Advancing electrochemical nitrogen reduction: Efficacy of two-dimensional SiP layered structures with single-atom transition metal catalysts

Researchers are interested in single-atom catalysts with atomically scattered metals relishing the enhanced electrocatalytic activity for nitrogen reduction and 100 % metal atom utilization. In this paper, we investigated 18 transition metals (TM) spanning 3d to 5d series as efficient nitrogen reduction reaction (NRR) catalysts on defective 2D SiPV layered structures through first-principles calculation. A systematic screening identified Mo@SiPV, Nb@SiPV, Ta@SiPV and W@SiPV as superior, demonstrating enhanced ammonia synthesis with significantly lower limiting potentials (-0.25, -0.45, -0.49 and -0.15 V, respectively), compared to the benchmark -0.87 eV for the defective SiP. In addition, the descriptor ΔG*N was introduced to establish the relationship between the different NRR intermediates, and the volcano plot of the limiting potentials were determined for their potential-determining steps (PDS). Remarkably, the limiting voltage of the NRR possesses a good linear relationship with the active center TM atom Ɛd, which is a reliable descriptor for predicting the limiting voltage. Furthermore, we verified the stability (using Ab Initio Molecular Dynamics - AIMD) and high selectivity (UL(NRR)-UL(HER) > -0.5 V) of these four catalysts in vacuum and solvent environments. This study systematically demonstrates the strong catalytic potential of 2D TM@SiPV(TM = Mo, Nb, Ta, W) single-atom catalysts for nitrogen reduction electrocatalysis.

Electrochemical nitrogen reduction reaction on anchored SnS2 nanosheets with TM2 dimers

The design of efficient, high-stability nitrogen fixation catalysts remains a great challenge to achieve electrochemical nitrogen reduction reaction (NRR) under ambient conditions. Herein, the high-throughput first-principles calculations are performed to obtain potential electrochemical NRR catalysts from transition metal (TM) dimers anchored on SnS2 nanosheets. The selected W2/SnS2 behaves as a promising NRR candidate possessing -0.27 V limiting potential and 0.81 eV maximum kinetic potential, and it exhibits the adsorption advantages of *N2 over other small molecules (*H2O, *O, *OH, *H). More importantly, the moderate d orbital valence electron number and electronegativity of TM atom could obtain better NRR activity, and a new descriptor φ considering the effects of coordination environments and adsorbates is proposed to achieve the fast pre-screening among various candidates. This work presents practical insights into the fast screening of TM2/SnS2 candidates for efficient nitrogen fixation and further streamlining the design of electrochemical NRR catalysts.

Impact of Vacancy Defects on Electrochemical Nitrogen Reduction Reaction Performance of MXenes

We investigated electrochemical nitrogen reduction reaction (eNRR) on MXenes consisting of the vacancy defects in the functional layer using density functional theory calculations. We considered Mo2 C, W2 C, Mo2 N, and W2 N MXenes with F, N, and O functionalization and investigated distal and alternative associative pathways. We analyzed these MXenes for eNRR based on N2 adsorption energy, NH3 desorption energy, NRR selectivity, and electrochemical limiting potential. While we find that most of the considered MXenes surfaces are more favorable for eNRR compared to hydrogen evolution, these surfaces also have strong NH3 binding (>-1.0 eV) and thus will be covered with NH3 during operating conditions. Amongst all considered MXenes, only W2 NF2 is found to have a low NH3 desorption energy along with low eNRR overpotential and selectivity towards eNRR. The obtained eNRR overpotential and NH3 desorption energy on W2 NF2 are superior to those reported for pristine W2 N3 as well as functionalized MXenes.

A DFT Investigation of B-Doped C3 N as Single Atom Electrocatalysts for N2 -to-NH3 Conversion

The NH3 synthesis from N2 plays an important role in the ecological cycle and industrial production. Different from industrial NH3 synthesis with high pollution and energy consumption, electrocatalytic NH3 synthesis is favored because of its environmental protection, energy saving, ambient reaction conditions and other characteristics. However, due to the low efficiency and poor reaction selectivity of the existing electrocatalysts, which can not be used actually, the development of new electrocatalysts for nitrogen reduction reaction (NRR) is particularly urgent. Herein, we designed a series of transition metal atoms anchored B-doped defective C3 N surface (TM@B2 C3 N) as single-atom catalysts. Through the screening process of N2 adsorption activation, N2 H formation and NH3 desorption, finally the excellent electrocatalysts with strong stability and high activity (Cr@B2 C3 N and Mn@B2 C3 N) were obtained. After simulating the entire pathway, it was found that the NRR process on Cr@B2 C3 N and Mn@B2 C3 N via consecutive and distal pathways with the lowest limiting potential of -0.42 and -0.52 V, which have the good ability to inhibit hydrogen evolution reaction. Finally, the electronic properties were analyzed, and the reason for their high catalytic activity was summarized. This work provides a new idea for the rational design of NRR electrocatalysts and promotes the practical application of electrocatalysts.

Theoretical Insight into the Special Synergy of Bimetallic Site in Co/MoC Catalyst to Promote N2 -to-NH3 Conversion

The catalytic mechanisms of nitrogen reduction reaction (NRR) on the pristine and Co/α-MoC(001) surfaces were explored by density functional theory calculations. The results show that the preferred pathway is that a direct N≡N cleavage occurs first, followed by continuous hydrogenations. The production of second NH3 molecule is identified as the rate-limiting step on both systems with kinetic barriers of 1.5 and 2.0 eV, respectively, indicating that N2 -to-NH3 transformation on bimetallic surface is more likely to occur. The two components of the bimetallic center play different roles during NRR process, in which Co atom does not directly participate in the binding of intermediates, but primarily serves as a reservoir of H atoms. This special synergy makes Co/α-MoC(001) have superior activity for ammonia synthesis. The introduction of Co not only facilitates N2 dissociation, but also accelerates the migration of H atom due to the antibonding characteristic of Co-H bond. This study offers a facile strategy for the rational design and development of efficient catalysts for ammonia synthesis and other reactions involving the hydrogenation processes.

Transition metals anchored on two-dimensional p-BN support with center-coordination scaling relationship descriptor for spontaneous visible-light-driven photocatalytic nitrogen reduction

Solar energy has the potential to revolutionize the production of ammonia, as it could provide a reliable and uninterrupted source of energy for the chemical reaction involved. However, improving the catalytic performance of catalysts often leads to a reduction in their band gaps, which results in insufficient photogenerated electron potential to realize the nitrogen reduction reaction (NRR), and thus the development of NRR efficient photocatalysts remains a great challenge. Herein, based on the density functional theory (DFT), a series of single-atom photocatalysts with transition metals (TMs) doped on porous boron nitride (p-BN) nanosheet are proposed for NRR. Among them, Re-B3@p-BN could effectively catalyze gas-phase N2 through the corresponding pathways with limiting potentials of 0.31 V. Meanwhile, it exhibits excellent light absorption efficiency under illumination and could spontaneously catalyse nitrogen fixation reactions due to the suitable forbidden band and high photogenerated electron potential. Moreover, a linear relationship descriptor based on the intrinsic properties has been established, using a machine learning approach by considering the combined effects of the central metal atom and the coordination atoms. This descriptor could help accelerate the development of rational and improved 2D NRR photocatalysts with high catalytic activity and high selectivity.

Boosting photocatalytic nitrogen reduction reaction by Jahn-Teller effect

Compared with traditional the Haber-Bosch process, photocatalytic ammonia production has attracted a considerable attention due to its advantages of low energy consumption and sustainability. In this work, we mainly study the photocatalytic nitrogen reduction reaction (NRR) on MoO3·0.55H2O and α-MoO3. Structure analysis shows that compared to α-MoO6, the [MoO6] octahedrons in MoO3·0.55H2O obviously distort (Jahn-Teller distortion), leading to the formation of Lewis acid active sites that favors the adsorption and activation of N2. X-ray photoelectron spectroscopy (XPS) further confirms the formation of more Mo5+ as Lewis acid active sites in MoO3·0.55H2O. Transient photocurrent, photoluminescence and electrochemical impedance spectra (EIS) confirmed that MoO3·0.55H2O has a higher charge separation and transfer efficiency than α-MoO3. Density functional theory (DFT) calculation further confirmed that the N2 adsorption on MoO3·0.55H2O is more favorable thermodynamically than that on α-MoO3. As a result, under visible light irradiation (λ ≥ 400 nm) for 60 min, an ammonia production rate of 88.6 μmol·gcat-1 was achieved on MoO3·0.55H2O, which is about 4.6 times higher than that on α-MoO3. In comparison to other photocatalysts, MoO3·0.55H2O exhibits an excellent photocatalytic NRR activity under visible light irradiation without using sacrificial agent. This work offers a new fundamental understanding to photocatalytic NRR from the viewpoint of crystal fine structure, which benefits designing efficient photocatalysts.

The novel π-d conjugated TM2B3N3S6 (TM = Mo, Ti and W) monolayers as highly active single-atom catalysts for electrocatalytic synthesis of ammonia

Recently, single-atom catalysts (SACs) are receiving significant attention in electrocatalysis fields due to their excellent specific activities and extremely high atomic utilization ratio. Effective loading of metal atoms and high stability of SACs increase the number of exposed active sites, thus significantly improving their catalytic efficiency. Herein, we proposed a series (29 in total) of two-dimensional (2D) conjugated structures of TM2B3N3S6 (TM means those 3d to 5d transition metals) and studied the performance as single-atom catalysts for nitrogen reduction reaction (NRR) using density functional theory (DFT). Results show that TM2B3N3S6 (TM = Mo, Ti and W) monolayers have superior performance for ammonia synthesis with low limiting potentials of -0.38, -0.53 and -0.68 V, respectively. Among them, the Mo2B3N3S6 monolayer shows the best catalytic performance of NRR. Meanwhile, the π conjugated B3N3S6 rings undergo coordinated electron transfer with the d orbitals of TM to exhibit good chargeability, and these TM2B3N3S6 monolayers activate isolated N2 according to the "acceptance-donation" mechanism. We have also verified the good stability (i.e., Ef < 0, and Udiss > 0) and high selectivity (Ud = -0.03, 0.01 and 0.10 V, respectively) of the above four types of monolayers for NRR over hydrogen evolution reaction (HER). The NRR activities have been clarified by multiple-level descriptors (ΔG*N2H, ICOHP, and Ɛd) in the terms of basic characteristics, electronic property, and energy. Moreover, the aqueous solution can promote the NRR process, leading to the reduction of ΔGPDS from 0.38 eV to 0.27 eV for the Mo2B3N3S6 monolayer. However, the TM2B3N3S6 (TM = Mo, Ti and W) also showed excellent stability in aqueous phase. This study proves that the π-d conjugated monolayers of TM2B3N3S6 (TM = Mo, Ti and W) as electrocatalysts show great potentials for the nitrogen reduction.

Nanosheet arrays of iron oxide for enhanced ammonia synthesis via electrochemical nitrogen reduction for prospective algal membrane bioreactors

The earth's nitrogen cycle relies on the effective conversion of nitrogen (N2) to ammonia (NH3). As a result, the research and development of catalysts that are earth-abundant, inexpensive, and highly efficient but do not need precious metals is of the utmost significance. In this investigation, we present a controlled synthesis technique to the fabrication of an iron oxide (Fe2O3) nanosheet array by annealing at temperatures ranging from 350 to 550 °C. This array will be used for the electrochemical reduction of atmospheric N2 to NH3 in electrolytes. The Fe2O3 nanosheet array that was produced as a result displays outstanding electrochemical performance as well as remarkable stability. When compared to a hydrogen electrode working under normal temperature and pressure conditions, the Fe2O3 nanosheet array produces an impressive NH3 production rate of 18.04 g per hour per mg of catalytically active material in 0.1 M KOH electrolyte, exhibiting an enhanced Faradaic efficiency (FE) of 13.5% at -0.35 V. This is accomplished by exhibiting an enhanced Faradaic efficiency (FE) of 0.1 M KOH electrolyte. The results of experiments and electrochemical studies reveal that the existence of cation defects in the Fe2O3 nanosheets plays an essential part in the enhancement of the electrocatalytic activity that takes place during nitrogen reduction reactions (NRR). This study not only contributes to the expanding family of transition-metal-based catalysts with increased electrocatalytic activity for NRR, but it also represents a substantial breakthrough in the design of catalysts that are based on transition metals, so it's a win-win. In addition, the use of Fe2O3 nanosheets as electrocatalysts has a lot of potential in algal membrane bioreactors because it makes nitrogen fixation easier, it encourages algae growth, and it makes nitrogen cycling more resource-efficient.

Charge transfer and vacancy engineering of Fe2O3 nanoparticle catalysts for highly selective N2 reduction towards NH3 synthesis

The development of electrocatalysts for N₂ reduction reaction (NRR) is significant for scalable and renewable NH₃ synthesis, but calls for a technology innovation to overcome the specific problems of low efficiency and poor selectivity. Herein, we prepare a core-shell nanostructure by coating polypyrrole (PPy) onto sulfur-doped iron oxide nanoparticles (denoted as S-Fe₂O₃@PPy) as the highly selective and durable electrocatalysts for NRR under ambient conditions. Sulfur doping and PPy coating remarkably improve the charge transfer efficiency of S-Fe₂O₃@PPy, and the interactions between PPy and Fe₂O₃ nanoparticles produce abundant oxygen vacancies as active sites for NRR. This catalyst achieves an NH₃ production rate of 22.1 μg h^-1 mg_cat^-1 and a very-high Faradic efficiency of 24.6%, surpassing other Fe₂O₃ based NRR catalysts. Density functional theory calculations show that the S-coordinated iron site can successfully activate the N₂ molecule and optimize the energy barrier during the reduction process, resulting in a small theoretical limiting potential.

Vanadium oxide, Vanadium Oxynitride, and Cobalt Oxynitride as Electrocatalysts for the Nitrogen Reduction Reaction: A Review of Recent Developments

The electrocatalytic reduction of molecular nitrogen to ammonia-the nitrogen reduction reaction (NRR)-is of broad interest as an environmentally- and energy-friendly alternative to the Haber-Bosch process for agricultural and emerging energy applications. Herein, we review our recent findings from collaborative electrochemistry/surface science/theoretical studies that counter several commonly held assumptions regarding transition metal oxynitrides and oxides as NRR catalysts. Specifically, we find that for the vanadium oxide, vanadium oxynitride, and cobalt oxynitride systems, (a) there is no Mars-van Krevelen mechanism and that the reduction of lattice nitrogen and N2 to NH3 occurs by parallel reaction mechanisms at O-ligated metal sites without incorporation of N into the oxide lattice; and (b) that NRR and the hydrogen evolution reaction (HER) do occur in concert under the conditions studied for Co oxynitride, but not for V oxynitride. Additionally, these results highlight the importance of both O-ligation of the V or Co center for metal-binding of dinitrogen, and the importance of N in stabilizing the transition metal cation in an intermediate oxidation state, for effective N≡N bond activation. This review also highlights the importance and limitations of ex situ and in situ photoemission-involving controlled transfer between UHV and electrochemistry environments, and of operando Near Ambient Pressure photoemission coupled with in situ studies, in elucidating the complex chemistry relevant to the electrolyte/solid interface.&#xD.

Oxygen Functionalization-Induced Charging Effect on Boron Active Sites for High-Yield Electrocatalytic NH3 Production

Ammonia has been recognized as the future renewable energy fuel because of its wide-ranging applications in H₂ storage and transportation sector. In order to avoid the environmentally hazardous Haber-Bosch process, recently, the third-generation ambient ammonia synthesis has drawn phenomenal attention and thus tremendous efforts are devoted to developing efficient electrocatalysts that would circumvent the bottlenecks of the electrochemical nitrogen reduction reaction (NRR) like competitive hydrogen evolution reaction, poor selectivity of N₂ on catalyst surface. Herein, we report the synthesis of an oxygen-functionalized boron carbonitride matrix via a two-step pyrolysis technique. The conductive BNCO₍₁₀₀₀₎ architecture, the compatibility of B-2p_z orbital with the N-2p_z orbital and the charging effect over B due to the C and O edge-atoms in a pentagon altogether facilitate N₂ adsorption on the B edge-active sites. The optimum electrolyte acidity with 0.1 M HCl and the lowered anion crowding effect aid the protonation steps of NRR via an associative alternating pathway, which gives a sufficiently high yield of ammonia (211.5 μg h^-1 mg_cat^-1) on the optimized BNCO₍₁₀₀₀₎ catalyst with a Faradaic efficiency of 34.7% at - 0.1 V vs RHE. This work thus offers a cost-effective electrode material and provides a contemporary idea about reinforcing the charging effect over the secured active sites for NRR by selectively choosing the electrolyte anions and functionalizing the active edges of the BNCO₍₁₀₀₀₎ catalyst.

Regulating the spin state of single-atom doped covalent triazine frameworks for efficient nitrogen fixation

Covalent triazine frameworks (CTFs), served as a versatile platform, can form expedient metal-N single-atom coordination sites as promising catalytic centers. To seek out excellent candidate catalysts of M/CTFs (M = Transition metal) for nitrogen reduction reaction (NRR), a "five-step" strategy involving spin states has been established for hierarchical high-throughput screening and reveals strong coordination ability of the CTFs, outstanding conductivity of the M/CTFs, effective adsorption and activation of N₂* attributed to the electron transfer and orbital hybridization between the M/CTFs and N₂*. Among the potential candidates, the Cr/CTF is screened out to be an excellent one for nitrogen fixation, which can not only inhibit hydrogen evolution reaction (HER) greatly but also has good thermodynamic stability (E_b =  -4.40 eV), narrow band gap (E_g = 0.03 eV), moderate adsorption energy (E_a =  -0.84 eV), large activation energy (ΔG_N2* = -0.71 eV) and a theoretical Faradaic efficiency of 100%. The spin state has been confirmed to be an important descriptor of catalytic activity and the two-state reactivity (TSR) is validated to exist in the NRR. Reaction mechanism with different spin states of Cr/CTF has been demonstrated to give a great impact on the nitrogen fixation, providing solid theoretical support for the design of more efficient NRR catalysts.

Water-Phase Lateral Interconnecting Quantum Dots as Free-Floating 2D Film Assembled by Hydrogen-Bonding Interactions to Acquire Excellent Electrocatalytic Activity

Supramolecular self-assembly of nanoparticles in two orthogonal directions would potentially allow one to fabricate nanomaterials with fascinating properties. In this study of a hydrothermal polycondensation of melamine/cyanuric acid, graphitic carbon nitride-based quantum dots (CNQD, ∼2 nm) are in situ arranged along two orthogonal directions through lateral hydrogen bonding, and free-floating two-dimensional hydrogen-bonded films of CNQD (2D CNQD) are built. On the basis of the universality of this hydrothermal in situ supramolecular self-assembly technique, 2D films linked by other quantum dots such as sulfur-doped graphitic carbon nitride and CdTe are also constructed. With the benefits of stimuli responsiveness and the reversibility of hydrogen bonds, controllable assembly/disassembly of the 2D CNQD film is feasibly achieved by external stimuli such as inletting CO₂/N₂, which endows the assembled 2D CNQD films optimal electrochemical superiorities of both 2D film and zero-dimensional (0D) quantum dots. Accordingly, the 2D CNQD film delivers a high bifunctional activity in both a nitrogen reduction reaction (NRR) and an oxygen evolution reaction (OER). Especially in NRR, it exhibits the high yield rate of NH₃ reaching 75.07 μg h^-1 mg^-1 at -0.85 V versus reversible hydrogen electrode at ambient condition. Strikingly, the power density of the rechargeable Zn-N₂ battery using 2D CNQD film as cathode reaches 31.94 mW cm^-2, outperforming the majority of Zn-N₂ batteries. Density functional theory calculations proved the promoted adsorption of N₂ and stabilized NRR intermediates on 2D CNQD cooperated by multiply hydrogen-bonding interactions are the main reasons for the excellent NRR electrocatalytic performances. This work hints that hydrothermal in situ supramolecular self-assembly is a feasible and direct way to integrate 0D quantum dots into 2D directional arrays, and the hydrogen bond that interlinks enables this free-floating 2D structure to maintain the electrochemical superiority of both 0D and 2D structures.

Photocatalytic and photo-electrochemical ammonia synthesis over dimensional oriented cobalt titanate/nitrogen-doped reduced graphene oxide junction interface catalyst

Nitrogen reduction to ammonia is vital for chemical industries and renewable clean energy. Denying the harsh reaction conditions adopted in the Haber-Bosch process and stimulation research for ammonia production through sustainable technologies is a smart approach. Hitherto, photocatalyst acquiring the potential to attain high nitrogen reduction reaction (NRR) efficiency is a challenging task. Here, this study demonstrated cobalt titanate (CoTiO₃) rods (p-type) straddled with two-dimensional (2D) sheets of nitrogen-doped reduced graphene oxide (N-rGO, n-type) via, reflux method; realizing the advantages of dissimilar dimensionalities and strong interfacial junction coupling for efficient NRR under visible light irradiation. The successful interface junction establishment between CoTiO₃ and N-rGO has been witnessed from Raman, x-ray photoelectron spectroscopy (XPS), and Mott-Schottky analysis. Moreover, a well-defined type-II band structure is capable to curl the charge anti-recombination process; reflected in upgraded photo-catalytic/electrocatalytic upshots. The CoTiO₃ modified with an optimized concentration of N-rGO exhibits high stability with an improved photocatalytic (1722.22 μmolL^-1h^-1) and photo-electrocatalytic (16.8 µg cm^-1h^-1) nitrogen reduction to ammonia production; multiple times higher than counterparts. This improved photo-activity of CoTiO₃/N-rGO junction hybrid stems from the built-in electric field existing across the dissimilar junction interface, triggering charge transfer channels for reduction reaction in mild reaction conditions. The result of these materials might strategies the way for future development of new functionalities bearing highly active catalyst materials for sustainable energy-related conversion.

Ball milling transformed electroplating sludges with different components to spinels for stable electrocatalytic ammonia production under ambient conditions

Electroplating sludge is classified as hazardous waste, but it is also a potential raw resource since it contains plenty of transition metals. However, the component of electroplating sludge is unstable, which hinders recycling. This work investigates the possibility to synthesize spinels with stable catalytic performances by different electroplating sludges. The obtained catalysts are used in electrocatalytic N₂ reduction to produce ammonia. As a result, CuCr₂O₄, ZnCr₂O₄, and NiCr₂O₄ spinels are successfully synthesized by a ball-milling and calcination method. These spinels result in ammonia yields of 7.30-8.86 μg h^-1 mg^-1_cat. Among the three spinels, CuCr₂O₄ shows the highest yield of 8.86 μg h^-1 mg^-1_cat at -0.9 V. Its faradaic efficiency reaches 0.57%. In addition, no by-product N₂H₄ is detected, indicating a high selectivity. The catalytic process is carried out by both distal and alternating pathways, in which metal doping and oxygen vacancy function as binding sites for N₂ adsorption and reduction. Above results indicate that electroplating sludges with unstable components are feasible to produce spinels for stable electrocatalytic ammonia production under ambient temperature. This is in favor of high-value-added utilization of hazardous waste, and devotes to circular economy.

Hierarchical CoS2/MoS2 flower-like heterostructured arrays derived from polyoxometalates for efficient electrocatalytic nitrogen reduction under ambient conditions

Electrochemical nitrogen reduction reaction (NRR) has been identified as a prospective alternative for sustainable ammonia production. Developing cost-effective and highly efficient electrocatalysts is critical for NRR under ambient conditions. Herein, the hierarchical cobalt-molybdenum bimetallic sulfide (CoS₂/MoS₂) flower-like heterostructure assembled from well-aligned nanosheets has been easily fabricated through a one-step strategy. The efficient synergy between different components and the formation of heterostructure in CoS₂/MoS₂ nanosheets with abundant active sites makes the non-noble metal catalyst CoS₂/MoS₂ highly effective in NRR, with a high NH₃ yield rate (38.61 μg h^-1 mg_cat.^-1), Faradaic efficiency (34.66%), high selectivity (no formation of hydrazine) and excellent long-term stability in 1.0 mol L^-1 K₂SO₄ electrolyte (pH = 3.5) at -0.25 V versus the reversible hydrogen electrode (vs. RHE) under ambient conditions, exceeding much recently reported cobalt- and molybdenum-based materials, even catch up with some noble-metal-based catalyst. Density functional theory (DFT) calculation indicates that the formation of N₂H* species on CoS₂(200)/MoS₂(002) is the rate-determining step via both the alternating and distal pathways with the maximum ΔG values (1.35 eV). These results open up opportunities for the development of efficient non-precious bimetal-based catalysts for NRR.

Computational screening of highly selective and active electrocatalytic nitrogen reduction on single-atom-embedded artificial holey SnN3 monolayers

Billowy interest during nitrogen reduction reaction (NRR) for single-atom catalysts (SACs) has been evoked by the discovery of single transition metal (TM) atom structures featured by TM-N_x coordinate sites as an excellent catalytic center. However, a great challenge of currently available SACs, far away from industrial requirement, is the low activity and poor selectivity. Therefore, in NRR, the first-principles high-throughput screening calculations were performed to evaluate the feasibility of a single TM atom (from Sc to Au) embedded an artificial holey defective SnN₃ (d-SnN₃) monolayer. Here, all TM atoms can be stably anchored on d-SnN₃ (TM/d-SnN₃), meanwhile, most of adsorbed N₂ molecules can be favorably activated via the "σ donation - π* back-donation" interaction. Eventually, among 27 TM centers, V, Mo, Hf and Ta/d-SnN₃ stand out because of extremely low limiting potential (-0.21, -0.40, -0.56 and -0.54 V, respectively), lower than majority of TM-based NRR catalysts and far below that of the Ru (0001) surface (0.98 V), indicative of fast kinetics and low energy cost of NRR. Moreover, their intrinsic characteristic, such as centralized spin-polarization on these TM atoms, high-efficient prohibition of the competitive hydrogen evolution reaction is responsible for high selectivity with theoretical faradic efficiency of 100%. Also, multiple-level descriptors including ΔG_∗N, ICOHP, and Φ were used to make the source of NRR activity clear, realizing an efficient and quick prescreening among different candidates. Particularly, their excellent durability, kinetic stability and synthetic accessibility guarantee the feasibility in real experimental conditions.

Superaerophobic copper-based nanowires array for efficient nitrogen reduction

Electrocatalytic N₂ reduction reaction (NRR) provides a promising route for NH₃ production under ambient conditions to replace traditional Haber-Bosch process. For this purpose, efficient NRR electrocatalysts with high NH₃ yield rate and high Faradaic efficiency (FE) are required. Cu-based materials have been recognized catalytic active for some multi-electron-involved reduction reactions and usually exhibit inferior catalytic activities for hydrogen evolution reaction. We report here the preparation and characterization of a series of Cu-based nanowires array (NA) catalysts in situ grown on Cu foam (CF) substrate, including Cu(OH)₂ NA/CF, Cu₃N NA/CF, Cu₃P NA/CF, CuO NA/CF and Cu NA/CF, which are directly used as self-supported catalytic electrodes for NRR. The electrochemical results show that CuO NA/CF achieves a highest NH₃ yield rate of 1.84 × 10^-9 mol s^-1 cm^-2, whereas Cu NA/CF possesses a highest FE of 18.2% for NH₃ production at -0.1 V versus reversible hydrogen electrode in 0.1 M Na₂SO₄. Such catalytic performances are superior to most of recently reported metal-based NRR electrocatalysts. The contact angle measurements and the simulated calculations are carried out to reveal the important role of the superaerophobic NA surface structure for efficient NRR electrocatalysis.

Electrocatalytic performance of Sb-modified Bi25FeO40 for nitrogen fixation

The Haber-Bosch N₂ fixation method suffers from the power-consuming and harsh conditions. In contrast, the electrochemical conversion of N₂ (NRR) at room temperature and atmospheric pressure is considered a promising alternative route. In this study, we synthesized Sb-modified with Bi₂₅FeO₄₀ (BFSO/BFO) by using one-step hydrothermal treatment. The BFSO/BFO catalyst has higher selectivity to NRR than Bi₂₅FeO₄₀ (BFO) under the same applied voltage. Such large interfacial interaction area plays a critical role in transfer electron and enhances the density of current. The resulting BFSO/BFO heterojunction showed significant electrocatalytic activity under controllable voltage, which exhibited favorable average ammonia (NH₃) yield as high as 2.62 μg·h^-1·cm^-2 at -0.2 V versus RHE. Moreover, the stability of the BFSO/BFO composite was evaluated for six cycles and the results were desirable. This study provides a new insight into the design of composite catalysts using BFO, which has high activity and selectivity toward NRR.

Ag (111) surface for ambient electrolysis of nitrogen to ammonia

In this paper, the reaction process of N₂ convert to NH₃ catalyzed by Ag (111) surface was obtained through the construction of Ag (111) surface and computational simulation. The charge transfer in the reaction process and the change of N≡N bond length are described. Since the N₂ reduction reaction (NRR) usually occurs under alkaline solution conditions, we calculated and described the coexistence of OH* and N₂. At the same time, the co-adsorption structure of OH* and N₂ at different adsorption sites was studied.

Metal-Free B@g-CN: Visible/Infrared Light-Driven Single Atom Photocatalyst Enables Spontaneous Dinitrogen Reduction to Ammonia

Conversion of naturally abundant dinitrogen (N₂) to ammonia (NH₃) is one of the most attractive and challenging topics in chemistry. Current studies mainly focus on electrocatalytic nitrogen reduction reaction (NRR) using metal-based electrocatalysts, while metal-free and solar-driven photocatalysts have been rarely explored. Here, on the basis of the "σ donation-π* back-donation" concept, single B atom supported on holey g-CN (B@g-CN) can serve as metal-free photocatalyst for highly efficient N₂ fixation and reduction under visible and even infrared spectra. Our results reveal that N₂ can be efficiently activated and reduced to NH₃ with extremely low overpotential of 0.15 V and activation barrier of 0.61 eV, lower than most of metal-based NRR catalysts, thereby guaranteeing low energy cost and fast kinetics of NRR. The inherent properties of B@g-CN, such as centralized spin-polarization on the B atom, efficient prohibition of competitive hydrogen evolution reaction (HER), and reduced exciton binding energy, are responsible for the high selectivity and Faradaic efficiency for NRR under ambient conditions. Moreover, for the first time, we theoretically disclose that the external potential provided by photogenerated electrons for NRR/HER endowing B@g-CN spontaneous NRR and inaccessible HER. This work may provide a promising lead for designing efficient and robust metal-free single atom catalysts toward photocatalytic NRR under visible/infrared spectrum.