Rational design of nanocatalysts for ambient ammonia electrosynthesis

Nano-structure construction and nanoconfinement

Recently, CoMoC nanoporous catalysts [26], FeMo₃S₄ nanorods [27], FeMoO4 nanorods [28], CrN nanocube [29], Fe₂(MoO₄)₃ nanoparticles [30], molybdenum nitride (MoN₂) nanosheet [31], three-dimensional Pd-Ag-S porous nanosponges [32], two-dimensional MXenes [33], MoO2 nanoparticles supported by carbon nanowires [34], Au nanocrystals [35], bimetallic Au-Ag nanocages [36], NiCoS/C nanocages [37], AuPdP Nanowires [38], amorphous CoMoO₄ catalysts with nanoporous structures [39], palladium nanothorn assembly array [40], VN nanowire array on carbon cloth [41] and nanorod-structured MoN [42] have been used as efficient for NRR under ambient conditions. It indicated that nano-structure construction and nanoconfinement are efficient method for the design of electrocatalysts for NRR.

Nazemi et al. [43] enhanced the rate of NRR by the design of hollow Au nanocages (AuNCs). It achieved the highest FE of 30.2 % and the highest yield rate of 3.9 μg cm⁻² h⁻¹ in 0.5 M LiClO₄ aqueous solution. Compared with Au nanocubes, nanospheres, and nanorods, the AuNCs had the highest catalytic efficiency. The increased amount of valency-unsatisfied surface atoms with sharper edges and corners of AuNCs provided much more active sites for NRR. On the other hand, the increasing surface area and confinement of reactants in the cavity extended the residence time of N₂ molecules on the nanoparticle inner surface.

Li et al. [44]. reported that the dendritic Cu was a high-efficiency electrocatalyst for NRR with a high NH₃ yield rate of 25.63 μg mg⁻¹ h⁻¹ and a FE of 15.12 % at −0.4 V vs. RHE in 1 M HCl electrolyte. The dendritic Cu nanostructures with rich orientation tips and high surface area can serve as an efficient electrocatalyst. The spikes on the material surface significantly amplified the local electric field, leading to improvement of reagent concentration near electrode tips [45, 46]. This special structure greatly facilitated the interaction between electrocatalysts and reactants by providing a great number of active sites.

Xue et al. [47] reported an efficient NRR catalyst that was composed of the donor-acceptor couples of Ni and Au nanoparticles supported on nitrogen-doped carbon. It can achieve a maximum NH₃ production rate of 7.4 μg h⁻¹ mg⁻¹ with a high Faradaic efficiency of 67.8 % at −0.14 V vs. RHE. It is worth noting that Au₆/Ni is superior to the other electrocatalysts with various atomic ratios of the Au-Ni couples and Au- [48], Ru- [49], or Pd-based [50] electrocatalysts. The highly coupled Au and Ni nanoparticles loaded on carbon make the catalyst have long-term and reusable NRR stability, leading to the electrochemical processes more sustainable in practical applications. From the experimental and theoretical results, it can be known that the as-formed electron-rich Au species can accept electrons from Ni species, and thus facilitating the adsorption, activation and dissociation of N₂ molecule. The work gave a guideline for the fabrication of electrocatalysts for NRR via the construction of metal-metal donor-acceptor couples.

Pd-Ru bimetallic porous nanostructures (Pd-Ru BPNs) were used as electrocatalysts for NRR with a FE of 1.53 % at −0.1 V in 0.1 M HCl and prominent stability. A high NH₃ yield rate of 25.92 μg mg⁻¹ h⁻¹ was obtained, which was 4.2 times higher than that of monometallic Pd and 2.5 times than that of monometallic Ru (Fig. 4) [51]. The scanning electron microscopy (SEM) image of Pd-Ru BPNs revealed that it consisted of porous structures with interconnected networks (Fig. 4(a)). The transmission electron microscope (TEM) further supported that the morphology of the Pd-Ru BPNs possessed fused architectures (Fig. 4(b)). As shown in Fig. 4(c), the average size of Pd-Ru BPNs was approximately 4–6 nm with well-defined crystal lattices which were detected by the high-resolution transmission electron microscopy (HRTEM). As shown in Fig. 4(d), the fast Fourier transform (FFT) patterns observed an interplanar spacing of 0.223 nm indexed to the (111) crystal plane of the PdRu BPNs. All above results indicated that Pd-Ru BPNs had been synthesized. Pd-Ru BPNs were prepared by the co-reduction of Pd and Ru precursors, and the coordination environments and electronic states of Pd and Ru can be also tailored by bimetallic nanostructures. The three-dimensional interconnected porous nanostructures did not only increase the number of active sites and enhanced the interaction of the adsorbed N species to facilitate NRR, but also effectively prevented the agglomeration of Pd-Ru to improve the long-term durability.

Fig. 4:

(a–c). SEM, TEM, and HRTEM images of the PdRu BPNs. (d). The lattice fringes and corresponding FFT pattern of the square area in (c).

Reprinted with permission from Ref. [51]. Copyright 2019 American Chemical Society.

Shi et al. [52] anchored Pd–Cu amorphous nanoclusters on reduced graphene oxide (rGO), and the synergistic effects of the components in Pd_0.2Cu_0.8/rGO composites played a significant role in facilitating the electrocatalytic NRR performance. The NH₃ yield rate was 2.80 μg h⁻¹ mg_cat⁻¹ at a low overpotential of −0.2 V vs. RHE. It was 2.1 times higher than Pd/rGO, 2.4 times higher than Cu/rGO and 3.2 times higher than Pd_0.2Cu_0.8/NPs. Pd can be used as a nitrogen-fixing catalyst, but Pd inclined to bind H adatoms compared with N ones. The introduction of Cu accelerated H desorption to prevent Pd from being covered by H. Compared with pure metal Pd or Cu, the bimetallic Pd–Cu increased the possibility of NRR. The electronic interaction between Pd and Cu also changed the electronic states of metal atoms and produced new catalytic centers obviously, and thus improving the catalytic activity. On the other hand, the dangling bonds on amorphous materials provided more active sites, which further increased the possibility of N₂ molecular activation. Furthermore, the addition of rGO support enhanced the dispersion of the catalytic sites, and improved N₂ molecules adsorption capacity.

The nanoporous palladium hydride (Pd–H) was also designed as electrocatalyst for NRR [53]. A high yield rate of 20.4 μg mg⁻¹ h⁻¹ and a high FE of 43.6 % for NH₃ production was achieved at −0.2 V vs. RHE in 0.1 M HCl. Compared with the pristine Pd, the NRR activity and selectivity of nanoporous Pd-H hydrides were significantly improved. The hydrogenation of Pd effectively altered the d-electron center and enhanced the catalytic activity. The study revealed that NH₃ was formed through the reaction of N adsorbed and H extracted from the outermost Pd–H lattice, and then H vacancies can be repaired by activating H₂O.

Cr₂O₃ was viewed as an excellent non-noble-metal catalyst for NRR. Cr₂O₃ nanofiber affords a high FE of 8.56 % and a high NH₃ formation rate of 28.13 μg h⁻¹ mg_cat⁻¹ in 0.1 M HCl. Cr₂O₃ nanoparticle-reduced graphene oxide hybrid (Cr₂O₃-rGO) also showed excellent selectivity and stability for NH₃ synthesis with a high NH₃ yield (33.3 μg h⁻¹ mg_cat⁻¹, −0.7 V (RHE)) and a high FE (7.33 %, −0.6 V (RHE)). Zhang et al. [54] reported that multi-shelled hollow Cr₂O₃ microspheres (MHCMs) had a high yield rate of 25.3 μg h⁻¹ mg_cat⁻¹ and a high FE of 6.78 % for NH₃ electrosynthesis. It was higher than the corresponding Cr₂O₃ nanoparticles (13.8 μg h⁻¹ mg_cat⁻¹, 4.73 %) and Cr₂O₃ microspheres (11.4 μg h⁻¹ mg_cat⁻¹, 2.94 %), respectively. MHCMs showed good electrochemical and structural stability during NRR (Fig. 5). The X-ray diffraction (XRD) pattern of MHCMs (Fig. 5(a)) described the characteristic peaks of the Cr₂O₃ phase. Figure 5(b) and (c) showed the SEM images of precursor consists of microspheres with smooth surface and broken spheres with smaller size after the precursor was calcinated in air. Figure 5(d) and (e) showed the TEM images of darker periphery and lighter regions of MHCM indicating the structure of Cr₂O₃ was multishelled hollow microsphere. HRTEM image (Fig. 5(f)) revealed the lattice fringe and the interval was determined as 0.248 nm indexed to the (110) plane of Cr₂O₃ phase. Figure 5(g) described the scanning TEM (STEM) image of MHCM. As shown in Fig. 5(h) and (i), the images of Energy-dispersive X-ray (EDX) revealed that Cr and O elements were uniformly distributed on the MHCM. On the one hand, the hollow structure of the MHCMs exposed a large number of active sites and enhanced the diffusion of N₂, the intermediates and products [55]. On the other hand, the hollow structure also facilitated the frequency collisions and residence time in the inner surface. As a result, MHCMs showed preferable electrocatalytic activity for NRR.

Fig. 5:

(a) XRD pattern of MHCMs. SEM images of (b) the precursor of MHCMs and (c) MHCMs. (d, e) TEM images indifferent magnifications of a single MHCM. (f) HRTEM image of MHCM. (g) STEM image of MHCM and EDX elemental mapping of (h) Cr and (i) O.

Reprinted with permission from Ref. [54]. Copyright 2018 American Chemical Society.

Han et al. [56]. designed Nb₂O₅ nanofiber for N₂ fixation to NH₃ at ambient conditions. At −0.55 V vs. RHE, Nb₂O₅ nanofiber showed a high average yield rate of 43.6 μg h⁻¹ mg_cat⁻¹ compared with the NH₃ yield of commercial Nb₂O₅ (8.9 μg h⁻¹ mg_cat⁻¹), a superior FE of 9.26 %, and outstanding electrochemical stability in 0.1 M HCl. It can be attributed to its porous surface, which exposed more active sites and enhanced the diffusion of N₂ and product.

Wu et al. [57]. synthesized Mn₃O₄ nanocube as electrocatalyst for NRR. It had a FE of 3.0 % and a NH₃ yield of 11.6 μg h⁻¹ mg_cat⁻¹ at −0.80 V vs. RHE in 0.1 M Na₂SO₄. Furthermore, this catalyst also possessed satisfactory electrochemical and structural durability. Li et al. [58] reported spinel LiMn₂O₄ nanofiber as electrocatalyst for NRR under ambient conditions, achieving a high NH₃ yield rate of 15.83 μg h⁻¹ mg_cat⁻¹ at −0.5 V vs. RHE in 0.1 M HCl. Meanwhile, it also showed excellent electrochemical and structure stability.

Zhao et al. [59] designed Fe nanodot-decorated MoS₂ nanosheets as an efficient electrocatalyst for N₂ fixation to NH₃ at ambient conditions. It achieved a high yield rate of 12.5 mg h⁻¹ cm⁻² and a FE of 10.8 % at −0.1 V vs. RHE. Furthermore, it showed an excellent long-term stability.

Doping and defects engineering

Doping and defects construction are common method in the design of catalysts for NRR. A large amount of efficient electrocatalysts have been designed and prepared, such as O-doped graphdiyne [60], metal-organic-framework-derived Co-doped carbon [61], Fe-doped phosphorene [62], nitrogen vacancies on 2D layered W2N3 [63], Mo-doped g-GaN monolayer [64], O-doped molybdenum carbide nanoparticles [65], nitrogen-doped NiO nanosheet [66], P-Doped graphene [67] and P-doped WO3 flowers [68].

Boron (B) is an important doping element. The B-doped graphene catalysts [69] can attain a yield rate of NH₃ formation of 9.8 μg h⁻¹ cm⁻² and a FE of 10.8 % in aqueous solutions at −0.5 V vs. RHE. The NH₃ yield and FE of B-doped was 5-fold and 10-fold higher than that of undoped graphene, respectively. The original sp2 hybridization and conjugated planar structure graphene framework doped with B atoms were retained. B doping led to electron redistribution and induced electron deficiency, resulting in a great enhancement in electrocatalytic activity. The positively charged B atom provided ideal catalytic centers for the formation of B-N bonds and subsequent production of NH₃ by facilitating the adsorption of N₂.

Qiu et al. [70] synthesized B₄C nanosheets decorated with in situ-derived B-doped graphene quantum dots for NRR. It showed a NH₃ yield rate of 28.6 μg h⁻¹ mg⁻¹ and a FE of 16.7 % in 0.1 M HCl under ambient conditions. Quantum dots are important components of electrocatalysts due to their large number of exposed edge positions and unique electronic properties [71]. The B-doped graphene quantum dots exhibited large N₂ adsorption capacity and enhanced charge transfer processes, which can enhance the electrocatalytic activity for N₂-to-NH₃ conversion.

Wang et al. [72] found that B-doped TiO₂ had a highly efficient NRR performance (3.4 % at −0.8 V vs. RHE) and outstanding electrochemical durability (Fig. 6). The XRD images of pristine TiO₂ and B-TiO₂ indicated the increase of TiO₂ crystallinity as shown in Fig. 6(a). Figure 6(b) revealed the morphology of B-TiO₂ was sphere with strong agglomeration by SEM. As shown in Fig. 6(c), the EDX images revealed the uniformed distribution of Ti and O elements and low content of B was detected in the surface of particles. The TEM image revealed the sphere nature of B-TiO₂ (Fig. 6(d)). As shown in Fig. 6(e), the lattice fringe was determined as 0.35 nm indexed to the (101) plane of TiO₂ by HRTEM. And four diffraction rings indexed to the (101), (103), (200) and (211) planes of the TiO₂ phase were observed by the selected area electron diffraction (SAED). The activity was higher than pristine TiO₂ and TiO₂ nanosheets. B-TiO₂ presented higher specific surface area and exposed active sites. It can promote the electrochemical performance via the formation of oxygen vacancies. A suitable amount of B doped in TiO₂ may change the semiconductor properties of intrinsic TiO₂, which improved the conductivity of TiO₂ and contributed to electron transfer from catalyst to N₂.

Fig. 6:

(a) XRD patterns for B-TiO₂ and TiO₂. (b) SEM images of B-TiO₂. (c) SEM and EDX elemental mapping images of Ti, O and B for BTiO₂. (d) TEM image for one single B-TiO₂ particle. (e) HRTEM image and (f) SAED pattern taken from B-TiO₂.

Reprinted with permission from Ref. [72]. Copyright 2019 American Chemical Society.

Wang et al. [73] biomimetically designed a Mo(IV)-doped FeS₂ nanosheet for NRR. It showed a high NH₃ FE of 14.41 % and a yield rate of 25.15 μg h⁻¹ mg⁻¹ at −0.2 V vs. RHE (Fig. 7). SEM images (Fig. 7(a)) showed that the catalyst was composed of thin nanosheets. Energy dispersive spectrometer (EDS) mapping revealed that the distribution of Fe, Mo, and S are homogenous (Fig. 7(b)). High-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) image indicated separated bright spots assigned as Mo sites as shown in Fig. 7(c). XRD (Fig. 6(d)) images of FeS₂-Mo_x is consistent with that of pyrite FeS₂. Raman spectrum (Fig. 7(e)) of FeS₂-Mo_17.3 was almost consistent with that of FeS₂. A red shift of 10 cm⁻¹ generated for the depression of Fe-S vibration by Mo doping. The valence state (+4) of Mo cations in FeS₂-Mo_17.3 was the same as those in MoS₂ according to the X-ray photoelectron spectroscopy (XPS) images (Fig. 7(f)). The adsorption and activation of N₂ was promoted by the Mo(IV) ions, and the competitive HER was depressed by the FeS₂ substrate. It has been demonstrated that Mo(IV) could be used as the active site for N₂ fixation due to its unoccupied d orbitals.

Fig. 7:

Characterizations of FeS₂-Mo_17.3 nanosheets.

(a) SEM image, (b) EDS mapping, (c) HAADF-STEM image, the inset is the intensity profile of the atoms along the dot line, and the red circles indicate the Mo cations, (d) XRD patterns of FeS₂-Mo_17.3 and FeS₂ nanosheets, (e) Raman spectra of FeS₂-Mo_17.3 and FeS₂ nanosheets, and (f) Mo 3d core-level XPS spectra of FeS₂-Mo_17.3 and MoS₂. Reprinted with permission from Ref. [73]. Copyright 2020 American Chemical Society.

Li et al. [74] designed a defect-rich MoS₂ nanoflower with the high catalytic performance and strong electrochemical stability for NRR (Fig. 7). In 0.1 M Na₂SO₄, it achieved a high NH₃ yield rate of 29.28 μg h⁻¹ mg_cat⁻¹ and a FE of 8.34 % at −0.40 V vs. RHE, superior to defect-free counterpart (13.41 μg h⁻¹ mg_cat⁻¹ and 2.18 %). It has been found that the potential determination step of the defect-rich catalyst had a lower energy barrier (0.60 eV) compared to the defect-free catalyst (0.68 eV) according to density functional theory calculations. The defects evolved the boundaries of the crystal to eliminate strain, leading to the lattice expansion. They offered more active unsaturated atoms and powerfully affected the electronic structure. For example, the defects caused the center of the d band shift to the Fermi level (−0.26 eV → −0.14 eV), resulting in boosting the interaction between the catalyst surface and N₂ molecules.

Single-atom engineering

To solve the significant challenge of N₂ fixation under ambient conditions, Tao et al. [75] studied single-atom Ru as an electrocatalyst for NRR. When ZrO₂ was used as support, a remarkably large NH₃ FE of up to 21 % can be obtained. It has been found that the addition of ZrO₂ significantly suppressed the competitive HER. The Ru sites with oxygen vacancies were the main active sites, and their high catalytic performance can be attributed to the stabilization of *NNH (low overpotential), the violent instability of *H (high NRR/HER selectivity) and N₂ adsorption enhancement (initiation of the NRR process).

Qin et al. [76] synthesized single-site Au catalysts on hierarchical N-doped porous carbon (NDPCs) for NRR. It showed a NH₃ yield rate of 2.32 μg h⁻¹cm⁻² and a FE of 12.3 % (Fig. 8).Compared with heteroatom-free porous carbon, NDPCs can stabilize the single metal sites at high loadings. This highly polarized porous carrier can be used to boost N₂ adsorption and mass transfer [77]. It has been reported that the dissociation of N₂ can be enhanced by N species in the NDPCs.

Fig. 8:

Materials characterization of copper-nickel alloy catalysts.

(a, b) Representative SEM and HRTEM images of the Cu₅₀Ni₅₀ catalyst. (c, d) Representative SEM and HRTEM images of the pure Cu catalyst. The scale bars are 200 nm in (a) and (c), and 10 nm in (b) and (d). (e–h) STEM image and EELS mapping analysis of the Cu₅₀Ni₅₀ catalyst. The scale bars are 100 nm. (i, j) XRD patterns and XPS Cu 2p spectra of catalysts with different Cu:Ni ratios. Reprinted with permission from Ref. [88]. Copyright 2020 American Chemical Society.

Using first-principles calculations, Tang et al. [78] reported that single transition metals (TM) atom sandwiched between hexagonal boron nitride (h-BN) and graphene sheets (BN/TM/G) acted as catalysts for NRR. TM atoms can provide electrons to adjacent B atoms as active sites. N≡N strong bond was weakened through B-to-N π-back bonding between the partially occupied pz orbital of a B atom and the antibonding state of N₂. The not-strong-not-weak electric field on the h-BN surface greatly enhanced the adsorption and activation of N₂. All above results provided an attractive way for triggering and modulating the activity of an inert BN sheet and created a new possibility of enhancing NH₃ production.

Fe-(O-C2)4 single-atom [79], single Mo atom supported on defective BC2N monolayers [80], single Mo atom supported on graphene [81], single-Mo-atom-embedded-graphdiyne monolayer with ultra-low onset potential [82],single Mo atom anchored on N-doped carbon [83], single-atom Pd sites with Cu [84], graphene-boron nitride hybrid-supported single Mo atom [85], single atoms of iron on MoS2 nanosheets [7], single Au/Fe atoms supported on nitrogen-doped porous carbon [86] and copper single atoms anchored in porous nitrogen-doped carbon [87] are also used as efficient for NRR under ambient conditions.

Nano-structure construction and nanoconfinement

Wang et al. [88] enhanced nitrate-to-NH₃ activity of Cu-Ni alloys through the tuning of intermediate adsorption. The electrocatalyst achieved a high FE of 99 ± 1 % in the mixture of 100 mM KNO₃ and 1 M KOH electrolyte at −0.15 V vs. RHE (Fig. 8). The Cu₅₀Ni₅₀ catalyst exhibited dendritic morphologies according to SEM images (Fig. 8(a)). HRTEM images of the Cu₅₀Ni₅₀ catalyst (Fig. 8(b)) showed that lattice spacings of 0.208 and 0.179 nm for the Cu(111) and Cu(200) facets. Fig. 8(d) described the HRTEM image of the pure Cu catalyst which exhibited the lattice spacings of 0.210 and 0.181 nm for Cu(111) and Cu(200) facets that agree with cubic Cu. As shown in Fig. 8(e)–(h), the Cu-to-Ni ratio in the Cu₅₀Ni₅₀ catalyst was 52:48. A decrease of Cu lattice spacings was shown when Ni was incorporated (Fig. 8(i)). XPS (Fig. 8(j)) presented a remarkable decrease of Cu 2p binding energy and an important increase of Ni 2p binding energy for the alloyed catalysts. The activity of Cu₅₀Ni₅₀ alloy catalysts corresponded to 6-fold increase in activity of pure Cu. The introduction of Ni atoms shifts the potential-dependent step (PDS) from NO₃ adsorption to NH₂ hydrogenation, reducing the overpotential.

Rai et al. [89] adopted Ni nanoparticles immobilized on Fe₃O₄@n-SiO₂@h-SiO₂-NH₂ (a magnetic hierarchical mesoporous amine-functionalized (M-HMAF) silica) support to realize efficient and selective catalytic nitrate to NH₃ at room-temperature. Notably, the Ni/M-HMAF silica possessed the capacity of superb dispersion of Ni nanoparticles over the support. The electrocatalysts exhibited a noteworthy catalytic turnover frequency of 275 mmol g⁻¹ h⁻¹.

Doping and defects engineering

Jia et al. [90] reported that TiO₂ nanotubes with rich oxygen vacancies (TiO_2−x) can be regarded as an efficient electrocatalyst for boosting nitrate electroreduction to NH₃. It achieved a high FE of 85.0 %, a good selectivity of 87.1 % and an excellent conversion of 95.2 % at −1.6 V vs. saturated calomel electrode (SCE) (Fig. 9). The ammonium selectivity and yield of TiO_2−x were stable according to Fig. 9(a) and (b). Furthermore, Fig. 9(c) and (d) showed that the post-test TiO_2−x possessed the tubular morphology and anatase structure with abundant oxygen vacancies. TiO_2−x had tubular morphology and anatase structure with abundant oxygen vacancies (OVs). OVs weakened the N–O bond and inhibited the formation of by-products, which resulted in excellent selectivity.

Fig. 9:

(a) Selectivity and (b) yield rate of ammonium after consecutive recycling test. (c) XRD pattern of post-test TiO_2−x. (d) UV–vis absorption spectra of TiO_2−x and post-test TiO_2−x. Reprinted with permission from Ref. [90]. Copyright 2020 American Chemical Society.

Li et al. [91] designed Ru/O-doped-Ru core/shell nanoclusters as efficient NH₃ electrosynthesis catalysts from nitrate. The electrocatalyst showed a high NH₃ yield rate of 5.56 mol g_cat⁻¹ h⁻¹, which was obviously higher than that of Haber-Bosch process. The strained Ru nanoclusters were equipped with the characteristic of building a firm bonding between the Ru and subsurface O dopants. The O dopants can trigger tensile strains by expanding Ru unit cell. The strain unit cells inhibited HER. However, the strains facilitated the barrier of H–H coupling to promote the formation of •H. Hydrogen radicals are major contributors to this high catalytic performance, enhancing the hydrogenation of reaction intermediates to NH₃ at lower kinetic barriers. As a result of stable subsurface Ru-O coordination, it was possible for the strained nanostructures to maintain nearly 100 % ammonia-evolving selectivity at >120 mA cm⁻² current densities for 100 h.

Single-atom engineering

Feng et al. [92] reported that atomic Cu anchored on carbon nanosheets showed excellent stability and activity for NITRR. Compared with nanoparticles and bulk materials, Cu single atom exhibited higher adsorption ability of NO₃⁻ and NO₂⁻.

Niu et al. [93] took graphite carbon nitride (g-CN) supported single transition metal atoms as an example and demonstrated the NITRR feasibility of single atom catalyst (SACs) by DFT calculation. Represented by a single transition metal atom catalyst (from Ti to Au) supported by g-CN, the NITRR performance of SACs was studied comprehensively by first principle calculation. The mechanism of transforming NO₃⁻ into NH₃ was summed up as an O-end, O-side, N-end, N-side, and NO-dimer approach. Volcano and contour plots were established to explain the activity trends on the catalysts. The results showed that the high efficiency of NITRR was realized on Ti/g-CN and Zr/g-CN, and the limit potentials were −0.39 and −0.41, respectively. This work provided a way for the application of SACs and lays a foundation for the development of NITRR.