum alloy-based materials are considered to be the most promising and cheapest substitutes for noble metal catalysts in alkaline environments because nickel sites are good water dissociation centers and molybdenum sites feature excellent hydrogen adsorption properties. [13][14][15][16] However, the molybdenum in the nickel-molybdenum alloy is very easy to precipitate, which significantly limits the further application of the nickelmolybdenum alloy under the high current density. [17] Recently, researchers found that the larger negative binding energy of transition metal hydroxides can facilitate the HER process by reducing the adsorption energy of H 2 O and the Gibbs free energy of adsorbed H*. [18][19][20] In particular, cobalt hydroxides (Co(OH) x ), a highly active Volmer promoter, can promote water splitting through the instantaneous formation of intermediate H* atoms during alkaline HER process. Furthermore, twodimensional (2D) layered Co (OH) x with relatively open structure facilitates the diffusion of products and accelerates proton-coupled electron transfer. [21][22][23] To generate Co(OH) x promoters for alkaline HER, the metallic cobalt (Co 0 ) precatalyst components usually undergo rearrangement of the surface structure under the action of electrons to form hydroxide/oxyhydroxide species during the electrochemical process. [24] Thus, metallic Co 0 can be deposited on the surface of the electrocatalyst in advance, and then the in situ grown Co(OH) x catalyst can be obtained by electrochemical activation process. To meet practical industrial applications, the precatalyst can be constructed on 3D porous substrates such as nickel foam (NF) to avoid the agglomeration of active materials and ensure a certain mechanical strength, which provides a certain prerequisite for the stable use of electrocatalysts at high current densities. [25][26][27][28] Herein, we report an electrocatalyst synthesis strategy, where the alkaline HER performance was greatly enhanced by constructing a

Bismuth-based materials (e.g., metallic, oxides and subcarbonate) are emerged as promising electrocatalysts for converting CO2 to formate. However, Bio-based electrocatalysts possess high overpotentials, while bismuth oxides and subcarbonate encounter stability issues. This work is designated to exemplify that the operando synthesis can be an effective means to enhance the stability of electrocatalysts under operando CO2RR conditions. A synthetic approach is developed to electrochemically convert BiOCl into Cl-containing subcarbonate (Bi2O2(CO3)xCly) under operando CO2RR conditions. The systematic operando spectroscopic studies depict that BiOCl is converted to Bi2O2(CO3)xCly via a cathodic potential-promoted anion-exchange process. The operando synthesized Bi2O2(CO3)xCly can tolerate − 1.0 V versus RHE, while for the wet-chemistry synthesized pure Bi2O2CO3, the formation of metallic Bio occurs at − 0.6 V versus RHE. At − 0.8 V versus RHE, Bi2O2(CO3)xCly can readily attain a FEHCOO- of 97.9%, much higher than that of the pure Bi2O2CO3 (81.3%). DFT calculations indicate that differing from the pure Bi2O2CO3-catalyzed CO2RR, where formate is formed via a *OCHO intermediate step that requires a high energy input energy of 2.69 eV to proceed, the formation of HCOO− over Bi2O2(CO3)xCly has proceeded via a *COOH intermediate step that only requires low energy input of 2.56 eV.