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Abstract The quest for alternatives to Pt as an oxygen reduction electrocatalyst, possessing high activity, stability, and abundant reserves, holds great significance for H2/O2 fuel cells. Recently, metal‐nitrogen‐carbon (M‐N‐C) electrocatalysts have garnered substantial attention as promising substitutes. These electrocatalysts not only exhibit well‐defined structures but also offer the flexibility to adjust the central metal atoms and coordination atoms. It is beneficial in elucidating the active sites during the catalytic process and in the design of highly active electrocatalysts. In this review, the real active site of M‐N‐C electrocatalyst‐driven ORR is investigated in depth by in situ characterization techniques such as X‐ray absorption spectroscopy, Raman spectroscopy, Fourier‐transform infrared spectroscopy. It′s worth noting that the catalytic activity of M‐N‐C electrocatalysts originates from the dynamic evolution of electrocatalyst structure. Subsequently, we review various synthetic strategies, including the wet chemistry method, spatial confinement, and template‐assisted method, aimed at the rational design of M‐N‐C electrocatalysts. Moreover, recent progresses of M‐N‐C electrocatalysts with varying configurations, encompassing single‐atom, and double‐atom electrocatalysts are discussed, Finally, summary and perspectives on the development of M‐N‐C are provided.

Both nitrogen-doped carbon (NC) and metal-nitrogen-carbon (MNC) materials have been extensively investigated in lithium-sulfur batteries to alleviate the "shuttle effect". MNC are generally synthesized using NC as the parent material, wherein nitrogen atoms in NC serve as the "bridge" to coordinate with metal atoms. So far, an important scientific issue has not been settled: does the introduction of metal sites into NC certainly enhance the Li-S battery performance? In this work, NC and MNC materials derived from the same precursor, a nitrogen-rich porous polymer, are systematically compared as cathode hosts for Li-S battery through theoretical calculations and experimental investigation. Li-S cell with NC as the cathode sulfur host exhibits better cycle performance at low current densities (0.1 and 0.2C), whereas MNC materials predominate at higher current densities (such as 1C and 2C). Based on theoretical calculation and experimental results, it is concluded that the introduction of metal sites into NC through nitrogen bonding promoted the catalytic capability for faster sulfur redox reaction kinetics, whereas the adsorption energy toward polysulfides decreased. This work provides important guidance for more targeted design of advanced materials for lithium-sulfur battery application in the future., (© 2024 Wiley‐VCH GmbH.)

Developing efficient and robust metal-nitrogen-carbon electrocatalysts for oxygen reduction reaction (ORR) is of great significance for the application of hydrogen-oxygen fuel cells and metal-air batteries. Herein, a coordination engineering strategy is developed to improve the ORR kinetics and stability of cobalt-nitrogen-carbon (Co-N-C) electrocatalysts by grafting the oxygen-rich graphene quantum dots (GQDs) onto the zeolite imidazole frameworks (ZIFs) precursors. The optimized oxygen-rich GQDs-functionalized Co-N-C (G-CoNOC) electrocatalyst demonstrates an increased mass activity, nearly two times higher than that of pristine defective Co-N-C electrocatalyst, and retains a stability of 90.0% after 200 h, even superior to the commercial Pt/C. Comprehensive investigations demonstrate that the GQDs coordination can not only decrease carbon defects of Co-N-C electrocatalysts, improving the electron transfer efficiency and resistance to the destructive free radicals from H 2 O 2 , but also optimize the electronic structure of atomic Co active site to achieve a desired adsorption energy of OOH - , leading to enhanced ORR kinetics and stability by promoting further H 2 O 2 reduction, as confirmed by theoretical calculations and experimental results. Such a coordination engineering strategy provides a new perspective for the development of highly active noble-metal-free electrocatalysts for ORR., (© 2023 Wiley-VCH GmbH.)

Modulating the electronic structure of atomically dispersed active sites is promising to boost catalytic activity but is challenging to achieve. Here we show a cooperative Ni single-atom-on-nanoparticle catalyst (NiSA/NP) prepared via direct solid-state pyrolysis, where Ni nanoparticles donate electrons to Ni(i)-N-C sites via a network of carbon nanotubes, achieving a high CO current density of 346 mA cm -2 at -0.5 V vs RHE in an alkaline flow cell. When coupled with a NiFe-based anode in a zero-gap membrane electrolyzer, the catalyst delivers an industrially relevant CO current density of 310 mA cm -2 at a low cell voltage of -2.3 V, corresponding to an overall energy efficiency of 57 %. The superior CO 2 electroreduction performance is attributed to the enhanced adsorption of key intermediate COOH* on the electron-rich Ni single atoms, as well as a high density of active sites., (© 2022 Wiley-VCH GmbH.)

M-N-C (M = Fe, Co) are highly active nonprecious metal electrocatalysts for the oxygen reduction reaction (ORR) and other applications. Although their operation stability has been extensively studied in proton-exchange-membrane fuel cells, the storage stability that determines the performance maintenance before use has not yet been understood. Here, it is found that long-term exposure of M-N-C catalysts in air would cause surface oxidation and hydroxylation, resulting in significant decrease of ORR activity and fuel-cell performances. Hydrogen passivation is demonstrated to be an effective strategy to protect the atomic M-N 4 active sites and improve the storage stability of the catalysts. In addition, the hydrogen-termination can also reduce the ORR energy barrier and increase the utilization of active sites, leading to the improvements of fuel-cell activity and power density. Notably, these findings help to understand the storage-associated degradation and protection of M-N-C catalysts., (© 2021 Wiley-VCH GmbH.)

Metal-nitrogen-carbon (M-N-C) material with specifically coordinated configurations is a promising alternative to costly Pt-based catalysts. In the past few years, great progress is made in the studies of M-N-C materials, including the structure modulation and local coordination environment identification via advanced synthetic strategies and characterization techniques, which boost the electrocatalytic performances and deepen the understanding of the underlying fundamentals. In this review, the most recent advances of M-N-C catalysts with specifically coordinated configurations of M-N x (x = 1-6) are summarized as comprehensively as possible, with an emphasis on the synthetic strategy, characterization techniques, and applications in typical electrocatalytic reactions of the oxygen reduction reaction, oxygen evolution reaction, hydrogen evolution reaction, CO 2 reduction reaction, etc., along with mechanistic exploration by experiments and theoretical calculations. Furthermore, the challenges and potential perspectives for the future development of M-N-C catalysts are discussed., (© 2021 Wiley-VCH GmbH.)