Metal heteroatom doped carbon materials display remarkable catalytic performance in the electrochemical CO 2 reduction (ECR) because the doped heteroatoms can significantly change the local density of state and electronic structure of carbon, which induces charge polarization or structural defects. Herein, we synthesized S-doped Ni II -triazolate precursors with high purity and crystallinity through a simple one-step hydrothermal method. The high-temperature pyrolysis process produced a series of Ni−S−C T (T = 800, 900, 1000 °C) materials with Ni 3 S 2 as the main component. It resulted in significant carbon structure defects in the catalyst, which increased the specific surface area and pore volume, providing a basis for improving the ECR activity. Through the structural characterizations of powder X-ray diffraction (PXRD), Raman, X-ray photoelectron (XPS), Brunauer−Emmett−Teller (BET), transmission electron microscopy (TEM), and electrochemical characterizations of linear sweep voltammetry (LSV), chronoamperometry (i−t curve), electrochemical impedance spectroscopy (EIS), and electrochemical active surface area (ECSA), as well as gaseous product analysis, we can build the structural-performance relationship. Ni−S−C T catalysts all reached the highest CO Faraday efficiency at −1.5 V vs Ag/AgCl potential, among which Ni−S−C 1000 exhibited the best catalytic activity (FE CO of 66.6% and j CO of 1.28 mA/ cm 2 ). It also displayed excellent stability and recyclability, which could realize the efficient reuse of the catalyst. In addition, the density functional theory (DFT) calculation was carried out on Ni 3 S 2 to illustrate the ECR activity origination. It is the first report on Ni 3 S 2 -based catalysts in the application of ECR.

Storing and hydrogenating CO 2 to CH 4 is an efficient solution to alleviate the greenhouse effect and energy shortage. This work demonstrated that the CaO-captured CO 2 could be selectively converted to CH 4 by Ni-and hydrogenassisted calcium looping (CaL) processes in a batch reactor. The Ni/CaO composite was first synthesized in one step at room temperature by calcium-induced hydrogenation of Ni-mixed calcium carbonate without the use of any solvent and CO 2 emission. The CO 2 capture properties over the Ni/CaO composite and the methanation properties of the Ni/CaCO 3 composite produced after CO 2 capture were then studied in a batch reactor. It was proved that the CO 2 capture properties of CaO can be improved, the CaO recovering temperature can be significantly lowered, and valuable CH 4 can be selectively produced by Ni-and hydrogen-assisted calcium looping processes at moderate/high temperature. The 68.58% methane yield and 100% methane selectivity were achieved under relatively mild conditions. After five Ni-and hydrogen-assisted CaL processes, the methane yield still reaches 45%. This study offers a novel energy-saving CaL process, which can be utilized for facile and selective conversion of the CaO-captured CO 2 to CH 4 .

CO2 capture and selective methanation were realized over a greenly prepared Ni/CaO/Al2O3 composite at as low as 200 °C under static pressure conditions.

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