English

• INTRODUNTION

  The increasing demand for energy and the aggravation of environmental problems urge scientists not only to find new sources of clean and sustainable energy, but also to develop new energy conversion technologies with high-efficiency, low cost and sustainability.^{[1, 2]} The hydrogen energy is considered as a clean and sustainable alternative to conventional fossil fuels.^{[3, 4]} The water splitting can realize the transformation of electric energy to chemical energy.^[5] Fuel cells, in turn, can convert the chemical energy into electricity.^[6] The reactants and products in the whole reaction process only involve water, hydrogen, and oxygen.^[7] This ensures the cleanliness and environmental requirements of such devices.^[8] Four important basic semi-reactions, namely hydrogen evolution reaction (HER), oxygen evolution reaction (OER), ^{[9, 10]} hydrogen oxidation reaction (HOR) and oxygen reduction reaction (ORR), usually occur in electrolytic water devices, fuel cells, zinc-air cells, and so on.^[11] In acidic or basic electrolytes, the reaction process is usually as follows:

  HER/OER: $ {\text{2}}{{\text{H}}}_{{\text{2}}}{\text{O →}}{{\text{2H}}}_{{\text{2}}}{\text{+}}{{\text{O}}}_{{\text{2}}} $

  Basic electrolyte:

  $ {{\text{4OH}}}^{{\text{-}}}{\text{→}}{{\text{O}}}_{{\text{2}}}{\text{+ 2}}{{\text{H}}}_{{\text{2}}}{\text{O +}}{{\text{4e}}}^{{\text{-}}}\;{\text{(OER)}} $

  $ {{\text{4H}}}_{{\text{2}}}{\text{O +}}{{\text{4e}}}^{{\text{-}}}{\text{→}}{{\text{2H}}}_{{\text{2}}}{\text{+ 4}}{{\text{OH}}}^{{\text{-}}}\;{\text{(HER)}} $

  Acid electrolyte:

  $ {{\text{2H}}}_{{\text{2}}}{\text{O →}}{{\text{O}}}_{{\text{2}}}{\text{+ 4}}{{\text{H}}}^{{\text{+}}}{\text{}}{\text{+ 4}}{{\text{e}}}^{{\text{-}}}\;{\text{(OER)}} $

  $ {{\text{4H}}}^{{\text{+}}}{\text{+ 4}}{{\text{e}}}^{{\text{-}}}{\text{→}}{{\text{2H}}}_{{\text{2}}}\;{\text{(HER)}} $

  ORR/HOR: $ {{\text{2H}}}_{{\text{2}}}{\text{+}}{{\text{O}}}_{{\text{2}}}{\text{→}}{{\text{2H}}}_{{\text{2}}}{\text{O}} $

  Basic electrolyte:

  $ {{\text{2H}}}_{{\text{2}}}{\text{+}}{{\text{4OH}}}^{{\text{-}}}{\text{→}}{{\text{4H}}}_{{\text{2}}}{\text{O +}}{{\text{4e}}}^{{\text{-}}}\;{\text{(HOR)}} $

  $ {{\text{O}}}_{{\text{2}}}{\text{+}}{{\text{2H}}}_{{\text{2}}}{\text{O +}}{{\text{4e}}}^{{\text{-}}}{\text{→}}{{\text{4OH}}}^{{\text{-}}}\;{\text{(ORR)}} $

  Acid electrolyte:

  $ {{\text{H}}}_{{\text{2}}}{\text{→}}{{\text{2H}}}^{{\text{+}}}{\text{+}}{{\text{2e}}}^{{\text{-}}}\;{\text{(HOR)}} $

  $ {{\text{O}}}_{{\text{2}}}{\text{+}}{{\text{4H}}}^{{\text{+}}}{\text{+}}{{\text{4e}}}^{{\text{-}}}{\text{→}}{{\text{2H}}}_{{\text{2}}}{\rm{O\; (ORR)}} $

  Whether in alkaline or acidic electrolytes, the four reactions of H₂/O₂ usually involve multi-step reactions via multiple electrons in the electrocatalysis. Thus, they typically exhibit high kinetic energy barrier due to multi-electron reaction pathways and the large bond energies of H₂O, O₂ and H₂ molecules.^[12] To accelerate the delayed kinetic process of HER, OER, HOR, and ORR, it is necessary to use electrocatalysts, which can improve energy conversion efficiency.^{[13, 14]} So far, precious metals, such as platinum-, iridium- and ruthenium-based catalysts, are still commonly used electrocatalysts.^[15] However, the low crustal abundance of these rare metal electrocatalysts severely limits their commercial applications in energy conversion.^[16] Therefore, there is an urgent need to develop novel electrocatalysts with inexpensive cost and efficient activities for energy conversion.^[17] A common strategy is to introduce supporting materials to maximize the dispersion of precious metals, thereby reducing the use of precious metals while simultaneously increasing the exposed amount when they are utilized as the effective active sites.^{[18, 19]} The resulted precious metal catalysts with low loading can slow down the consumption rate of precious metals.^[20] Another common strategy is to explore non-precious metal materials that are comparable to or exceed the electro-catalytical activities of noble metal-based catalysts as alternatives.^[21] Owing to the abundant reserves and inherent electrocatalytic performance, transition metal-based catalysts have become promising catalysts, such as oxides, phosphates, sulfides or nitrides based on transition metals, etc.^[22] Among them, transition metal nitrides (TMNs) are particularly outstanding because of the characteristic chemical, physical and electronic properties, etc.^[23] In this mini review, the recent basic fundamental studies of TMNs-based materials used in oxygen and hydrogen electrocatalysts are summarized from unitary TMNs, to binary TMNs, ternary TMNs and even polynary TMNs, as well as the electrocatalysts based on TMNs as supporting materials. In unitary TMNs, researchers mainly improve the material and charge transfer capacity and specific surface area of TMNs by means of morphology regulation to further improve the electrocatalytic activities. The electrocatalytic performances of binary TMNs are enhanced by changing the d-electron state of the parent metal and the number of active sites through heteroatomic doping and heterostructure engineering. As a unique structure, the anti-perovskite TMNs are discussed separately because of the ordered element arrangement, stable crystal structure and similar crystal structure to perovskite oxides. Ternary and even polynary TMNs are also substitutes for efficient electrocatalysts due to the enrich d-electron states and variable d-band centers induced by various transition metal elements. In addition, based on the existing TMNS electrocatalysts, the practical application potentials of TMNS as oxygen and hydrogen electrocatalysts are illustrated by examples. Finally, the challenges and prospects of TMNs-based electrocatalyst are discussed.

  TMNs are the interstitial compounds composed of parent metal atoms and nitrogen atoms. The metal atoms are usually arranged in hexagonal close-packed or face centered cubic, while nitrogen atoms with smaller atomic radius are randomly interposed in the gaps of the parent metals.^[24-26] The introduction of nitrogen atoms results in expansion of the original metal lattice and an increase in cell constants. Thus, as the cell constant of the original metal lattice increases, the lattice space between parent metal atoms will also change. Consequently, the interaction between metal and metal atoms weakens, resulting in a corresponding contraction of the d orbitals.^{[23, 24, 27]} This leads to a redistribution of density of states (DOS) near the Fermi level, an increase in the number of valence electrons, and a change in the structure of the compound.^[28] The redistributed DOS can improve catalytic activities of the parent metal and make it have similar catalytic activities to group Ⅷ noble metals (Ru, Rh and Pd).^[28] Such exceptional crystal structures also enable TMNs to own three bonding characteristics: metallic bond, ionic bond, and covalent bond.^[29] Therefore, TMNs simultaneously possess the properties of metal compounds, ionic compounds, and covalent compounds, such as high conductivity, thermal stability, electrochemical durability and corrosion resistance.^[30] TMNs have been widely used in various energy storage/conversion devices, but there is still almost infinite room for performances in practical applications.

  CLASSIFICATION AND APPLICATION OF TMNS

  TMNs-based catalysts are prepared by physical methods, such as plasma, ^[31] vapor deposition^[32] and laser methods.^[33] However, the product varieties of TMNs-based catalysts prepared by physical methods usually have some restrictions, such as CrN and TiN.^[34] However, the morphologies of TMNs prepared by most physical methods are relatively simple. Most of them are thin film structures.^[35] In addition, physical preparation methods are usually complicated and require more demanding conditions, which is not conducive to general synthesis of TMNs.^[35] TMNs-based catalysts can be obtained through chemical methods which usually refer to the nitriding of transition metal oxides, ^[36] transition metal layered double hydroxides (LDH), ^[37] transition metal inorganic salts^[38] and other metal precursors at high temperature (about 300-2000 ℃) and flowing nitrogen (N₂) or ammonia (NH₃) atmosphere.^[28] More specifically, thermal ammonia reduction is usually a gas-solid reaction process which exhibits a mild temperature requirement of about 300-800 ℃.^[39] However, the pyrolysis process in N₂ atmosphere requires a higher temperature, about more than 1200 ℃.^[39] In addition, TMNs can also be prepared by solvent thermal reactions^[40] or thermal decomposition reactions of polymer precursors, ^[41] which usually requires large amounts of nitrogenous compounds, such as small inorganic molecules (such as: urea, melamine, dicyandiamide, etc.)^[42] and organic chemicals.^[43] In short, the preparation of TMNs is a slow solid reaction process.^[25] In addition, the type and number of metal elements, the morphology, the surface structure and the dispersion degree of TMNs will result in different material properties. Therefore, different kinds of TMNs-based materials with different catalytic properties can be prepared by different adjustment strategies, such as changing the type and number of metal elements in TMNs and introducing carriers to form hybrids.

  Unitary TMNs. Unitary TMNs are usually compounds formed from only one transition metal element and nitrogen through a specific arrangement and can usually be expressed as A_xN_y. Unitary TMNs usually show conventional structures, such as hexagonal closed packed, face-centered cubic and simple hexagonal.^[27] The researches of unitary TMNs-based electrocatalysts are mainly focused on the regulations of morphology and coordination. Liao's team^[44] reported the limitations of early-transition-metal nitrides (ETMNs) during electrocatalytic ORR from the perspective of O₂, such as ScN, CrN, VN and TiN. The insufficient d electrons and unsatisfactory surface geometries result in that ScN, TiN, CrN and VN have a certain electrocatalytic oxygen reduction ability. In addition, electrocatalytic performances of ETMN nanoparticles are not excellent enough due to the uncontrollable size, morphology, small surface area and easy agglomeration. Therefore, later researchers improved the electrocatalytic performances of TMNs-based electrocatalysts through the regulation of structures with large specific surface area, such as flower- and nanosheet-like morphologies.^{[45, 46]} Cao et al.^[47] prepared vanadium nitride materials with hollow spherical structure (VN HSs) assembled from porous nanosheets by template-assisted method. Compared with bulk VN, VN HSs showed combined structures composited with microporous and mesoporous, larger specific surface area and uniform mesoporous shell structures. The hollow structure facilitated the shortening of the diffusion pathway between molecules and ions close to the catalytic active site, so that it can exhibit high ORR activity. Xie et al.^[46] also fabricated the emerging Ni₃N nanosheets with 2D morphology that are less than 3 nm. Density functional theory (DFT) calculations confirmed that DOS of Ni₃N nanosheets is significantly higher than that of bulk Ni₃N, indicating better carrier concentration and conductivity of Ni₃N nanosheets, also manifesting that the enhanced electrocatalytic performance could be achieved by limiting Ni₃N aggregation. Benefitting from the disorder structure and improved electrical conductivity, Ni₃N nanosheets substantially improved the OER activity compared to bulk Ni₃N catalyst.

  Abruna et al.^[48] reported the development of a series of TMNs-based catalysts (Figure 1a). Different electronic structures of transition metals led to distinguishing crystal plane structures, such as MnN, VN, CoN, etc. (Figure 1b-d). Therefore, the TMNs based catalysts with different crystal planes exhibit various electrocatalytic ORR activities. Among them, cobalt nitride-based carbon catalyst (Co₃N/C, Figure 1e) shows the most active catalytic activity with half-wave potential of 0.862 V. When Co₃N/C serves for OER, Co₃N is oxidized to Co₃N@CoO_x with the increase of voltage, eventually forming CoO_x completely. At this point, CoO_x acts as active sites during OER. Qiao et al.^[49] synthesized the new type of nickel-based surface unsaturated nitride (Ni-SN@C, Figure 1f-h) by an unsaturated nitriding strategy. Because of the strong complexation of EDTA and relatively high carbonization temperature, Ni-EDTA directly forms the nickel-carbon core-shell structure at 350 ℃ to prevent further nitriding of Ni-SN. Unlike ordinary TMNs, the unsaturated Ni-SN@C does not form a long range ordered nitride lattice or metal-metal nitride heterojunction. The Ni-SN@C combines the high activity of metal-based catalysts and the high stability of nitrides at the same time (Figure 1i). In addition, Zhang et al.^[50] reported free-standing nickel nitride/Ni foam (Ni₃N_1-x/NF) with abundant nitrogen vacancies via N₂ plasma strategy. N vacancies redistribute the charge in nickel nitride, significantly increasing the electron density of Ni atoms near the vacancies and lengthening the distance between the valence band maximum and Fermi level. Thus, Ni₃N_1-x/NF shows excellent HER activity due to the improved adsorption energy for water molecule, the enhanced adsorption-desorption energy of intermediate (*H) and the accelerated kinetic process brought by abundant N vacancies.

  Figure 1

  

  Figure 1.  (a) Schematic illustration, (b-d) XRD patterns and (e) ORR LSV tests in O₂-saturated 1 mol·L^-1 KOH for carbon-supported TMNs (M_xN/C); Copyright 2022, Science. (f) Ni 2p and (g) N 1s XPS spectra for Ni-SN@C; (h) Synchrotron based N K edge and (i) HER LSV tests in 1 mol·L^-1 KOH for Ni-SN@C; Copyright 2021, WILEY-VCH.

  DownLoad: Full-Size Img PowerPoint

  The above work indicates that electrocatalytic abilities of TMNs can be enhanced by changing the morphology to expose more active sites, enhance the transport capacity of electron and material, improve DOS at Fermi level and enhance the carrier concentration and conductivity. Besides, researchers can change the coordination number between metal atoms and nitrogen atoms in TMNs to achieve coordination unsaturation and form metastable phase structure, thus downing the reaction energy barrier of TMNs in electrocatalytic reactions and enhancing the catalytic activities.

  Binary TMNs. The electrochemical activities of unitary TMNs are sometimes difficult to exceed that of platinum-based catalysts.^{[51, 52]} Therefore, researchers also typically combine two different transition metals with nitrogen atoms to form binary TMNs. Binary TMNs are mainly focused on TMNs-based heterojunction structure formed by interface coupling and metal atom-doped TMNs. The strategy of metal atomic doping is mainly based on changing the d-electron state of the parent metal nitride through the regulation of electronic structure, then adjusting the gap between the d-band center and Fermi level, and then changing the electrochemical properties of the parent nitride, so as to improve the electrocatalytic activities.^{[24, 25, 52, 53]} He et al.^[54] designed Co and N co-doped VN (VCoN) nanoplates as ORR/HER electrocatalysts with a one-pot synthetic route. Compared with the pure-phase VN, VCoN nanoplates exhibit a larger specific surface area and possess a higher density of active centers, which guarantee larger contact area between the reactants and VCoN nanoplates, thus achieving enhanced activities. Liao et al.^[44] took VN to propose the strategy of enriching d electrons by doping 3d transition metal to enhance ORR activity. As d orbitals of different transition metal atoms are in different electron-filled states, such as fully filled state, half-filled state, and so on, the ability of acquiring electrons for N atoms is different (Figure 2a). Three electrons transported from the half-filled d orbital of Co atoms to N can lead to significant enrichment of d electrons on the V atom (Figure 2b). This is relatively easier compared to Cu atoms with a fully filled d orbital or Cr atoms with a half-filled d orbital. Compared with other VN based catalysts, the Co doped VN catalyst shows the best performance (Figure 2c-d). Similarly, Liao et al.^[45] also further synthesized hierarchically 3D VCoN micro flowers (VCoN MFs, Figure 2e-g) by the template-free solvent-thermal strategy. The VCoN MFs display high transfer rate of electroactive substances and high utilization rate of active sites. The authors confirmed that ETMNs with d electron deficiency can be promising ORR catalysts by d electron enrichment strategy with d electron-rich doping elements.^[54] Luo et al.^[55] designed the niobium nitride (NbN) nanogrid through nitriding Nb complexes in NH₃ flow. The author proposes that doping the second transition metal (Co) to NbN significantly improves the ORR activity of NbN. The doped Co changes the lattice parameters of NbN and the original coordination environment, thus changing the ORR performance. Luo et al.^[56] also reported Cr-doped cobalt nitride nanorod array (Cr-Co₄N) as the high-efficiency HER performance. The charge of Cr₄ (+0.717) in Cr-Co₄N is significantly higher than that of Co₄ (+0.211) in Co₄N, indicating that Cr as the doped heteroatoms exhibits a higher positive valence and captures oxygen atoms and further adsorbed H₂O molecules through strong electrostatic attraction. Furthermore, the doped Cr changed electronic structures of pure-phase Co₄N cause d-band center of cobalt atoms to move away from the Fermi level. As a result, the binding interaction between adsorbates and Cr-Co₄N catalysts is weakened, thus enhancing HER activity. In addition, the active sites formed by doping offer more possibilities, which is probably one of the reasons for enhanced activity of the doped cobalt nitride catalyst compared to traditional materials.^[57-59]

  Figure 2

  

  Figure 2.  (a) N-determined competitive mechanism; (b) Electron-transfer model of V_0.95Co_0.05Ns for ORR activity; ORR LSV tests in 0.1 mol·L^-1 (c) HClO₄ and (d) KOH for VN and V_0.95M_0.05Ns catalysts; Copyright 2016, American Chemical Society. (e) Schematic illustration, (f) electron-transfer model for ORR activity and (g) ORR LSV tests in 0.1 mol·L^-1 KOH of V_0.95Co_0.05N MFs; Copyright 2018, American Chemical Society. (h) HR-TEM image, (i) XRD pattern, (j) electrocatalytic HER performance and (k) calculated adsorption energy for H₂O of Ni₃N-VN/NF; Copyright 2019, WILEY-VCH.

  DownLoad: Full-Size Img PowerPoint

  To sum up, the doping of the second metals can indeed change the d electron state of the metal atom in parent TMNs. The second transition metal with more d electrons which are not in the fully-filled state or cannot easily become fully-filled or semi-filled state after gaining or losing electrons is more conducive to enrich d electrons for the metal atoms of the parent TMNs. This can effectively change the chemical valence state of metal atoms, shorten, or increase the distance between d-band center and Fermi level, thus improving the electrostatic attraction of TMNs to adsorb species. The doping of the second metals can also change the lattice constant of the parent TMNs and the original coordination environment of metal atoms. All these are effective strategies to improve electrocatalytic activities of TMNs.

  Recently, the heterojunction construction can also perfect the selectivity, activity, and stability of TMNs-based materials.^{[60, 61]} The interface coupling phenomenon in the heterojunction structure can lead to lattice distortion and create more active sites through the reconstruction of electronic structure on the parent nitride surface, improving the adsorption capacity of the adsorbent and enhancing the electrocatalytic activities. The heterogeneous interface not only provides more favorable sites for the adsorption/activation of active substances, but also significantly promotes the charge transfer and plays a very high protective role in the exposed active sites.^[62] Heterojunction structures formed by TMNs and different kinds of substances will generate heterogeneous interfaces with different chemical properties, and therefore exhibit different catalytic activities. Fu et al.^[62] developed Ni-V-based nitride heterojunctions anchored by nickel foam as HER catalyst (Ni₃N-VN/NF, Figure 2h-j). DOS of the Ni₃N-VN heterojunction at Fermi level is significantly higher than that of VN and Ni₃N, indicating that the Ni₃N-VN/NF can improve electron mobility and accelerate electron transport. The adsorption capacity (Figure 2k) of the Ni₃N-VN/NF for H₂O is also about twice that of Pt, ensuring the effective adsorption of water on the heterogeneous interface of Ni₃N-VN and providing conditions for subsequent generation of H* and H₂. Ni₃N-VN heterostructure was prepared based on nickel foam, not only achieving the morphology and pore structure regulation of Ni₃N-VN, but also improving the conductivity of Ni₃N-VN/NF catalyst. Rao et al.^[63] also reported interfacial catalytic materials of Ni and Co₂N (Ni/Co₂N) for bi-functional hydrogen (HER/HOR) catalysts. The formation of Ni and Co₂N interface structure leads to interfacial charge transfer. Thus, the N and Co sites at the Ni/Co₂N catalyst interface is more conducive to adsorbing hydrogen.

  Similarly, Lei et al.^[64] also synthesized the N-doped carbon @cobalt-copper nitrides/copper foam nanoarrays (NC@CoN/Cu₃N/CF) with hollow tubular morphology. The NC@CoN/Cu₃N/CF shows fast OER/HER reaction kinetics thanks to highly exposed active sites, abundant "highway" for electron transport, enhanced conductivity, and synergies between cobalt-copper nitrides and copper foam. In addition, Fu et al.^[65] also reported the three-dimensional hierarchical structure with vanadium-nickel-based nitride heterojunctions supported on carbon cloth as the self-standing HER catalyst (VN@Ni₃N-Ni/CC) for water electrolysis. The VN@ Ni₃N-Ni/CC hybrids exhibit improved electrolyte diffusion, accelerated gas release rate, and increased reactive plane exposure densities.

  Whether for nickel foam, copper foam, carbon cloth, or other types of support materials, they show a number of advantages over powdered catalysts in conventional electrocatalytic reactions. This is because: (1) In electrocatalytic reactions, the conventional powder catalysts are inevitably used in conjunction with the adhesives (such as Nafion) to load onto the electrode surface; (2) Al-though the actual usage number of adhesives is very small, the usage of binder, to a certain extent, will impede the contact between electrolyte and TMNs-based catalyst, thus reducing the catalytic activities and possibly increasing the over-potential of catalytic reaction; ^[66] (3) The different surface properties of various TMNs-based catalysts lead perhaps to the difference of usage effect between catalysts and adhesives. In electrocatalytic reactions, the powdery catalysts also probably fall off from the electrode surface, causing poor catalytic activities.^[67] In addition, the general price of adhesives is expensive, but also shows a certain toxicity.^[68] Thus, to further improve the application effect of TMNs-based catalysts, researchers have also reported a variety of self-supporting TMNs-based catalysts, such as MXene (the definition: layered 2D metal carbides/carbonitrides), ^[68] nickel foam, ^[62] copperfoam, ^[64] carbon fiber/carbon paper^[65] and other supporting substrate materials with good structural/chemical stability and high electrical conductivity. The self-supporting TMNs-based materials can avoid the preparation of working electrode during the testing process, which avoids the use of binder and dispersant, and improves the catalytical efficiency. In addition, in practical applications, such as fuel cells and metal-air cells, the use of collector layer can also be eliminated, thus improving the efficiency of practical applications.

  Anti-perovskite TMNs. As a kind of unique nitride, anti-perovskite TMNs possess similar crystal structure with perovskite oxides. Anti-perovskite TMNs exhibit orderly element arrangement, stable crystal structure and high flexibility in composition. The general formula of anti-perovskite TMN is ANM₃, where A is the bivalent or trivalent metal element, and M is the transition metal element.^[43] Anti-perovskite TMNs are usually the Pm-3m type face-centered cubic crystal structure.^[69-72] In theory, each element is orderly arranged. The crystal structure is also stable. Through flexible replacement of A or M elements, electrocatalytic performances of anti-perovskite TMNs-based materials are effectively regulated.^[73] Such materials with rich physical properties like giant magneto-resistance, superconductivity, negative thermal expansion and constant resistivity have already been widely reported, but there are still few studies in the field of electrocatalysis.^[72-74]

  As the unique anti-perovskite TMNs, Co₄N exhibits excellent conducting electricity and intrinsic activity for electrocatalytic reactions. Li et al.^[53] reported Co₄N nanoparticles anchored on porous carbon (CoN_x/Zn-NC, Figure 3a-c) with dual-active-sites through the self-polymerization method of biomass energy and coupling of nitrogen-rich species with metallic ions. Guo et al.^[74] designed and successfully synthesized two-dimensional metallic Co₃FeN nanosheets with porous structures. Due to the synergistic effect of bimetal and the complete exposure of atoms on the side surface and the edge of pore region, the exposed surface has the lowest OH adsorption energy, thus showing enhanced catalytic performance. At the same time, the porous structure can not only accelerate electron transport through the highly oriented crystal structure of metal state, but also facilitate the diffusion of inter-mediates and gases. The enriched two-dimensional hole Co₃FeN nanosheets enhance the catalytic activity. Moreover, Xu et al.^[75] also reported Ni₃FeN-based nitrogen-doped graphene electrocatalyst (Zn-Ni₃FeN/NG, Figure 3d). The introduction of larger Zn atoms changes the lattice parameters of original Ni₃FeN. The resulting stress also changes the electronic structure of Ni₃FeN, thus optimizing the adsorption and desorption capacity of oxygen and corresponding intermediates on the Zn-Ni₃FeN/NG catalyst surface. The Zn-Ni₃FeN/NG thus displays excellent bifunctional ORR/OER activities, where the overvoltage difference is about 0.74 V (Figure 3e-f). Yang et al.^[76] has also prepared the Ni₃FeN catalyst supported on carbon substrate (Ni₃FeN/r-GO-20, Figure 3g) using alginate fibers and rGO via the green and economical method. The bimetallic synergies between metallic Ni and Fe atoms enhance the metallic conductivity of Ni₃FeN. The metal properties and unique core-shell structure of Ni₃FeN also provide more active sites. The coordination between metal and N atoms also promotes electron transfer from the surface of Ni₃FeN cluster to carbon substrate, which not only regulates the surface electronic structure of Ni₃FeN, but also improves the electrocatalytic OER/HER activities of Ni₃FeN/r-GO-20 (Figure 3g-i).

  Figure 3

  

  Figure 3.  (a) HR-TEM image, (b) XRD pattern and (c) ORR LSV tests in 0.1 mol·L^-1 KOH solution of CoN_x/Zn-NC; Copyright 2019, Elsevier. (d) XRD pattern, (e) ORR LSV curves and (f) OER LSV curves in 0.1 mol·L^-1 KOH for Zn-Ni₃FeN/NG; Copyright 2021, Royal Society of Chemistry. (g) HR-TEM image, (h) OER and (i) HER LSV curves in 1.0 mol·L^-1 KOH for Ni₃FeN/r-GO-20; Copyright 2018, American Chemical Society.

  DownLoad: Full-Size Img PowerPoint

  The synergistic effect between metal atoms in anti-perovskite TMNs benefits to improve metallic properties and electrical conductivity. By introducing heteroatoms, the stress effects are generated in anti-perovskite TMNs. And the original electron configuration is changed. Thus, the adsorption and desorption capacity of oxygen-bearing species is promoted on the antiperovskite TMNs surface. The electron transfer effect can also be produced at the interface of the anti-perovskite TMNs with carbon substrate, thus improving the catalytic performances. However, the surfaces of TMNs are easily oxidized into corresponding hydroxides or oxides, hindering the contact between electrolytes and active sites, decreasing the charge transfer efficiency, and thus resulting in reduced catalytic activities.^[77] Exploring modification strategies for TMNs to enhance their electrical conductivity remains limited, which mostly leads to high overpotential in long running states and unstable catalytic reactions in strong alkaline media.^[77] Therefore, TMNs can be utilized as the catalytic active species to combine with carbon material to form the composite catalyst. Currently, common strategies include introducing carbon support nanomaterials with strong electrical conductivity to form TMNs/carbon composite structures. Carbon support nanomaterials not only protect TMNs from spontaneous aggregation, but also prevent them from accumulating under high temperatures, thereby minimizing the size of TMNs, and maximizing the exposure density of the optimal active sites.^[51] Besides, the doping of heteroatoms into carbon nanomaterials with different electronegativity (χ, the χ of carbon is 2.55), such as more electronegative nitrogen atoms (χ = 3.04), can change the original orbital hybridization state of carbon nanomaterials and the density of electron cloud. The doped nitrogen not only endows carbon nanomaterials more defects, but also regulates the electron distribution state of surrounding carbon atoms.^[78] The combination catalysts of TMNs with carbon nanomaterials can also promote the transfer of charge and oxygen by increasing oxygen pathways, providing more active sites, such as quaternion N with electron donor properties to promote ORR activity, and pyridine N with electron acceptor properties to enhance OER activity.^[79] The synergistic effect between TMNs and carbon nanomaterials is also conducive to improving the electro-catalytic performance of TMNs/carbon composite structures.^[80] At present, numerous researchers have designed highly efficient and stable electrocatalytic O₂/H₂ catalysts by such means. For example, Cheng et al.^[81] designed Co₄N nanoparticles/nitrogen-doped carbon frameworks (Co₄N@NC, Figure 4a-c) hybrids for OER/HER via interfacial engineering strategy. In Figure 6c, Co₄N@NC exhibits higher DOS than Co₄N and NC, indicating significantly increased carrier density during OER/HER charge transfer. The NC, the authors point out, not only facilitates charge transfer, but also provides more active centers. Besides, NC also avoids the surface oxidation of Co₄N, thus preventing a large charge transfer resistance between Co₄N and NC. Synergistic effects between Co₄N and NC also benefit OER/HER. Chen et al.^[82] also took Co₄N as the main active site and then effectively regulated the diameter and dispersion degree of morphology of Co₄N nanocrystalline via melamine, thus improving the utilization rate and inherent activity of Co₄N nanocrystalline. The conductivity and electrochemical surface area of Co₄N are further improved by combining Co₄N nanocrystals with N-doped carbon substrate (Co₄N@NC-m, Figure 4d). The electrocatalytic ORR/OER activities of Co₄N@NC-m are higher than that of Pt/C and IrO₂ (Figure 4e-f). In addition, the electrochemical stability of Co₄N@NC-m is effectively enhanced by the protection of N-doped carbon substrate against Co₄N nanocrystals. Xu et al.^{[83, 84]} reported anti-perovskite Ni₄N/VN and Ni₃FeN/VN heterostructures anchored on nitrogen-doped graphene with excellent bifunctional catalytic activity and stability due to the electronic coupling between the two components.

  Figure 4

  

  Figure 4.  (a) XRD patterns and (b) side view of Co₄N@NC model system (The yellow, gray, and green balls are presented in Co, C and N atoms, respectively.), (c) DOS of Co₄N@NC Co₄N and NC; Copyright 2020, American Chemical Society. (d) XRD pattern, (e) ORR LSV test and (f) OER LSV test 0.1 mol·L^-1 KOH for Co₄N@NC-m; Copyright 2019, Elsevier.

  DownLoad: Full-Size Img PowerPoint

  Ternary Even Polynary TMNs. There are more kinds of metal atoms in ternary even polynary TMNs, which probably lead to the more favorable stress effect in TMNs. Electronic rearrangement is potentially more pronounced. More kinds of transition metals are possibly more conducive to improving electrical conductivity of TMNs and providing more possible active sites for different electrocatalytic reactions, thus enabling TMNs-based catalysts to achieve various electrocatalytic reactions. A highly efficient and durable OER electrocatalyst, CuNCo_3-xV_x (0≤x≤1), ^[85] was prepared by partially substituting the Co site with V of anti-perovskite CuNCo₃ (Figure 5a). The synthesized CuNCo_2.4V_0.6 catalyst reaches a current density of 10 mA·cm^-2 with only 235 mV overpotential. DOS calculations show that Co is partially replaced by V atoms, getting a negative shift of the d-band center near the Fermi level of CuNCo₃. This can weaken the interaction between adsorbents and CuNCo_2.4V_0.6, further promoting OER performance (Figure 5b). This V replaced Co-based TMN catalyst provides a novel designing electrocatalyst with ideal activities. A class of nickel-based TMN, Cu_xIn_1-xNNi₃ (0≤x≤1), ^[71] with good electrical conductivity is also developed by taking advantage of the controllable composition of TMNs (Figure 5c). A series of Cu_xIn_1-xNNi₃ were synthesized by partial substitution of A sites in ANNi₃ (A = Cu or In) by Cu or In. The structures of Pm-3m TMNs are main-tained before and after elemental substitution. However, the lattice constant of ANNi₃ (A = Cu or In) is changed due to the difference of atomic radii between Cu and In before and after elemental substitution. The partially replaced material, Cu_0.4In_0.6NNi₃, displays better HER activity than unreplaced CuNNi₃ and InNNi₃ catalysts (Figure 5d). The high-entropy metal nitride (HEMN-1, Figure 5e) is also reported by a soft urea template method combined with the mechanical ball milling.^[86] The HEMN-1 exhibits typical cubic crystal structure and contains a variety of metallic components (V, Cr, Nb, Mo, Zr, Figure 5f). This is a new method for the preparation of high-entropy metal nitrides that can extend to other metal components or more metal components. The above doping strategy optimizes the electrocatalytic activities of TMNs. The component regulation provides an effective design idea for the development of other ternary even polynary TMNs-based catalysts. The application can be extended to a wider field of electrocatalysis.

  Figure 5

  

  Figure 5.  (a) Unit cell models and (b) OER LSV tests in 1.0 mol·L^-1 KOH of CuNCo₃ and CuNCo_3-xV_x; Copyright 2019, American Chemical Society. (c) 2×2 unit cell models and (d) HER LSV tests in 1.0 mol·L^-1 KOH of InNNi₃ and Cu_0.5In_0.5NNi; Copyright 2019, American Chemical Society. (e) Schematic illustration and (f) EDS elemental maps of HEMN-1; Copyright 2018, WILEY-VCH.

  DownLoad: Full-Size Img PowerPoint

  TMNs as Substrate. The different components of TMNs show different catalytic activities, which can be improved by optimizing strategies such as the regulation of metal elements. However, compared with commercial precious metal catalysts, there is still a certain distance. Using TMNs as supporting materials to disperse precious metals can not only significantly improve catalytic activities of TMNs, but also is expected to reduce the consumption rate of precious metals.^{[76, 87]} In addition, the combination of TMNs and noble metal species can also provide multiple active sites, so that designed catalysts can achieve the purpose of multi-functional catalytic activities. Goodenough et al.^[69] designed ordered Fe₃Pt alloys supported by the porous Ni₃FeN substrate (Fe₃Pt/Ni₃FeN, Figure 6a). For Fe₃Pt/Ni₃FeN hybrids, Fe₃Pt and Ni₃FeN mainly contribute respectively to ORR activity and OER performance (Figure 6b-c). To minimize the usage of Pt, Wang et al.^[88] also designed the PtNiN core-shell structure (PtNiN) for ORR, in which low-content Pt is loaded on the inexpensive NiN core in the form of shell (Figure 6d-e). Nitrogen atom and core-shell structure improve the ORR performance of Pt and provide stability to inhibit dissolution under high oxidation cycle conditions (Figure 6f). The 3D TiN-based nanostructures are also utilized as the support to Pt as ORR catalysts (Pt/3D TiN, Figure 6g-h).^[89] The resulting Pt/3D TiN exhibits superior activities to Pt/C (Figure 6i). The above work manifests that TMNs as the support to load precious metals can not only make precious metals highly dispersed, but also improve the utilization efficiency of precious metals. The high conductivity of TMNs can also be combined with the high intrinsic electrocatalytic performances of precious metals. The resulting TMNs-based catalytic materials generally possess better activities than commercial Pt/C in both acidic and alkaline electrolytes.

  Figure 6

  

  Figure 6.  (a) XRD patterns, (b) ORR and (c) OER LSV test in 0.1 mol·L^-1 KOH of Fe₃Pt/Ni₃FeN and Ni₃FeN; Copyright 2017, Wiley-VCH. (d) XRD pattern, (e) HAADF image and (f) ORR LSV test in 0.1 mol·L^-1 HClO₄ of PtNiN/C; Copyright 2012, American Chemical Society. (g-h) TEM images and (i) ORR LSV test in 0.1 mol·L^-1 HClO₄ of Pt/3D TiN; Copyright 2019, Wiley-VCH.

  DownLoad: Full-Size Img PowerPoint

  Applications of TMNs. Due to excellent electrocatalytic oxygen/hydrogen reaction activities, practical application prospects of TMNs-based materials in energy devices are often explored through assembling metal-air batteries, fuel cells and water splitting devices. Lai et al.^[90] controllably synthesized the CoN₃ nanoparticles/N-doped graphite carbon (CoN₃@NC-7-1000, Figure 7a) with the main exposed crystal surface of (220) via annealing Co/Zn-ZIF-67. Due to stable ORR performance in 0.5 M H₂SO₄ (the half-wave potential of 0.72 V and the high current density retention of 91%), the CoN₃@NC-7-1000 is assembled for hydrogen/oxygen (H₂/O₂) and hydrogen/air (H₂/air) fuel cells to evaluate practical application potential (Figure 7b-c). TMNs are also widely utilized in other metal-air or metal-oxygen batteries. For example, Choi et al.^[91] have synthesized a mesoporous titanium nitride (mesoporous TiN) material with two-dimensional hexagonal structure for Li-O₂ batteries. Excellent electrical conductivity and pore structures make excellent reversibility for the mesoporous TiN-based Li-O₂ battery. Yao et al.^[76] constructed Ni₃FeN embedded reduced graphene oxide (Ni₃FeN/r-GO, Figure 7d) for OER/HER. Benefitting from the high electrical conductivity and fast electronic transport channels of r-GO, the overpotentials of Ni₃FeN/R-GO catalyzed OER and HER are only 270 and 94 mV, respectively (Figure 7e). The overall water splitting is constructed with Ni₃FeN/R-GO catalysts and possessed superior durability (Figure 7f). Zou et al.^[92] prepared amorphous cobalt nitride coupled with nitrogen-doped graphene (CoN_x/NGA) as superior ORR/OER/HER catalysts. The CoN_x/NGA not only drives the zinc-air battery or the water splitting electrolyzer independently, but also integrates the two together to form a self-driven water splitting electrolyzer powered by the zinc-air battery. A hybrid structure of cobalt nitride nanosheets array grown on nickel foam and coupled with N-doped carbon (CoN@NC) was synthesized and reported.^[93] The coupling effect between cobalt nitride and N-doped carbon and the hierarchical porous structure of CoN@NC promoted the mass/electron transport. Thus, the CoN@NC shows enhanced ORR/OER/HER activities. In addition, the CoN@NC displays excellent activity and stability in flexible zinc-air batteries.

  Figure 7

  

  Figure 7.  (a) XRD pattern of CoN₃@NC-7-1000, (b) H₂/O₂ and H₂/air fuel cell performances for CoN₃@NC-7-1000, (c) the durability tests of H₂/air fuel cells based on CoN₃@NC-7-1000 catalyst; Copyright 2019, Royal Society of Chemistry. (d) HR-TEM image and (e) HER/OER curves of Ni₃FeN/r-GO-20, (f) the stability test of time-current density for Ni₃FeN/r-GO-20 in a two-electrode configuration at 1.60 V; Copyright 2017, American Chemical Society.

  DownLoad: Full-Size Img PowerPoint

  CONCLUSION AND OUTLOOK

  As emerging non-noble metal materials, TMNs and corresponding hybrids are outstanding among numerous electrocatalytic materials (such as transition metal alloys-, oxides-, phosphate-based materials, etc.) due to the low resistivity and excellent chemical stability. TMNs not only exhibit combined properties of covalent compounds, ionic compounds, and metal compounds, but also possess electrocatalytic activities like that of group Ⅷ noble metals (Ru, Rh and Pd) due to unique electronic structures of interstitial compounds. In this mini review, TMNs with different metal contents and types are reviewed, such as unitary, binary, ternary and even polynary TMNs and anti-perovskite TMNs. The improvement strategies of electrocatalytic performances commonly used for each type of TMNs are summarized with examples. The catalysts with TMNs as the support dispersed noble metal, other TMNs-based hybrids as electrocatalytic materials, and practical applications in electrocatalytic H₂/O₂ reactions are also reviewed. And the practical applications in H₂/O₂ fuel cells, water splitting electrolyzer and zinc-air batteries are also discussed. Through the above discussion, an efficient and stable electrocatalyst must possess the advantages of suitable electronic structure, low resistivity, exposed active sites as many as possible, and abundant gas/electron transport pathways. However, in this review, the design and construction of TMNs-based materials and the practical application still have some expansion room. Here, we put forward the following discussions on the possible shortcomings of TMNs-based materials:

  Synthesis. At present, most synthesis strategies of TMNs-based materials are still achieved through the nitridation of transition metal precursors at high temperature under the condition of N₂ or NH₃. They often increase the preparation cost and make the synthesis pathways more complex and tedious. Therefore, it is necessary to find a simpler, more economical and environmentally friendly synthesis technology. In addition to the modification strategies reviewed in this review, researchers can also devote to controlling the catalytic selectivity by precisely controlling the exposed crystal surface of TMNs to achieve more efficient catalytic performances. In oxidation reactions, TMNs are usually converted into oxides or hydroxyl oxides at high voltage. Thereby, TMNs can also be utilized as pre-catalysts for in-situ transformation into nitride-core or oxide-shell structure under high potential according to reaction conditions. This is probably more conducive to specific environments of electrocatalytic OER. Meanwhile, advantages of TMNs are also combined with those of oxides. Thus, multi-functional electrocatalytic process is easily realized.

  Stability. The catalytic reactions include electrocatalytic hydrogen reaction (HER/HOR) and oxygen reaction (OER/ORR) in this review, and they usually need to be carried out in acidic or alkaline aqueous solutions. However, the stability of metal nitrides in aqueous solutions is usually not ideal, which perhaps polarizes the surface of TMNs-based materials under certain pH conditions. Thereafter, the corrosion resistance of TMNs-based materials to the electrolyte should also be paid attention for enhancing the catalytic stability of TMNs-based materials. This requires researchers to explore more types of substrates with excellent electrical conductivity and abundant electron transport channels for depositing or loading TMNs species, improving the stability. Moreover, TMNs are easily oxidized at high potential. Thus, to maintain the chemical structure and stability, researchers can also build a passivation layer on the surface of TMNs to protect it from being oxidized at high voltage during OER process.

  Mechanism. The thorough understanding of catalytic mechanism during electrocatalytic reactions is crucial to constructing efficient and stable TMNs-based materials. The adsorption and desorption processes between TMNs-based materials and reactants, reaction intermediates and electrolytes are usually complex when catalytic reactions take place. In addition, the electrochemical reaction process of TMNs-based materials still lacks detailed research reports. Therefore, researchers can consider strengthening in-situ characterization techniques on TMNs-based materials during HER/HOR and OER/ORR, such as in-situ Raman technology, in-situ infrared spectroscopy and in-situ transmission electron microscopy so as to further understand whether the phase or chemical composition of TMNs-based materials changes during catalytic reactions to facilitate the construction of TMNs-based electrocatalysts.

  
  ACKNOWLEDGEMENTS: This work is supported by the Natural Science Foundation of Jiangsu Province (No. BK20191430), Six Talent Peaks Project in Jiangsu Province (No. XNY-009), High-tech Research Key Laboratory of Zhenjiang (No. SS2018002), Jiangsu Province Key Laboratory of Intelligent Building Energy Efficiency (No. BEE201904) and a Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions. The authors declare no competing interests.
  COMPETING INTERESTS
  ADDITIONAL INFORMATION
  For submission: https://mc03.manuscriptcentral.com/cjsc
  Full paper can be accessed via http://manu30.magtech.com.cn/jghx/EN/10.14102/j.cnki.0254-5861.2022-0036
  
• 1. [1]

     Gao, C. B.; Lyu, F. L.; Yin, Y. D. Encapsulated metal nanoparticles for catalysis. Chem. Rev. 2021, 121, 2, 834-881.

  2. [2]

     Zhang, J. Q.; Shang, X.; Ren, H.; Chi, J. Q.; Dong, B.; Liu, C. G.; Chai, Y. M. Modulation of inverse spinel Fe₃O₄ by phosphorus doping as an industrially promising electrocatalyst for hydrogen evolution. Adv. Mater. 2019, 31, 1905107. doi: 10.1002/adma.201905107

  3. [3]

     Tian, Y. H.; Liu, X. Z.; Xu, L.; Yuan, D.; Dou, Y. H.; Qiu, J. X.; Li, H. N.; Ma, J. M.; Wang, Y.; Su, D.; Zhang, S. Q. Engineering crystallinity and oxygen vacancies of Co(Ⅱ) oxide nanosheets for high performance and robust rechargeable Zn-air batteries. Adv. Funct. Mater. 2021, 2101239.

  4. [4]

     Dong, B.; Xie, J. Y.; Wang, N.; Gao, W. K.; Ma, Yu.; Chen, T. S.; Yan, X. T.; Li, Q. Z.; Zhou, Y. L.; Chai, Y. M. Zinc ion induced three-dimensional Co₉S₈ nano-neuron network for efficient hydrogen evolution. Renew. Energ. 2020, 157, 415-423. doi: 10.1016/j.renene.2020.05.057

  5. [5]

     Wang, Z. L.; Liu, W. J.; Hu, Y. M.; Guan, M. L.; Xu, L.; Li, H. P.; Bao, J.; Li, H. M. Cr-doped CoFe layered double hydroxides: highly efficient and robust bifunctional electrocatalyst for the oxidation of water and urea. Appl. Catal. B 2020, 272, 118959. doi: 10.1016/j.apcatb.2020.118959

  6. [6]

     Tian, Y. H.; Xu, L.; Li, M.; Yuan, D.; Liu, X. H.; Qian, J. C.; Dou, Y. H.; Qiu, J. X.; Zhang, S. Q. Heterostructure CoS/CoO double active centers supported on N-doped graphene: interface engineering for bifunctional oxygen catalysis in rechargeable Zn-air batteries. Nano-Micro. Lett. 2021, 13, 3. doi: 10.1007/s40820-020-00526-x

  7. [7]

     Zhang, W.; Lai, W. Z.; Cao, R. Energy-related small molecule activation reactions: oxygen reduction and hydrogen and oxygen evolution reactions catalyzed by porphyrin- and corrole-based systems. Chem. Rev. 2017, 117, 3717-3797. doi: 10.1021/acs.chemrev.6b00299

  8. [8]

     Zhang, B. Q.; Wang, S. Y.; Fan, W. J.; Ma, W. G.; Liang, Z. X.; Shi, J. Y.; Liao, S. J.; Li, C. Photoassisted oxygen reduction reaction in H₂-O₂ fuel cells. Angew. Chem. Int. Ed. 2016, 55, 14748-14751. doi: 10.1002/anie.201607118

  9. [9]

     Fan, R. Y.; Zhou, Y. N.; Li, M. X.; Xie, J. Y.; Yu, W. L.; Chi, J. Q.; Wang, L.; Yu, J. F.; Chai, Y. M.; Dong, B. In situ construction of Fe(Co)OOH through ultra-fast electrochemical activation as real catalytic species for enhanced water oxidation. Chem. Eng. J. 2021, 426, 131943. doi: 10.1016/j.cej.2021.131943

  10. [10]

      Fan, R. Y.; Xie, J. Y.; Liu, H. J.; Wang, H. Y.; Li, M. X.; Yu, L.; Luan, R. N.; Chai, Y. M.; Dong, B. Directional regulating dynamic equilibrium to continuously update electrocatalytic interface for oxygen evolution reaction. Chem. Eng. J. 2022, 431, 134040. doi: 10.1016/j.cej.2021.134040

  11. [11]

      Jiang, H.; Gu, J. X.; Zheng, X. S.; Liu, M.; Qiu, X. Q.; Wang, L. B.; Li, W. Z.; Chen, Z. F.; Ji, X. B.; Li, J. Defect-rich and ultrathin N doped carbon nanosheets as advanced trifunctional metal-free electrocatalysts for the ORR, OER and HER. Energy Environ. Sci. 2019, 12, 322-333. doi: 10.1039/C8EE03276A

  12. [12]

      Puerto, A. P.; Ng, K. L.; Fahy, K.; Goode, A. E.; Ryan, M. P.; Kucernak, A. Supported transition metal phosphides: activity survey for HER, ORR, OER, and corrosion resistance in acid and alkaline electrolytes. ACS Catal. 2019, 9, 11515-11529. doi: 10.1021/acscatal.9b03359

  13. [13]

      Wang, Z. L.; Bao, J.; Liu, W. J.; Xu, L.; Hu, Y. M.; Guan, M. L.; Zhou, M.; Li, H. M. Strong electronic coupled FeNi₃/Fe₂(MoO4)₃ nanohybrids for enhancing the electrocatalytic activity for the oxygen evolution reaction. Inorg. Chem. Front. 2020, 7, 2791-2798. doi: 10.1039/D0QI00525H

  14. [14]

      Xu, L.; Wang, C.; Deng, D. J.; Tian, Y. H.; He, X. Y.; Lu, G. F.; Qian, J. C.; Yuan, S. Q.; Li, H. N. Cobalt oxide nanoparticles/nitrogen-doping graphene as the highly efficient oxygen reduction electrocatalyst for rechargeable zinc-air batteries. ACS Sustain. Chem. Eng. 2019, 8, 343-350.

  15. [15]

      Deng, D. J.; Tian, Y. H.; Li, H. P.; Li, H. N.; Xu, L.; Qian, J. C.; Li, H. M.; Zhang, Q. Electrospun Fe, N co-doped porous carbon nanofibers with Fe₄N species as a highly efficient oxygen reduction catalyst for rechargeable zinc-air batteries. Appl. Surf. Sci. 2019, 492, 417-425. doi: 10.1016/j.apsusc.2019.06.237

  16. [16]

      Wang, Z. L.; Liu, W. J.; Hu, Y. M.; Xu, L.; Guan, M. L.; Qiu, J. X.; Huang, Y. P.; Bao, J.; Li, H. M. An Fe-doped NiV LDH ultrathin nanosheet as a highly efficient electrocatalyst for efficient water oxidation. Inorg. Chem. Front. 2019, 6, 1890-1896. doi: 10.1039/C9QI00404A

  17. [17]

      Wei, C.; Rao, R. R.; Peng, J. Y.; Huang, B. T.; Stephens, I. E. L.; Risch, M.; Xu, Z. C.; Shao, H. Y. Recommended practices and benchmark activity for hydrogen and oxygen electrocatalysis in water splitting and fuel cells. Adv. Mater. 2019, 31, 1806296. doi: 10.1002/adma.201806296

  18. [18]

      Varela, A. S.; Ju, W.; Strasser, P. Molecular nitrogen-carbon catalysts, solid metal organic framework catalysts, and solid metal/nitrogen-doped carbon (MNC) catalysts for the electrochemical CO₂ reduction. Adv. Energy Mater. 2018, 1703614.

  19. [19]

      Liu, L. C.; Corma, A. Metal catalysts for heterogeneous catalysis: from single atoms to nanoclusters and nanoparticles. Chem. Rev. 2018, 118, 4981-5079. doi: 10.1021/acs.chemrev.7b00776

  20. [20]

      Gewirth, A. A.; Varnell, J. A.; DiAscro, A. M. Nonprecious metal catalysts for oxygen reduction in heterogeneous aqueous systems. Chem. Rev. 2018, 118, 2313-2339. doi: 10.1021/acs.chemrev.7b00335

  21. [21]

      Chen, X. C.; Zhou, Z.; Karahan, H. E.; Shao, Q.; Wei, L.; Chen, Y.; Recent advances in materials and design of electrochemically recharge-able zinc-air batteries. Small 2018, 1801929.

  22. [22]

      Borghei, M.; Lehtonen, J.; Liu, L.; Rojas, O. J. Advanced biomass-derived electrocatalysts for the oxygen reduction reaction. Adv. Mater. 2018, 30, 1703691. doi: 10.1002/adma.201703691

  23. [23]

      Zheng, J. F.; Zhang, W. F.; Zhang, J. X.; Lv, M. Y.; Li, S. L.; Song, H. Y.; Cui, Z. M.; Du, L.; Liao, S. J. Recent advances in nanostructured transition metal nitrides for fuel cells. J. Mater. Chem. A 2020, 8, 20803-20818. doi: 10.1039/D0TA06995G

  24. [24]

      Theerthagiria, J.; Jun Lee, S.; Murthy, A. P.; Madhavan, J.; Choi, M. Y. Fundamental aspects and recent advances in transition metal nitrides as electrocatalysts for hydrogen evolution reaction: a review. Curr. Opin. Solid State Mater. Sci. 2020, 24, 100805. doi: 10.1016/j.cossms.2020.100805

  25. [25]

      Peng, X.; Pi, C.; Zhang, X. M.; Li, S.; Huo, K. F.; Chu, P. K. Recent progress of transition metal nitrides for efficient electrocatalytic water splitting. Sustain. Energy Fuels 2019, 3, 366-381. doi: 10.1039/C8SE00525G

  26. [26]

      Han, N.; Liu, P. Y.; Jiang, J.; Ai, L. H.; Shao, Z. P.; Liu, S. M. Recent advances in nanostructured metal nitrides for water splitting. J. Mater. Chem. A 2018, 6, 19912-19933. doi: 10.1039/C8TA06529B

  27. [27]

      Wang, H.; Li, J. M.; Li, K.; Lin, Y. P.; Chen, J. M.; Gao, L. J.; Nicolosi, V.; Xiao, X.; Lee, J. M. Transition metal nitrides for electrochemical energy applications. Chem. Soc. Rev. 2021, 50, 1354-1390. doi: 10.1039/D0CS00415D

  28. [28]

      Dong, S. M.; Chen, X.; Zhang, X. Y.; Cui, G. L. Nanostructured transition metal nitrides for energy storage and fuel cells. Coord. Chem. Rev. 2013, 257, 1946-1956. doi: 10.1016/j.ccr.2012.12.012

  29. [29]

      Dubal, D. P.; Chodankar, N. R.; Qiao, S. Z. Tungsten nitride nanodots embedded phosphorous modified carbon fabric as flexible and robust electrode for asymmetric pseudocapacitor. Small 2018, 15, 1804104.

  30. [30]

      Chen, Y. K.; Yu, J. Y.; Jia, J.; Liu, F.; Zhang, Y. W.; Xiong, G. W.; Zhang, R. T.; Yang, R. Q.; Sun, D. H.; Liu, H.; Zhou, W. J. Metallic Ni₃Mo₃N porous microrods with abundant catalytic sites as efficient electrocatalyst for large current density and superstability of hydrogen evolution reaction and water splitting. Appl. Catal., B 2020, 272, 118956. doi: 10.1016/j.apcatb.2020.118956

  31. [31]

      Yang, Z.; Hao, J. Progress in pulsed laser deposited two dimensional layered materials for device applications. J. Mater. Chem. C 2016, 4, 8859-8878. doi: 10.1039/C6TC01602B

  32. [32]

      Ramesh, R.; Nandi, D. K.; Kim, T. H.; Cheon, T.; Oh, J.; Kim, S. H.; Atomic-layer-deposited MoN_x thin films on three-dimensional Ni foam as efficient catalysts for the electrochemical hydrogen evolution reaction. ACS Appl. Mater. Interfaces 2019, 11, 17321-17332. doi: 10.1021/acsami.8b20437

  33. [33]

      Bereznai, M.; Tóth, Z.; Caricato, A. P.; Fernández, M.; Luches, A.; Majni, G.; Mengucci, P.; Nagy, P. M.; Juhász, A.; Nánai, L. Reactive pulsed laser deposition of thin molybdenum- and tungsten-nitride films. Thin Solid Films 2005, 473, 16-23. doi: 10.1016/j.tsf.2004.06.149

  34. [34]

      Shafiee, S. A.; Perry, S. C.; Hamzah, H. H.; Mahat, M. M.; Al-lolage, F. A.; Ramli, M. Z. Recent advances on metal nitride materials as emerging electrochemical sensors: a mini review. Electrochem. Commun. 2020, 120, 106828. doi: 10.1016/j.elecom.2020.106828

  35. [35]

      Qin, R.; Wang, P. Y.; Lin, C.; Cao, F.; Zhang, J. Y.; Chen, L.; Mu, S. C. Transition metal nitrides: activity origin, synthesis and electrocatalytic applications. Acta Phys. -Chim. Sin. 2021, 37, 2009099.

  36. [36]

      Zhong, Y.; Xia, X. H.; Shi, F.; Zhan, J. Y.; Tu, J. P.; Fan, H. J. Transition metal carbides and nitrides in energy storage and conversion. Adv. Sci. 2016, 3, 1500286. doi: 10.1002/advs.201500286

  37. [37]

      Han, L.; Feng, K.; Chen, Z. Self-supported cobalt nickel nitride nanowires electrode for overall electrochemical water splitting. Energy Technol. 2017, 5, 1908-1911. doi: 10.1002/ente.201700108

  38. [38]

      Strickland, K.; Miner, E.; Jia, Q. Y.; Tylus, U.; Ramaswamy, N.; Liang, W. T.; Sougrati, M. T.; Jaouen F.; Mukerjee, S. Highly active oxygen reduction non-platinum group metal electrocatalyst without direct metal-nitrogen coordination. Nat. Commun. 2015, 6, 7343. doi: 10.1038/ncomms8343

  39. [39]

      Tareen, A. K.; Priyanga, G. S.; Behara, S.; Thomas, T.; Yanga, M.; Mixed ternary transition metal nitrides: a comprehensive review of synthesis, electronic structure, and properties of engineering relevance. Progr. Solid State Chem. 2019, 53, 1-26. doi: 10.1016/j.progsolidstchem.2018.11.001

  40. [40]

      Chen, Q.; Wang, R.; Yu, M.; Zeng, Y.; Lu, F.; Kuang, X.; Lu, X.; Bifunctional iron-nickel nitride nanoparticles as flexible and robust electrode for overall water splitting. Electrochim. Acta 2017, 247, 666-673. doi: 10.1016/j.electacta.2017.07.025

  41. [41]

      Sun, W. H.; Bartel, C. J.; Arca, E.; Bauers, S. R.; Matthews, B.; Orvañanos, B.; Chen, B. R.; Toney, M. F.; Schelhas, L. T.; Tumas, W.; Tate, J.; Zakutayev, A.; Lany, S.; Holder, A. M.; Ceder, G. A map of the inorganic ternary metal nitrides. Nat. Mater. 2019, 18, 732-739. doi: 10.1038/s41563-019-0396-2

  42. [42]

      Hore, S.; Kaiser, G.; Hu, Y. S.; Schulz, A.; Konuma, M.; Gotz, G.; Sigle, W.; Verhoeven, A. Carbonization of polyethylene on gold oxide. J. Mater. Chem. 2008, 18, 5589. doi: 10.1039/b812430b

  43. [43]

      Zhu, Y. P.; Chen, G.; Zhong, Y. J.; Zhou, W.; Shao, Z. P. Rationally designed hierarchically structured tungsten nitride and nitrogen-rich graphene-like carbon nanocomposite as efficient hydrogen evolution electrocatalyst. Adv. Sci. 2017, 1700603.

  44. [44]

      Luo, J. M.; Tian, X. L.; Zeng, J. H.; Li, Y. W.; Song, H. Y.; Liao, S. J. Limitations and improvement strategies for early-transition-metal nitrides as competitive catalysts toward the oxygen reduction reaction. ACS Catal. 2016, 9, 6165-6174.

  45. [45]

      Tang, H. B.; Luo, J. M.; Tian, X. L.; Dong, Y. Y.; Li, J.; Liu, M. R.; Liu, L. N.; Song, H. Y.; Liao, S. J. Template-free preparation of 3D porous Co-doped VN nanosheet-assembled microflowers with enhanced oxygen reduction activity. ACS Appl. Mater. Interfaces 2018, 10, 11604-11612. doi: 10.1021/acsami.7b18504

  46. [46]

      Xu, K.; Chen, P. Z.; Li, X. L.; Tong, Y.; Ding, H.; Wu, X. J.; Chu, W. S.; Peng, Z. M.; Wu, C. Z.; Xie, Y. Metallic nickel nitride nanosheets realizing enhanced electrochemical. J. Am. Chem. Soc. 2015, 137, 4119-4125. doi: 10.1021/ja5119495

  47. [47]

      Zhao, D.; Cui, Z. T.; Wang, S. G.; Qin, J. W.; Cao, M. H. VN hollow spheres assembled from porous nanosheets for high-performance lithium storage and the oxygen reduction reaction. J. Mater. Chem. A 2016, 4, 7914-7923. doi: 10.1039/C6TA01707J

  48. [48]

      Zeng, R.; Yang, Y.; Feng, X. R.; Li, H. Q.; Gibbs, L. M.; DiSalvo, F. J.; Abruna, H. D. Nonprecious transition metal nitrides as efficient oxygen reduction electrocatalysts for alkaline fuel cells. Sci. Adv. 2022, 8, 1584. doi: 10.1126/sciadv.abj1584

  49. [49]

      Jin, H. Y.; Wang, X. S.; Tang, C.; Vasileff, A.; Li, L. Q.; Slattery, A.; Qiao, S. Z. Stable and highly efficient hydrogen evolution from seawater enabled by an unsaturated nickel surface nitride. Adv. Mater. 2021, 33, 2007508. doi: 10.1002/adma.202007508

  50. [50]

      Liu, B.; He, B.; Peng, H. Q.; Zhao, Y. F.; Cheng, J. Y.; Xia, J.; Shen, J. H.; Ng, T. W.; Meng, X. M.; Lee, C. S.; Zhang, W. J. Unconventional nickel nitride enriched with nitrogen vacancies as a high efficiency electrocatalyst for hydrogen evolution. Adv. Sci. 2018, 5, 1800406. doi: 10.1002/advs.201800406

  51. [51]

      Ma, T. Y.; Cao, J. L.; Jaroniec, M.; Qiao, S. Z. Interacting carbon nitride and titanium carbide nanosheets for high-performance oxygen evolution. Angew. Chem. Int. Ed. 2016, 55, 1138-1142. doi: 10.1002/anie.201509758

  52. [52]

      Luo, J. M.; Qiao, X. C.; Jin, J. T.; Tian, X. L.; Fana, H. B.; Yu, D. M.; Wang, W. L.; Liao, S. J.; Yu, N.; Deng, Y. J. A strategy to unlock the potential of CrN as highly active oxygen reduction reaction catalyst. J. Mater. Chem. A 2020, 8, 8575-8585. doi: 10.1039/C9TA14085A

  53. [53]

      Xu, L.; Deng, D. J.; Tian, Y. H.; Li, H. P.; Qian, J. C.; Wu, J. C.; Li, H. N. Dual-active-sites design of CoNx anchored on zinc-coordinated nitrogen-codoped porous carbon with efficient oxygen catalysis for high-stable rechargeable zinc-air batteries. Chem. Eng. J. 2020, 127321.

  54. [54]

      Zhang, N.; Cao, L. Y.; Feng, L. L.; Huang, J. F.; Kajiyoshi, K.; Li, C. Y.; Liu, Q. Q.; Yang, D.; He, J. J.; Co, N-Codoped porous vanadium nitride nanoplates as superior bifunctional electrocatalysts for hydrogen evolution and oxygen reduction reactions. Nanoscale 2019, 11, 11542-11549. doi: 10.1039/C9NR02637A

  55. [55]

      Tang, H. B.; Tian, X. L.; Luo, J. M.; Zeng, J. H.; Li, Y. W.; Song, H. Y.; Liao, S. J. Co-doped porous niobium nitride nanogrid as effective oxygen reduction catalyst. J. Mater. Chem. A 2017, 5, 14278-14285. doi: 10.1039/C7TA03677A

  56. [56]

      Yao, N.; Li, P.; Zhou, Z. R.; Zhao, Y. M.; Cheng, G. Z.; Chen, S. L.; Luo, W. Synergistically tuning water, and hydrogen binding abilities over Co₄N by Cr doping for exceptional alkaline hydrogen evolution electro-catalysis. Adv. Energy Mater. 2019, 9, 1902449. doi: 10.1002/aenm.201902449

  57. [57]

      Zhang, Y. Q.; Ouyang, B.; Xu, J.; Jia, G. C.; Chen, S.; Rawat, R. S.; Fan, H. J. Rapid synthesis of cobalt nitride nanowires: highly efficient and low-cost catalysts for oxygen evolution. Angew. Chem. Int. Ed. 2016, 128, 1-6. doi: 10.1002/ange.201510990

  58. [58]

      Li, F.; Tian, Y. H.; Su, S. B.; Wang, C. S.; Li, D. S.; Cai, D. D.; Zhang, S. Q. Theoretical and experimental exploration of tri-metallic organic frame-works (t-MOFs) for efficient electrocatalytic oxygen evolution reaction. Appl. Catal. B 2021, 299, 120665. doi: 10.1016/j.apcatb.2021.120665

  59. [59]

      Wang, C. S.; Chen, W. B.; Yuan, D.; Qian, S. S.; Cai, D. D.; Jiang, J. T.; Zhang, S. Q. Tailoring the nanostructure and electronic configuration of metal phosphides for efficient electrocatalytic oxygen evolution reactions. Nano Energy 2020, 69, 104453. doi: 10.1016/j.nanoen.2020.104453

  60. [60]

      Yang, Y.; Zeng, R.; Xiong, Y.; DiSalvo, F. J.; Abruña, H. D. Cobalt-based nitride-core oxide-shell oxygen reduction electrocatalysts. J. Am. Chem. Soc. 2019, 141, 19241-19245 doi: 10.1021/jacs.9b10809

  61. [61]

      Wu, A. Q.; Xie, Y.; Ma, H.; Tiana, C. G.; Yang, G. Y.; Fu, H. G. Integrating the active OER and HER components as the heterostructures for the efficient overall water splitting. Nano Energy 2018, 44, 353-363. doi: 10.1016/j.nanoen.2017.11.045

  62. [62]

      Yan, H. J.; Xie, Y.; Wu, A. P.; Cai, Z. C.; Wang, L.; Tian, C. G.; Zhang, X. M.; Fu, H. G. Anion-modulated HER and OER activities of 3D Ni-V-based interstitial compound heterojunctions for high-efficiency and stable overall water splitting. Adv. Mater. 2019, 31, 1901174. doi: 10.1002/adma.201901174

  63. [63]

      Sun, K. X.; Zhang, T.; Tan, L. M.; Zhou, D. X.; Qian, Y. Q.; Gao, X. X.; Song, F. H.; Bian, H. T.; Lu, Z.; Dang, J. S.; Gao, H.; Shaw, J.; Chen, S. T.; Ghen, G. G.; Rao, Y. Interface catalysts of Ni/Co₂N for hydrogen electrochemistry. ACS Appl. Mater. Interfaces 2020, 12, 26, 29357-29364.

  64. [64]

      Li, J. L.; Kong, X. G.; Jiang, M. H.; Lei, X. D. Hierarchically structured CoN/Cu₃N nanotube array supported on copper foam as efficient bifunctional electrocatalyst for overall water splitting. Inorg. Chem. Front. 2018, 5, 2906-2913. doi: 10.1039/C8QI00860D

  65. [65]

      Dong, X.; Yan, H. J.; Jiao, Y. Q.; Guo, D. Z.; Wu, A. P.; Yang, G. C.; Shi, X.; Tian, C. G.; Fu, H. G. 3D hierarchical V-Ni-based nitride heterostructure as a highly efficient pH-universal electrocatalyst for the hydrogen evolution reaction. J. Mater. Chem. A 2019, 7, 15823-15830. doi: 10.1039/C9TA04742E

  66. [66]

      Wang, C.; Lv, X. S.; Zhou, P.; Liang, X. Z.; Wang, Z. Y.; Liu, Y. Y.; Wang, P.; Zheng, Z. K.; Dai, Y.; Li, Y. J.; Whangbo, M. H.; Huang, B. B. Molybdenum nitride electrocatalysts for hydrogen evolution more efficient than platinum/carbon: Mo₂N/CeO₂@nickel foam. ACS Appl. Mater. Interfaces 2020, 12, 29153-29161.

  67. [67]

      Xu, L.; Sitinamaluwa, H.; Li, H. N.; Qiu, J. X.; Wang, Y. Z.; Yan, C.; Li, H. M.; Yuan, S. Q.; Zhang, S. Q. A low cost and green preparation process of α-Fe₂O₃ @gum arabic electrode for high performance sodium ion battery. J. Mater. Chem. A 2017, 5, 2102-2109. doi: 10.1039/C6TA08918F

  68. [68]

      Li, Z. L.; Zhuang, Z. C.; Lv, F.; Zhu, H.; Zhou, L.; Luo, M. C.; Zhu, J. X.; Lang, Z. Q.; Feng, S. H.; Chen, W.; Mai, L. Q.; Guo, S. J. The marriage of the FeN₄ moiety and MXene boosts oxygen reduction catalysis: Fe 3d electron delocalization matters. Adv. Mater. 2018, 30, 1803220. doi: 10.1002/adma.201803220

  69. [69]

      Cui, Z. M.; Fu, G. T.; Li, Y. T.; Goodenough, J. B. Ni₃FeN-supported Fe₃Pt intermetallic nanoalloy as a high-performance bifunctional catalyst for metal-air batteries. Angew. Chem. Int. Ed. 2017, 56, 9901-9905. doi: 10.1002/anie.201705778

  70. [70]

      Zhang, J.; Zhang, L.; Du, L.; Xin, H. L.; Goodenough, J. B.; Cui, Z. Composition-tunable antiperovskite Cu_xIn_1-xNNi₃ as superior electrocatalysts for the hydrogen evolution reaction. Angew. Chem. Int. Ed. 2020, 59, 17488-17493. doi: 10.1002/anie.202007883

  71. [71]

      Zhu, Y. P.; Chen, G.; Zhong, Y. J.; Chen, Y. B.; Ma, N. N.; Zhou, W.; Shao, Z. P. A surface-modified antiperovskite as an electrocatalyst for water oxidation. Nat. Commun. 2018, 9, 2326. doi: 10.1038/s41467-018-04682-y

  72. [72]

      Shein, I. R.; Ivanovskii, A. L. Electronic and elastic properties of non-oxide anti-perovskites from first principles: superconducting CdCNi₃In comparison with magneticInCNi₃. Phys. Rev. B 2008, 77, 104101. doi: 10.1103/PhysRevB.77.104101

  73. [73]

      Takenaka, K.; Takagi, H. Giant negative thermal expansion in Ge-doped anti-perovskite manganese nitrides. Appl. Phys. Lett. 2005, 87, 261902. doi: 10.1063/1.2147726

  74. [74]

      Guo, H. P.; Gao, X. W.; Yu, N. F.; Zheng, Z.; Luo, W. B.; Wu, C.; Liu, H. K.; Wang, J. Z. Metallic state two-dimensional holey-structured Co₃FeN nanosheets as stable and bifunctional electrocatalysts for zinc-air batteries. J. Mater. Chem. A 2019, 7, 26549-26556. doi: 10.1039/C9TA10079B

  75. [75]

      He, X. Y.; Tian, Y. H.; Huang, Z. L.; Xu, L.; Wu, J. C.; Qian, J. C.; Zhang, J. M.; Li, H. N. Engineering the electronic states of Ni₃FeN via zinc ion regulation for promoting oxygen electrocatalysis in rechargeable Zn-air batteries. J. Mater. Chem. A 2021, 9, 2301-2307. doi: 10.1039/D0TA10370E

  76. [76]

      Gu, Y.; Chen, S.; Ren, J.; Jia, Y. A.; Chen, C. M.; Komarneni, S.; Yang, D. J.; Yao, X. D. Electronic structure tuning in Ni₃FeN/r-GO aerogel toward bifunctional electrocatalyst for overall water splitting. ACS Nano 2018, 12, 245-253. doi: 10.1021/acsnano.7b05971

  77. [77]

      Jin, S. Are metal chalcogenides, nitrides, and phosphides oxygen evolution catalysts or bifunctional catalysts? ACS Energy Lett. 2017, 2, 1937-1938. doi: 10.1021/acsenergylett.7b00679

  78. [78]

      Ge, H. Y.; Li, G. D.; Shen, J. X.; Ma, W. Q.; Meng, X. G.; Xu, L. Q. Co₄N nanoparticles encapsulated in N-doped carbon box as tri-functional catalyst for Zn-air battery and overall water splitting. Appl. Catal. B 2020, 275, 119104. doi: 10.1016/j.apcatb.2020.119104

  79. [79]

      Liu, L. N.; Yan, F.; Li, K. Y.; Zhu, C. L.; Xie, Y.; Zhang, X. T.; Chen, Y. J. Ultrasmall FeNi₃N particles with an exposed active (110) surface anchored on nitrogen-doped graphene for multifunctional electrocatalysts. J. Mater. Chem. A 2019, 7, 1083-1091. doi: 10.1039/C8TA10083G

  80. [80]

      Dong, Y. Y.; Deng, Y. J.; Zeng, J. H.; Song, H. Y.; Liao, S. J. A high-performance composite ORR catalyst based on the synergy between binary transition metal nitride and nitrogen-doped reduced graphene oxide. J. Mater. Chem. A 2017, 5, 5829-5837. doi: 10.1039/C6TA10496G

  81. [81]

      Yuan, W. Y.; Wang, S. Y.; Ma, Y. Y.; Qiu, Y.; An, Y. R.; Cheng, L. F. Interfacial engineering of cobalt nitrides and mesoporous nitrogen-doped carbon: toward efficient overall water-splitting activity with enhanced charge-transfer efficiency. ACS Energy Lett. 2020, 5, 692-700. doi: 10.1021/acsenergylett.0c00116

  82. [82]

      Chen, L. L.; Zhang, Y. L.; Liu, X. J.; Long, L.; Wang, S. Y.; Xu, X. L.; Liu, M. C.; Yang, W. X.; Jia, J. B. Bifunctional oxygen electrodes of homogeneous Co₄N nanocrystals@N-doped carbon hybrids for rechargeable Zn-air batteries. Carbon 2019, 15, 10-17.

  83. [83]

      He, X. Y.; Tian, Y. H.; Deng, D. J.; Chen, F.; Wu, J. C.; Qian, J. C; Li, H. N.; Xu, L. Engineering anti-perovskite Ni₄N/VN heterostructure with improved intrinsic interfacial charge transfer as a bifunctional catalyst for rechargeable zinc-air batteries. ACS Sustain. Chem. Eng. 2021, 9, 17007-17015. doi: 10.1021/acssuschemeng.1c05907

  84. [84]

      Xu, L.; Wu, S. Q.; He, X. Y.; Wang, H.; Deng, D. J.; Wu, J. C.; Li, H. N. Interface engineering of anti-perovskite Ni₃FeN/VN heterostructure for high-performance rechargeable Zn-air batteries. Chem. Eng. J. 2022, 437, 135291. doi: 10.1016/j.cej.2022.135291

  85. [85]

      Zhang, J. X.; Zhao, X.; Du, L.; Li, Y. T.; Zhang, L. H.; Liao, S. J.; Goodenough, J. B.; Cui, Z. M. Antiperovskite nitrides CuNCo_3-xV_x: highly efficient and durable electrocatalysts for the oxygen-evolution reaction. Nano Lett. 2019, 19, 7457-7463. doi: 10.1021/acs.nanolett.9b03168

  86. [86]

      Jin, T.; Sang, X. H.; Unocic, R. R.; Kinch, R. T.; Liu, X. F.; Hu, J.; Liu, H. L.; Dai, S. Mechanochemical-assisted synthesis of high-entropy metal nitride via a soft urea strategy. Adv. Mater. 2018, 30, 1707512. doi: 10.1002/adma.201707512

  87. [87]

      Li, S. Q.; Sun, X.; Yao, Z. H.; Zhong, X.; Cao, Y. Y.; Liang, Y. L.; Wei, Z. Z.; Deng, S. W.; Zhuang, G. L.; Li, X. N.; Wang, J. G. Biomass valorization via paired electrosynthesis over vanadium nitride-based electrocatalysts. Adv. Funct. Mater. 2019, 29, 1904780. doi: 10.1002/adfm.201904780

  88. [88]

      Kuttiyiel, K. A.; Sasaki, K.; Choi, Y. M.; Su, D.; Liu, P.; Adzic, R. R. Nitride stabilized PtNi core-shell nanocatalyst for high oxygen reduction activity. Nano Lett. 2012, 12, 6266-6271. doi: 10.1021/nl303362s

  89. [89]

      Liu, F. F.; Yang, X.; Dang, D.; Tian, X. L. Engineering of hierarchical and three-dimensional architectures constructed by titanium nitride nanowire assemblies for efficient electrocatalysis. ChemElectroChem 2019, 6, 2208-2214. doi: 10.1002/celc.201900252

  90. [90]

      Lai, S. J.; Xu, L.; Liu, H. L.; Chen, S.; Cai, R. S.; Zhang, L. J.; Theis, W.; Sun, J.; Yang, D. J.; Zhao, X. L. Controllable synthesis of CoN₃ catalysts derived from Co/Zn-ZIF-67 for electrocatalytic oxygen reduction in acidic electrolytes. J. Mater. Chem. A 2019, 7, 21884-21891. doi: 10.1039/C9TA08134H

  91. [91]

      Kim, B. G.; Jo, C. S. Shin, J.; Mun, Y. D.; Lee, J.; Choi, J. W. Ordered mesoporous titanium nitride as a promising carbon-free cathode for aprotic lithium-oxygen batteries. ACS Nano 2017, 11, 2, 1736-1746.

  92. [92]

      Zou, H. Y.; Li, G.; Duan, L. L.; Kou, Z. K.; Wang, J. In situ coupled amorphous cobalt nitride with nitrogen-doped graphene aerogel as a trifunctional electrocatalyst towards Zn-air battery deriven full water splitting. Appl. Catal. B 2019, 259, 118100. doi: 10.1016/j.apcatb.2019.118100

  93. [93]

      Song, J. N.; Yu, D. H.; Wu, X. L.; Xie, D. Y.; Sun, Y.; Vishniakov, P.; Hu, F.; Li, L. L.; Li, C. S.; Maximov, M. Y.; Maximov, K. M.; Peng, S. J. Interfacial coupling porous cobalt nitride nanosheets array with N-doped carbon as robust trifunctional electrocatalysts for water splitting and Zn-air battery. Chem. Eng. J. 2022, 437, 1, 135281.

• 

  Figure 1  (a) Schematic illustration, (b-d) XRD patterns and (e) ORR LSV tests in O₂-saturated 1 mol·L^-1 KOH for carbon-supported TMNs (M_xN/C); Copyright 2022, Science. (f) Ni 2p and (g) N 1s XPS spectra for Ni-SN@C; (h) Synchrotron based N K edge and (i) HER LSV tests in 1 mol·L^-1 KOH for Ni-SN@C; Copyright 2021, WILEY-VCH.

  下载: 全尺寸图片 幻灯片
  

  Figure 2  (a) N-determined competitive mechanism; (b) Electron-transfer model of V_0.95Co_0.05Ns for ORR activity; ORR LSV tests in 0.1 mol·L^-1 (c) HClO₄ and (d) KOH for VN and V_0.95M_0.05Ns catalysts; Copyright 2016, American Chemical Society. (e) Schematic illustration, (f) electron-transfer model for ORR activity and (g) ORR LSV tests in 0.1 mol·L^-1 KOH of V_0.95Co_0.05N MFs; Copyright 2018, American Chemical Society. (h) HR-TEM image, (i) XRD pattern, (j) electrocatalytic HER performance and (k) calculated adsorption energy for H₂O of Ni₃N-VN/NF; Copyright 2019, WILEY-VCH.

  下载: 全尺寸图片 幻灯片
  

  Figure 3  (a) HR-TEM image, (b) XRD pattern and (c) ORR LSV tests in 0.1 mol·L^-1 KOH solution of CoN_x/Zn-NC; Copyright 2019, Elsevier. (d) XRD pattern, (e) ORR LSV curves and (f) OER LSV curves in 0.1 mol·L^-1 KOH for Zn-Ni₃FeN/NG; Copyright 2021, Royal Society of Chemistry. (g) HR-TEM image, (h) OER and (i) HER LSV curves in 1.0 mol·L^-1 KOH for Ni₃FeN/r-GO-20; Copyright 2018, American Chemical Society.

  下载: 全尺寸图片 幻灯片
  

  Figure 4  (a) XRD patterns and (b) side view of Co₄N@NC model system (The yellow, gray, and green balls are presented in Co, C and N atoms, respectively.), (c) DOS of Co₄N@NC Co₄N and NC; Copyright 2020, American Chemical Society. (d) XRD pattern, (e) ORR LSV test and (f) OER LSV test 0.1 mol·L^-1 KOH for Co₄N@NC-m; Copyright 2019, Elsevier.

  下载: 全尺寸图片 幻灯片
  

  Figure 5  (a) Unit cell models and (b) OER LSV tests in 1.0 mol·L^-1 KOH of CuNCo₃ and CuNCo_3-xV_x; Copyright 2019, American Chemical Society. (c) 2×2 unit cell models and (d) HER LSV tests in 1.0 mol·L^-1 KOH of InNNi₃ and Cu_0.5In_0.5NNi; Copyright 2019, American Chemical Society. (e) Schematic illustration and (f) EDS elemental maps of HEMN-1; Copyright 2018, WILEY-VCH.

  下载: 全尺寸图片 幻灯片
  

  Figure 6  (a) XRD patterns, (b) ORR and (c) OER LSV test in 0.1 mol·L^-1 KOH of Fe₃Pt/Ni₃FeN and Ni₃FeN; Copyright 2017, Wiley-VCH. (d) XRD pattern, (e) HAADF image and (f) ORR LSV test in 0.1 mol·L^-1 HClO₄ of PtNiN/C; Copyright 2012, American Chemical Society. (g-h) TEM images and (i) ORR LSV test in 0.1 mol·L^-1 HClO₄ of Pt/3D TiN; Copyright 2019, Wiley-VCH.

  下载: 全尺寸图片 幻灯片
  

  Figure 7  (a) XRD pattern of CoN₃@NC-7-1000, (b) H₂/O₂ and H₂/air fuel cell performances for CoN₃@NC-7-1000, (c) the durability tests of H₂/air fuel cells based on CoN₃@NC-7-1000 catalyst; Copyright 2019, Royal Society of Chemistry. (d) HR-TEM image and (e) HER/OER curves of Ni₃FeN/r-GO-20, (f) the stability test of time-current density for Ni₃FeN/r-GO-20 in a two-electrode configuration at 1.60 V; Copyright 2017, American Chemical Society.

  下载: 全尺寸图片 幻灯片
•