Developing highly active and stable nitrogen reduction reaction (NRR) catalysts for NH3 electrosynthesis remains challenging. Herein, an unusual NRR electrocatalyst is reported with a single Zn(I) site supported on hollow porous N‐doped carbon nanofibers (Zn1N–C). The Zn1N–C nanofibers exhibit an outstanding NRR activity with a high NH3 yield rate of ≈16.1 µg NH3 h−1 mgcat−1 at −0.3 V and Faradaic efficiency (FE) of 11.8% in alkaline media, surpassing other previously reported carbon‐based NRR electrocatalysts with transition metals atomically dispersed and nitrogen coordinated (TM‐Nx) sites. 15N2 isotope labeling experiments confirm that the feeding nitrogen gas is the only nitrogen source in the production of NH3. Structural characterization reveals that atomically dispersed Zn(I) sites with Zn–N4 moieties are likely the active sites, and the nearby graphitic N site synergistically facilitates the NRR process. In situ attenuated total reflectance‐Fourier transform infrared measurement and theoretical calculation elucidate that the formation of initial *NNH intermediate is the rate‐limiting step during the NH3 production. The graphitic N atoms adjacent to the tetracoordinate Zn–N4 moieties could significantly lower the energy barrier for this step to accelerate hydrogenation kinetics duing the NRR.

The development of highly active electrocatalysts for e-NRR is obviously the key and thus has attracted increasing attention in recent years. Theoretical calculation predicted that an ideal e-NRR electrocatalyst should have suitable adsorption ability, i.e., neither too strongly nor too weakly, toward the N atom on catalytic surface, which offers an approximate guideline for designing highly efficient catalysts. [3] Catalysts based on noble metals are demonstrated to show e-NRR with favorable catalytic performances, but the high cost and less abundance of these catalysts hinder their widespread applications. [4] Much attention has thus been paid to developing transition metal alternatives. As we know, the catalytic activities of transition metals for e-NRR usually correlate strongly with the e g and t 2g orbitals' occupancy of catalysts, which to some extent determines the binding strength between the metal and nitrogen species. [5] Recently, transition metal single-atom catalysts (SACs) have been proved to be promising electrocatalysts for NH 3 synthesis. [6] Among them, iron-nitrogen-carbon materials (Fe-N-Cs) with atomically dispersed FeN 4 sites have received increasing attention as efficient e-NRR catalysts. [7] However, the electronegativity of the symmetrical adjacent nitrogen atoms around the metal site is relatively large, which makes The electrochemical nitrogen reduction reaction (e-NRR) is envisaged as alternative technique to theHaber-Bosch process for NH 3 synthesis. However, how to develop highly active e-NRR catalysts faces daunting challenges. Herein, a viable strategy to manipulate local spin state of isolated iron sites through S-coordinated doping (Fe SA -NSC) is reported. Incorporation of S in the coordination of Fe SA -NSC can induce the transition of spin-polarization configuration with the formation of a medium-spin-state of Fe (t 2g 6 e g 1), which is beneficial for facilitating e g electrons to penetrate the antibonding π-orbital of nitrogen. As a consequence, a record-high current density up to 10 mA cm −2 can be achieved, together with a high NH 3 selectivity of ≈10% in a flow cell reactor. Both experimental and theoretical analyses indicate that the monovalent Fe(I) atomic center in the Fe SA -NSC after the S doping accelerates the N 2 activation and protonation in the rate-determining step of *N 2 to *NNH.

Single-atom catalysts show great promise as non-precious electrocatalysts for CO 2 electroreduction reaction (CO 2 ER). However, it is still challenging to gain a fundamental understanding of the complicated dynamic behavior of CO 2 activation to achieve high product selectivity. Herein, the authors report an unusual iron single-atom catalyst, containing atomically dispersed Fe-N 4 species and Fe 3 C nanoparticles (NPs) (Fe 3 C|Fe 1 N 4 ). Having a fragmental-rockshaped nanocarbon architecture, isolated Fe-N 4 sites uniformly disperse with adjacent Fe 3 C NPs (<30 nm) in a carbon matrix. Benefiting from the strong coupling effect between Fe 3 C and Fe 1 N 4 and unique spatial nanostructure, Fe 3 C|Fe 1 N 4 displays exceptional CO 2 ER activity with a low onset potential of −0.3 V and high Faradaic efficiency of 94.6% at −0.5 V for CO production, acting as one of the most active Fe-N-C catalysts and even exceeding most other carbon supported non-precious metal NPs. Experimental observations discover that the excellent CO 2 ER activity of Fe 3 C|Fe 1 N 4 catalyst is attributable to the presence of Fe 3 C NPs that optimizes J CO of the coexisted Fe-N 4 active sites. In situ attenuated total reflectance-Fourier transform infrared analysis and theoretical calculations reveal that the Fe 3 C NPs strengthen the adsorption of CO 2 on the isolated Fe-N 4 sites to accelerate the formation of *COOH intermediate, and hence enhance the whole CO 2 ER performance.

Electrocatalytic reduction of CO 2 (CO 2 RR) to valueadded chemicals is of great significance for CO 2 utilization, however the CO 2 RR process involving multi-electron and proton transfer is greatly limited by poor selectivity and low yield. Herein, We have developed an atomically dispersed monovalent zinc catalyst anchored on nitrogenated carbon nanosheets (Zn/NC NSs). Benefiting from the unique coordination environment and atomic dispersion, the Zn/NC NSs exhibit as uperior CO 2 RR performance,f eaturing ah igh current density up to 50 mA cm À2 with an outstanding CO Faradaic efficiency of % 95 %. The center Zn I atom coordinated with three Natoms and one Natom that bridges over two adjacent graphitic edges (Zn-N 3+1 )isidentified as the catalytically active site.Experimental results reveal that the twisted Zn-N 3+1 structure accelerates CO 2 activation and protonation in the rate-determining step of *CO 2 to *COOH, while theoretical calculations elucidate that atomically dispersed Zn-N 3+1 moieties decrease the potential barriers for intermediate COOH* formation, promoting the proton-coupled CO 2 RR kinetics and boosting the overall catalytic performance.

Developing highly efficient carbon aerogels (CA) electrocatalysts based on transition metal-nitrogen sites is critical for the CO 2 electroreduction reaction (CO 2 RR). However, simultaneously achieving a high current density and high Faradaic efficiency (FE) still remains a big challenge. Herein, a series of unique 3D hierarchical cross-linked nanostructured CA with metal-nitrogen sites (MN, M = Ni, Fe, Co, Mn, Cu) is developed for efficient CO 2 RR. An optimal CA/N-Ni aerogel, featured with unique hierarchical porous structure and highly exposed M-N sites, exhibits an unusual CO 2 RR activity with a CO FE of 98% at −0.8 V. Notably, an industrial current density of 300 mA cm −2 with a high FE of 91% is achieved on CA/N-Ni aerogel in a flow-cell reactor, which outperforms almost all previously reported M-N/carbon based catalysts. The CO 2 RR activity of different CA/N-M aerogels can be arranged as Ni, Fe, Co, Mn, and Cu from high to low. In situ spectroelectrochemistry analyses validate that the rate-determining step in the CO 2 RR is the formation of *COOH intermediate. A ZnCO 2 battery is further assembled with CA/N-Ni as the cathode, which shows a maximum power density of 0.5 mW cm −2 and a superior rechargeable stability.