within acceptable limits are needed. Among the many possible solutions, electrochemical CO 2 reduction (ECR) offers a potentially sustainable approach not only for depressing CO 2 concentration but also converting it into fuels and commodity chemicals. [2] Unfortunately, the CO chemical bond in CO 2 (≈806 kJ mol −1 ) is thermodynamically very stable and its conversion is an uphill energy process with a high activation barrier. Moreover, during electrochemical reduction of CO 2 , the hydrogen evolution reaction (HER) inevitably occurs as a competing reaction, which is a major stumbling block for CO 2 reduction especially in aqueous electrolytes. [3] From these scenarios, robust catalysts that can selectively reduce CO 2 in lieu of protons at high turnover frequency (TOF) and faradaic efficiency (FE) for CO 2 reduction are desired.Since Hori's pioneering study on electroreduction of CO 2 in the 1980s, [4] Cu, [5] Au, [6] Ag, [7] Zn, [8] Sn, [9] and Bi [10] among others, have been widely investigated for electrocatalysis of CO 2 reduction, due to their promising capability to convert CO 2 into valuable chemicals and fuels while the HER is largely suppressed. Earth-abundant first-row transition metals such as Fe, Co, and Ni, however, are highly active for HER and also easily Electrochemical reduction of carbon dioxide (CO 2 ) to fuels and value-added industrial chemicals is a promising strategy for keeping a healthy balance between energy supply and net carbon emissions. Here, the facile transformation of residual Ni particle catalysts in carbon nanotubes into thermally stable single Ni atoms with a possible NiN 3 moiety is reported, surrounded with a porous N-doped carbon sheath through a one-step nanoconfined pyrolysis strategy. These structural changes are confirmed by X-ray absorption fine structure analysis and density functional theory (DFT) calculations. The dispersed Ni single atoms facilitate highly efficient electrocatalytic CO 2 reduction at low overpotentials to yield CO, providing a CO faradaic efficiency exceeding 90%, turnover frequency approaching 12 000 h −1 , and metal mass activity reaching about 10 600 mA mg −1 , outperforming current state-of-the-art single atom catalysts for CO 2 reduction to CO. DFT calculations suggest that the Ni@N 3 (pyrrolic) site favors *COOH formation with lower free energy than Ni@N 4 , in addition to exothermic CO desorption, hence enhancing electrocatalytic CO 2 conversion. This finding provides a simple, scalable, and promising route for the preparation of low-cost, abundant, and highly active single atom catalysts, benefiting future practical CO 2 electrolysis.

Metal-organic frameworks (MOFs) are regardeda sp romising materials for CO 2 adsorption,which is an importantstep in CO 2 electrochemical reduction.I nt his work, zeolitic imidazolate framework (ZIF-8) nanomaterials were synthesized with various zinc sourcesa nd used as electrocatalystsf or CO 2 reduction to CO. Among them, ZIF-8,p repared using ZnSO 4 ,d elivers the best catalytic activity towards CO 2 electroreduction,w ith 65 % CO yield. The main catalytic centerc an be attributed to the discrete Zn nodes in ZIF-8. Electrolytes are important in increasingt he CO selectivity,a nd NaCl is the best suitablee lectrolyte duetof acile anion exchange.The increasing consumption of fossil resources is broadly regarded as ac ausef or the rising levels of CO 2 in the atmosphere, which leads to energy and environmental problems. [1][2][3] Electrochemical reduction of CO 2 ,u sing electricity from renewable resources, is ap otentially "clean"s trategy to obtain fuels and chemicals under mild conditions. [4][5][6][7][8] However, efficient and robust catalysts operatinga ts mall over-potentials with high selectivity and efficiency are still required for technology commercialization.To address these problems, av ariety of electrocatalysts based on metal and metallicc omplexesh as been developed. Amongt hem, noble metals,s uch as Au, [9,10] Ag, [11] and Pd, [12,13] have shown highF aradaic efficiencies for CO production;h owever,t he scarcity andh igh cost hinder their broad use in CO 2 electro-reduction. It is necessary to develop earth-abundant materials as potent catalysts for CO 2 electro-reduction. Metalorganic frameworks (MOFs)a re promising materials for diverse catalytic conversions. [14,15] Zeolitic imidazolate frameworks (ZIFs), as as ubclass of MOFs, are formed in zeolite topologies with metal ions and imidazolate ligands. [16] Due to their large specific surfacea rea, tunable porosity,a nd tailorable functionality,Z IFs emerged as versatile materials for catalysis,s eparation, energy storage, and so on. [17][18][19] Among various ZIFs, ZIF-8 have been further investigated ase lectrode materials fors upercapacitors, water electrolysis,p hotocatalysts, etc. [20][21][22][23] ZIF-8 served as porous electrode material for supercapacitora sr eported by Yamauchi et al, and delivered high electrochemical capacitance and good stability. [24] It can be calcined to form C, N-doped ZnO for use in dye degradationa nd water oxidation. [25] Besides, ZIF-8 possessesh igh CO 2 adsorption properties, which is an important step for CO 2 electrochemical reduction. [26] Recently,u sing MOFs for CO 2 reduction has just emerged and showed considerable catalytic performances. [28][29][30] Yet, ZIF-8 as ac atalysis material for CO 2 electrochemical reduction has not been reported.In this work, several ZIF-8 nanomaterials have been synthesized to investigate the aqueous electrocatalytic reduction of CO 2 ,e xploitingu nique properties such as larges urface area, uniform pore size, well-defined morphology,a nd strong coordination between me...

Single‐atom Co catalyst Co‐Tpy‐C with well‐defined sites is synthesized by pyrolysis of a Co terpyridine (Tpy) organometallic complex. The Co‐Tpy‐C catalyst exhibits excellent activity for the electrochemical CO2 reduction reaction in aqueous electrolyte, with CO faradaic efficiency (FE) of over 95% from −0.7 to −1.0 V (vs RHE). By comparison, catalysts without Co or Tpy ligand added do not show any high CO FE. When simulated flue gas with 15% of CO2 is used as the source of CO2, CO FE is kept at 90.1% at −0.5 V versus RHE. During gas phase flow electrolysis using simulated flue gas, the CO partial current density is further increased to 86.4 mA cm−2 and CO FE reached >90% at the cell voltage of 3.4 V. Experiments and density functional theory calculations indicate that uniform single‐atom Co–N4 sites mainly contribute to the high activity for CO2 reduction.