Tackling the Activity and Selectivity Challenges of Electrocatalysts toward the Nitrogen Reduction Reaction via Atomically Dispersed Biatom Catalysts

Rational Synthesis and Regulation of Hollow Structural Materials for Electrocatalytic Nitrogen Reduction Reaction

The electrocatalytic nitrogen reduction reaction (NRR) is known as a promising mean of nitrogen fixation to mitigate the energy crisis and facilitate fertilizer production under mild circumstances. For electrocatalytic reactions, the design of efficient catalysts is conducive to reducing activation energy and accelerating lethargic dynamics. Among them, hollow structural materials possess cavities in their structures, which can slack off the escape rate of N2 and reaction intermediates, prolong the residence time of N2 , enrich the reaction intermediates' concentration, and shorten electron transportation path, thereby further enhancing their NRR activity. Here, the basic synthetic strategies of hollow structural materials are introduced first. Then, the recent breakthroughs in hollow structural materials as NRR catalysts are reviewed from the perspective of intrinsic, mesoscopic, and microscopic regulations, aiming to discuss how structures affect and improve the catalytic performance. Finally, the future research directions of hollow structural materials as NRR catalysts are discussed. This review is expected to provide an outlook for optimizing hollow structural NRR catalysts.

Reduction of N2 to NH3 catalyzed by a Keggin-type polyoxometalate-supported dual-atom catalyst

In the present paper, a polyoxometalate-supported dual-atom catalyst has been designed for the nitrogen reduction reaction based on our density functional theory calculations.

Descriptors and graphical construction for in silico design of efficient and selective single atom catalysts for the eNRR

Outline a screening protocol that uses density functional theory calculations to simultaneously optimize with respect to multiple criteria, thereby successfully identifying catalysts that are highly selective and also result in low overpotentials for ammonia production through eNRR.

Tantalum based single, double, and triple atom catalysts supported on g-C2N monolayer for effective nitrogen reduction reaction: a comparative DFT investigation

Density functional theory simulations demonstrate that single and triple Ta-atom catalysts anchored to C2N monolayer act as superior catalysts for the nitrogen reduction reaction via alternating and distal pathways.

Mixture screening strategy of efficient transition metal heteronuclear dual-atom electrocatalysts toward nitrogen fixation

A simple mixture screening strategy is proposed to rapidly evaluate the NRR activity of M1M2-NC. VRu-NC exhibits a high NRR activity (UL = −0.21 V) and suppression of the competitive HER following the mixed mechanism.

Multi-atom cluster catalysts for efficient electrocatalysis

This review presents recent developments in the synthesis, modulation and characterization of multi-atom cluster catalysts for electrochemical energy applications.

Performance of Nitrogen Reduction Reaction on Metal Bound g-C6N6: Combined Approach of Machine Learning and DFT

Developing a cost-effective and environmentally benign substitute for the energy-intensive Haber-Bosch process for the production of ammonia is a global challenge. Electrocatalytic nitrogen reduction reaction (NRR) under ambient condition through...

Non-metal boron atoms on a CuB12 monolayer as efficient catalytic sites for urea production

Non-metal B atoms at the midpoint of the edges of the squares is confirmed to be the excellent catalytic sites on CuB12 monolayer presents superior catalytic activity thermodynamically and kinetically than the reported urea catalysts.

In situ modification of d-band in core-shell structure for efficient hydrogen storage via electrocatalytic N2 fixation

The electrochemical N₂ reduction reaction (NRR) into NH₃, especially powered by clean and renewable electricity, is a promising alternative to the capital- and energy-intensive Haber–Bosch process. However, the inert N Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> N bond and the frantic competition of the hydrogen evolution reaction lead to a poor NH₃ yield rate and faradaic efficiency (FE). Here, we in situ construct a series of two-dimension core/shell V₂O₃/VN nanomeshes with a gradient nitride-layer thickness. Among them, V₂O₃/VN-2 exhibits the highest FE of 34.9%, an excellent NH₃ yield rate of 59.7 μg h⁻¹ mg_cat.⁻¹, and outstanding cycle stability, exceeding those of most of the NRR electrocatalysts reported to date. First-principles calculations reveal that the d-band center of VN shifts up in a nearly linear manner with the decrease of nitride-layer thickness, and V₂O₃/VN-2 with a d-band center closer to the Fermi level can strengthen the d–2π* coupling between the catalyst and N₂ molecule, notably facilitating the N₂-into-NH₃ conversion.

In 2D core/shell V₂O₃/VN nanomeshes with a gradient nitride-layer thickness, the V₂O₃ core can tune the d-band structure of the VN shell, strengthen the interaction between N₂ and the active site, and thus enhance electrochemical NRR performance.

Double metal synergistic synthetic urea: an electrocatalytic study

Urea was synthesized from CO2 and N2 electrocatalyzed by doping V and M on an –N–C substrate.

The reduction reaction of carbon dioxide on a precise number of Fe atoms anchored on two-dimensional biphenylene

The reduction reaction of carbon dioxide on a precise number of Fe atoms anchored on two-dimensional biphenylene.

Atomically Dispersed Cu Anchored on Nitrogen and Boron Codoped Carbon Nanosheets for Enhancing Catalytic Performance

Development of high-performance heterogeneous catalytic materials is important for the rapid upgrade of chemicals, which remains a challenge. Here, the benzene oxidation reaction was used to demonstrate the effectiveness of the atomic interface strategy to improve catalytic performance. The developed B,N-cocoordinated Cu single atoms anchored on carbon nanosheets (Cu₁/B-N) with the Cu-N₂B₁ atomic interface was prepared by the pyrolysis of a precoordinated Cu precursor. Benefiting from the unique atomic Cu-N₂B₁ interfacial structure, the designed Cu₁/B-N exhibited considerable activity in the oxidation of benzene, which was much higher than Cu₁/N-C, Cu NPs/N-C, and N-C catalysts. A theoretical study showed that the enhanced catalytic performance resulted from the optimized adsorption of intermediates, which originated from the manipulation of the electronic structure of Cu single atoms induced by B atom coordination in the Cu-N₂B₁ atomic interface. This study provides an innovative approach for the rational design of high-performance heterogeneous catalytic materials at the atomic level.

Improving the Activity of Electrocatalysts toward the Hydrogen Evolution Reaction, the Oxygen Evolution Reaction, and the Oxygen Reduction Reaction via Modification of Metal and Ligand of Conductive Two-Dimensional Metal-Organic Frameworks

Exploring efficient and stable electrocatalysts for the hydrogen evolution reaction (HER) and the oxygen evolution and reduction reactions (OER and ORR) is vital to the development of renewable energy technologies. Herein, on the basis of density functional theory (DFT) calculations, we systematically investigated 30 TMN_xO_4-x-HTP (TM = Fe, Co, Ni, Ru, Rh and Pd; x = 0-4; HTP refers to hexatriphenylene) analogs of conductive two-dimensional (2D) metal-organic frameworks (MOFs) as potential catalysts for HER, OER, and ORR. The results show the good stabilities and metallic features of TMN_xO_4-x-HTP. The interaction strength between intermediates and catalysts governs the catalytic activities, which can be modulated by tuning the TM atom and the local coordination number of N/O in catalysts. RhN₃O₁-HTP is an efficient bifunctional catalyst for HER and OER, and RhN₁O₃-HTP is a promising bifunctional catalyst for OER and ORR. Our findings highlight a potentially efficient class of electrocatalysts based on 2D MOF materials.

Transition Metal-Modified Co4 Clusters Supported on Graphdiyne as an Effective Nitrogen Reduction Reaction Electrocatalyst

Conversion of N₂ into NH₃ through the electrochemical nitrogen reduction reaction (NRR) under ambient conditions represents a novel green ammonia synthesis method. The main obstacle for NRR is lack of efficient, stable, and cost-effective catalysts. In this work, by using density functional theory calculations, 16 transition metal-modified Co₄ clusters supported on graphdiyne (GDY) as potential NRR catalysts were systematically screened. Through the examinations of stability, N₂ activation, selectivity, and activity, Ti-, V-, Cr-, Mn-, and Zr-Co₃@GDY were identified as the promising candidates toward NRR. Further explorations on the NRR mechanisms and the Pourbaix diagrams suggest that Ti-Co₃@GDY was the most promising candidate catalyst, as it has the lowest limiting potential and high stability under the working conditions. The high activities originate from the synergy effect, where the Co₃ cluster acts as the electron donor and the heteroatom serves as the single active site throughout the NRR process. Our results offer a new perspective for advancing sustainable NH₃ production.

Boosting the Electrocatalytic Conversion of Nitrogen to Ammonia on Metal-Phthalocyanine-Based Two-Dimensional Conjugated Covalent Organic Frameworks

The electrochemical N₂ reduction reaction (NRR) under ambient conditions is attractive in replacing the current Haber-Bosch process toward sustainable ammonia production. Metal-heteroatom-doped carbon-rich materials have emerged as the most promising NRR electrocatalysts. However, simultaneously boosting their NRR activity and selectivity remains a grand challenge, while the principle for precisely tailoring the active sites has been elusive. Herein, we report the first case of crystalline two-dimensional conjugated covalent organic frameworks (2D c-COFs) incorporated with M-N₄-C centers as novel, defined, and effective catalysts, achieving simultaneously enhanced activity and selectivity of electrocatalytic NRR to ammonia. Such 2D c-COFs are synthesized based on metal-phthalocyanine (M = Fe, Co, Ni, Mn, Zn, and Cu) and pyrene units bonded by pyrazine linkages. Significantly, the 2D c-COFs with Fe-N₄-C center exhibit higher ammonia yield rate (33.6 μg h^-1 mg_cat^-1) and Faradaic efficiency (FE, 31.9%) at -0.1 V vs reversible hydrogen electrode than those with other M-N₄-C centers, making them among the best NRR electrocatalysts (yield rate >30 μg h^-1 mg_cat^-1 and FE > 30%). In situ X-ray absorption spectroscopy, Raman spectroelectrochemistry, and theoretical calculations unveil that Fe-N₄-C centers act as catalytic sites. They show a unique electronic structure with localized electronic states at Fermi level, allowing for stronger interaction with N₂ and thus faster N₂ activation and NRR kinetics than other M-N₄-C centers. Our work opens the possibility of developing metal-nitrogen-doped carbon-rich 2D c-COFs as superior NRR electrocatalyst and provides an atomic understanding of the NRR process on M-N_x-C based electrocatalysts for designing high-performance NRR catalysts.

Electrochemical Ammonia Synthesis via NO Reduction on 2D-MOF

Developing new catalysts, which effectively promote electrocatalytic NO reduction (ENOR), is very important for the industrial field. A two-dimensional (2D) metal-organic framework (MOF) with hexaaminobenzene (HAB) ligands (TM-HAB MOF, TM = Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Ru, Rh and Pd) as an electrocatalyst of ENOR has been systematically explored in this work by means of well-defined density functional theory (DFT) calculations. We predicted the impacts of the coordination structure of different MOFs on its catalytic performance, and found that the suitable candidates are the Co- and Rh-HAB MOFs due to moderate binding strength between NO and substrates. The further calculation indicated that Co-HAB MOF has the best ENOR catalytic activity with a limiting potential of -0.26 V toward NH 3 product at low NO coverage, yet NO reduction to N 2 O at high NO coverage has been limited due to high limiting potential. The scaling relationship with a good correlation coefficient between several electronic properties and the adsorption Gibbs free energy change of *NO (ΔG *NO ) were found, which implied that ΔG *NO can be used as a simple descriptor for screening out suitable electrocatalysts. This work offers a new paradigm for ENOR toward NH 3 under ambient conditions.

Facile N≡N Bond Cleavage by Anionic Trimetallic Clusters V3-x Tax C4 - (x=0-3): A DFT Study

Activation of N₂ on anionic trimetallic V_3-x Ta_x C₄ ^- (x=0-3) clusters was theoretically studied employing density functional theory. For all studied clusters, initial adsorption of N₂ (end-on) on one of the metal atoms (denoted as Site 1) is transferred to an of end-on: side-on: side-on coordination on three metal atoms, prior to N₂ dissociation. The whole reaction is exothermic and has no global energy barriers, indicating that the dissociation of N₂ is facile under mild conditions. The reaction process can be divided into two processes: N₂ transfer (TRF) and N-N dissociation (DIS). For V-series clusters, which has a V atom on Site 1, the rate-determining step is DIS, while for Ta-series clusters with a Ta on Site 1, TRF may be the rate-determining step or has energy barriers similar to those of DIS. The overall energy barriers for heteronuclear V₂ TaC₄ ^- and VTa₂ C₄ ^- clusters are lower than those for homonuclear V₃ C₄ ^- and Ta₃ C₄ ^- , showing that the doping effect is beneficial for the activation and dissociation of N₂ . In particular, V-Ta₂ C₄ ^- has low energy barriers in both TRF and DIS, and it has the highest N₂ adsorption energy and a high reaction heat release. Therefore, a trimetallic heteronuclear V-series cluster, V-Ta₂ C₄ ^- , is suggested to have high reactivity to N₂ activation, and may serve as a prototype for designing related catalysts at a molecular level.

Rational Design of Graphene Derivatives for Electrochemical Reduction of Nitrogen to Ammonia

The conversion of nitrogen to ammonia offers a sustainable and environmentally friendly approach for producing precursors for fertilizers and efficient energy carriers. Owing to the large energy density and significant gravimetric hydrogen content, NH₃ is considered an apt next-generation energy carrier and liquid fuel. However, the low conversion efficiency and slow production of ammonia through the nitrogen reduction reaction (NRR) are currently bottlenecks, making it an unviable alternative to the traditional Haber-Bosch process for ammonia production. The rational design and engineering of catalysts (both photo- and electro-) represent a crucial challenge for improving the efficiency and exploiting the full capability of the NRR. In the present review, we highlight recent progress in the development of graphene-based systems and graphene derivatives as catalysts for the NRR. Initially, the history, fundamental mechanism, and importance of the NRR to produce ammonia are briefly discussed. We also outline how surface functionalization, defects, and hybrid structures (single-atom/multiatom as well as composites) affect the N₂ conversion efficiency. The potential of graphene and graphene derivatives as NRR catalysts is highlighted using pertinent examples from theoretical simulations as well as machine learning based performance predictive methods. The review is concluded by identifying the crucial advantages, drawbacks, and challenges associated with principal scientific and technological breakthroughs in ambient catalytic NRR.

Two-Dimensional Defective Boron-Doped Niobic Acid Nanosheets for Robust Nitrogen Photofixation

Direct nitrogen photofixation is a feasible solution toward sustainable production of ammonia under mild conditions. However, the generation of active sites for solar-dirven nitrogen fixation not only limits the fundamental understanding of the relationship among light absorption, charge transfer, and catalytic efficiency but also influences the photocatalytic activity. Herein, we report two-dimensional boron-doped niobic acid nanosheets with oxygen vacancies (B-V_o-HNbO₃ NSs) for efficient N₂ photofixation in the absence of any scavengers and cocatalysts. Impressively, B-V_o-HNbO₃ NS as a model catalyst achieves the enhanced ammonia evolution rate of 170 μmol g_cat^-1 h^-1 in pure water under visible-light irradiation. The doublet coupling representing ¹⁵NH₄⁺ in an isotopic labeling experiment and in situ infrared spectra confirm the reliable ammonia generation. The experimental analysis and density functional theory (DFT) calculations indicate that the strong synergy of boron dopant and oxygen vacancy regulates band structure of niobic acid, facilitates photogenerated charge transfer, reduces free energy barriers, accelerates reaction kinetics, and promotes the high rates of ammonia evolution. This work provides a general strategy to design active photocatalysts toward solar N₂ conversion.

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.

Computational Screening of High Activity and Selectivity TM/g-C3N4 Single-Atom Catalysts for Electrocatalytic Reduction of Nitrates to Ammonia

Electrocatalytic reduction of nitrates (NO₃RR) selectively generating ammonia (NH₃) opens up a new idea for treating nitrates in wastewater, which not only reduces nitrates but also obtains the valuable product ammonia. By first-principles calculations, we explore the activity and selectivity for NO₃RR to NH₃ of TM/g-C₃N₄ single-atom catalysts. Six TM/g-C₃N₄ catalysts (TM = Ti, Os, Ru, Cr, Mn, and Pt) are selected by a four-step screening method. Ru/g-C₃N₄ is the most promising of these six TM/g-C₃N₄ catalysts because of its lowest energy barrier and extraordinary selectivity. The origin of the NO₃RR activity of Ru/g-C₃N₄ is explained from the viewpoint of NO₃^- adsorption. In addition, the hydrogen evolution reaction has also been implied to be uncompetitive for the poor adsorption on H atoms. This work provides a screening mechanism for finding new catalysts for NO₃RR to NH₃, promotes the development of NO₃RR, and provides a stimulating impetus for further experimental exploration.

Plasmon-Boosted Cu-Doped TiO2 Oxygen Vacancy-Rich Luminol Electrochemiluminescence for Highly Sensitive Detection of Alkaline Phosphatase

In this study, an effective oxygen vacancy (O_v)-involved luminol-dissolved oxygen (O₂) electrochemiluminescence (luminol-DO ECL) system was developed and exploited for ECL sensing applications through significant plasmon enhancement of the O_v-involved weak luminol-DO ECL signals by the combined use of Cu-doped TiO₂ oxygen vacancy and a Au@SiO₂ nanomembrane. The results disclosed that the ECL response of the corresponding system could be synergistically boosted, and the plausible underlying mechanism has been discussed. Furthermore, for the first time, the developed system has been successfully applied for the highly sensitive detection of alkaline phosphatase with a low limit of detection of 0.005 U/L, with an excellent linear range from 0.005 to 10 U/L, as well as good stability and reproducibility.

Emerging two-dimensional nanomaterials for electrochemical nitrogen reduction

Ammonia (NH₃) is essential to serve as the biological building blocks for maintaining organism function, and as the indispensable nitrogenous fertilizers for increasing the yield of nutritious crops. The current Haber-Bosch process for industrial NH₃ production is highly energy- and capital-intensive. In light of this, the electroreduction of nitrogen (N₂) into valuable NH₃, as an alternative, offers a sustainable pathway for the Haber-Bosch transition, because it utilizes renewable electricity and operates under ambient conditions. Identifying highly efficient electrocatalysts remains the priority in the electrochemical nitrogen reduction reaction (NRR), marking superior selectivity, activity, and stability. Two-dimensional (2D) nanomaterials with sufficient exposed active sites, high specific surface area, good conductivity, rich surface defects, and easily tunable electronic properties hold great promise for the adsorption and activation of nitrogen towards sustainable NRR. Therefore, this Review focuses on the fundamental principles and the key metrics being pursued in NRR. Based on the fundamental understanding, the recent efforts devoted to engineering protocols for constructing 2D electrocatalysts towards NRR are presented. Then, the state-of-the-art 2D electrocatalysts for N₂ reduction to NH₃ are summarized, aiming at providing a comprehensive overview of the structure-performance relationships of 2D electrocatalysts towards NRR. Finally, we propose the challenges and future outlook in this prospective area.

Recent Advances and Perspective on Electrochemical Ammonia Synthesis under Ambient Conditions

Ammonia is an essential chemical for agriculture and industry. To date, NH₃ is mainly supplied by the traditional Haber-Bosch process, which is operated under high-temperature and high-pressure in a centralized way. To achieve ammonia production in an environmentally benign way, electrochemical NH₃ synthesis under ambient conditions has become the frontier of energy and chemical conversion schemes, as it can be powered by renewable energy and operates in a decentralized way. The recent progress on developing different strategies for NH₃ production, including 1) classic NH₃ synthesis pathways over nanomaterials; 2) the Mars-van Krevelen (MvK) mechanism over metal nitrides (MN_x ); 3) reducing the nitrate into NH₃ over Cu-based nanomaterial; and 4) metal-N₂ battery release of NH₃ from Li_x M. Moreover, the most recent advances in engineering strategies for developing highly active materials and the design of the reaction systems for NH₃ synthesis are covered.

Two-dimensional transition metal borides as high activity and selectivity catalysts for ammonia synthesis

In comparison to defect/doping induced activity in materials, transition metal borides with exposed metal atoms, large specific surface area, and high active site density show advantages as durable and efficient catalysts for specific electrochemical reactions. In this work, ReB₂ for N₂ reduction reaction (NRR) for ammonia (NH₃) with a record-low limiting potential of U_L = -0.05 V and high Faraday efficiency (FE) of 100% is screened out from a new class of TMB₂. It is concluded that high pressure/temperature is favorable to N₂ adsorption and kinetic barrier minimization; the maximal turnover frequency (TOF) at 700 K and 100 bar is 1.24 × 10^-2 per s per site, which is comparable to that of the benchmark Fe₃/Al₂O₃ catalysts, achieving an extremely fast reaction rate. In addition, crystal orbital Hamilton population (COHP) of *N₂ reveals the intrinsic origin of N₂ activation by analyzing the d-2π* interactions, and integrated COHP could be a quantitative descriptor to describe the N₂ activation degree. It is evident that our results not only identify an efficient NRR electrocatalyst in particular, paving the way for sustainable NH₃ production, but also explain the chemical and physical origin of the activity, advancing the design principle for catalysts for various reactions in general.

Dual-site electrocatalytic nitrate reduction to ammonia on oxygen vacancy-enriched and Pd-decorated MnO2 nanosheets

Electrocatalytic nitrate reduction (NRR) represents one promising alternative to the Haber-Bosch process for NH₃ production due to the lower reaction energy barrier compared to N₂ reduction and the potential recycling of nitrogen source from nitrate wastewater. The metal oxides with oxygen vacancy (O_v) display high NH₃ selectivities in NRR (NO₂^-/N₂ as side products), but the complexity in O_v enrichment and the inferior hydrogen adsorption on oxides make NRR an inefficient process. Herein, one superior dual-site NRR electrocatalyst that is composed of O_v-enriched MnO₂ nanosheets (MnO₂-O_v) and Pd nanoparticles (deposited on MnO₂) is constructed over the three-dimensional porous nickel foam (Pd-MnO₂-O_v/Ni foam). In a continuous-flow reaction cell, this electrode delivers a NO₃^--N conversion rate of 642 mg N m^-2_electrode h^-1 and a NH₃ selectivity of 87.64% at -0.85 V vs. Ag/AgCl when feeding 22.5 mg L^-1 of NO₃^--N (0.875 mL min^-1), outperforming the Pd/Ni foam (369 mg N m^-2_electrode h^-1, 85.02%) and MnO₂-O_v/Ni foam (118 mg N m^-2_electrode h^-1, 32.25%). Increasing the feeding NO₃^--N concentration and flow rate to 180.0 mg L^-1 and 2.81 mL min^-1 can further lift the conversion rate to 1933 and 1171 mg N m^-2_electrode h^-1, respectively. The combination of experimental characterizations and theoretical calculations reveal that the MnO₂-O_v adsorbs, immobilizes, and activates the NO₃^- and N-intermediates, while the Pd supplies the O_v sites with sufficient adsorbed hydrogen (H*) for both the NRR and O_v refreshment. Our work presents a good example of utilizing dual-site catalysis in the highly selective conversion of NO₃^- to NH₃ that is important for nitrate pollution abatement, nitrogen resource recycling, as well as sustainable NH₃ production.

Ultra-low-loaded Ni-Fe Dimer Anchored to Nitrogen/Oxygen Sites for Boosting Electroreduction of Carbon Dioxide

Single-atom catalysts (SACs), as a novel emerging category in heterogeneous catalysis, have exhibited superb activity and selectivity within the scope of many catalytic reactions, originating from their nature of atomic dispersion. However, they are not appropriate for more complicated reactions that benefit from multi-metal promotion, such as the carbon dioxide reduction reaction (CO₂ RR). Atomic pair catalysts can provide a synergistic effect to break the intrinsic activity limit. Herein, inspired by theoretical prediction, a hetero-paired atomic-site catalyst (Ni/Fe-N/O-C) was developed for CO₂ RR. Typically, the trace-amount-loaded double-atom-site catalysts exhibited outstanding turnover frequencies (≈460 s^-1 ) surpassing reported ones by far. Interestingly, the loaded metal contents of the three M-N/O-C samples were extremely low, and Ni/Fe-N/O-C exhibited greatly improved durability compared with pure Ni-N/O-C or Fe-N/O-C and excellent CO selectivity above 80 % within a broad potential window of -1.4 to -1.7 V (vs. saturated calomel electrode, 99.8 % at -1.5 V). The superb performance of diatomic-site catalysts was attributed to the adjusted local environment and electron structure of the active center, which could decrease the reaction barrier of *COOH formation. This work presents new insights into manipulating electrocatalytic performance for the development of more sophisticated active sites.

Synergistic Effect of Active Sites of Double-Atom Catalysts for Nitrogen Reduction Reaction

Nitrogen fixation to produce ammonia is a vital process since nitrogen is an essential element for the human body. Industrial nitrogen fixation mainly relies on the Haber-Bosch process. However, this process requires huge energy consumption and leads to pollution emission. In this study, the behaviors of intermediates in the nitrogen reduction reaction (NRR) are investigated for fifteen double-atom catalysts (DACs) through density functional theory calculations, revealing that under the synergistic effect of active sites on appropriate DACs, intermediates can be adsorbed through different configurations according to the activity improvement needs. VFe-N-C shows the best catalytic activity for electrochemical NRR with a limiting potential of -0.36 V vs. the reversible hydrogen electrode. The proposed synergistic effect of active sites on DACs for NRR could provide a new method for design of NRR catalysts.

Novel Design Strategy of High Activity Electrocatalysts toward Nitrogen Reduction Reaction via Boron-Transition-Metal Hybrid Double-Atom Catalysts

Electrocatalytic nitrogen reduction reaction (NRR) is a promising method for sustainable production of NH₃, which provides an alternative to the traditional Haber-Bosch process. However, the poor Faraday efficiency caused by N≡N triple bond activation and competitive hydrogen evolution reaction (HER) have seriously hindered the application of NRR. In this work, a novel strategy to promote NRR through boron-transition-metal (TM) hybrid double-atom catalysts (HDACs) has been proposed. The excellent catalytic activity of HDACs is attributed to a significant difference of valence electron distribution between boron and TMs, which could better activate N≡N bonds and promote the conversion of NH₂ to NH₃ compared with boron or metal single-atom catalysts and traditional double-atom catalysts (DACs). Hence, by means of DFT computations, the stability, activity, and selectivity of 29 HDACs are systematically investigated to evaluate their catalytic performance. B-Ti@g-CN and B-Ta@g-CN are screened as excellent nitrogen-fixing catalysts with particularly low limiting potentials of 0.13 and 0.11 V for NRR and rather high potentials of 0.54 and 0.82 V for HER, respectively. This work provides a new idea for the rational design of efficient nitrogen-fixing catalysts and could also be widely used in other catalytic reactions.

Nanoporous NiSb to Enhance Nitrogen Electroreduction via Tailoring Competitive Adsorption Sites

Ambient nitrogen reduction reaction (NRR) is attracting extensive interest but still suffers from sluggish kinetics owing to competitive rapid hydrogen evolution and difficult nitrogen activation. Herein, nanoporous NiSb alloy is reported as an efficient electrocatalyst for N₂ fixation, achieving a high ammonia yield rate of 56.9 µg h^-1 mg^-1 with a Faradaic efficiency of 48.0%. Density functional theory calculations reveal that in NiSb alloy, Ni favors N₂ hydrogenation while the neighboring Sb separates active sites for proton and N₂ adsorption, which optimizes the adsorption/desorption of intermediates and enables an energetically favorable NRR pathway. This work indicates promising electrocatalytic application of the alloys of 3d and p block metals toward the NRR and provides an intriguing strategy to enhance the reduction of inert molecules by restraining the competitive hydrogen adsorption.

Transition-metal-free boron doped SbN monolayer for N2 adsorption and reduction to NH3: A first-principles study

Electrochemical nitrogen reduction reaction (NRR) in ambient condition is an efficient and sustainable method to synthesize NH₃. In this work, first-principles study was used to discuss the NRR process on B atom doped SbN monolayer. The adsorption of N₂ on B-Sb₁₇N₁₈ and B-S₁₈N₁₇ was calculated including the adsorption energy, adsorption distance, and the charge density difference (CDD). Five different reaction pathways of NRR were taken into consideration and the stability of B-SbN was investigated. The results show that, because the energy of unoccupied orbital in sp³ hybridization of B atom is much lower than that in 2p_z orbitals, the adsorption of N₂ on B-Sb₁₈N₁₇ shows much larger adsorption energy (-1.01 eV with end-on pattern) compared to that of the adsorption on B-Sb₁₇N₁₈. For five different pathways, the 1, 2, and 4 pathways have a smaller limiting potential of about 0.52 V and the limiting step is: *N₂ + H⁺ + e^- → *NNH. The 3 and 5 pathways have a larger limiting potential of 0.57 V with hydrogenation step: *NHNH₂ + H⁺ + e^- → *NH₂NH₂. The B-Sb₁₈N₁₇ is structurally and thermally stable even at 500 K. Our theoretical prediction indicates that B atom substitutionally doped SbN monolayer can be a kind of high-performance metal-free NRR catalyst for NH₃ synthetization, and the work provides attempts for designing and exploring 2D metal-free NRR catalysts.

Anchoring an Fe Dimer on Nitrogen-Doped Graphene toward Highly Efficient Electrocatalytic Ammonia Synthesis

Electrochemical reduction of N₂ to NH₃ based on sustainable energy is a green technique to produce decentralized and on-demand ammonia. In this work, taking graphene as a design platform, we explore the dual-atom catalysts (DACs) via embedding two homonuclear transition metal (TM) atoms into graphene decorated with four neighboring pyrrolic nitrogen atoms (TM₂N₄@graphene) to computationally screen the qualified nitrogen reduction reaction (NRR) catalysts. On the basis of the activity, selectivity, and stability of 15 homonuclear DACs of TM₂N₄@graphene, Fe₂N₄@graphene is identified as the most efficient NRR catalyst with a limiting potential of only -0.32 V. Electronic structure analysis demonstrates that the low oxidation state of Fe (+1) remarkably activates the molecular N₂, which contributes to its excellent NRR catalytic activity. Moreover, the kinetic studies reveal all of the NRR elementary steps exhibiting barriers smaller than that of the hydrogen evolution reaction (HER), showing that HER is effectively suppressed. In addition, we find that the integral crystal orbital Hamilton population (ICOHP) can be used as a descriptor to describe the Gibbs free energy of each step for its NRR performance. This work not only provides theoretical guidance for designing DACs for NRR but also promotes the understanding of DACs for N₂ fixation.

Designing an alkali-metal-like superatom Ca3B for ambient nitrogen reduction to ammonia

Converting earth-abundant nitrogen (N₂) gas into ammonia (NH₃) under mild conditions is one of the most important issues and a long-standing challenge in chemistry. Herein, a new superatom Ca₃B was theoretically designed and characterized to reveal its catalytic performance in converting N₂ into NH₃ by means of density functional theory (DFT) computations. The alkali-metal-like identity of this cluster is verified by its lower vertical ionization energy (VIE, 4.29 eV) than that of potassium (4.34 eV), while its high stability was guaranteed by the large HOMO-LUMO gap and binding energy per atom (E_b). More importantly, this well-designed superatom possesses unique geometric and electronic features, which can fully activate N₂via a "double-electron transfer" mechanism, and then convert the activated N₂ into NH₃ through a distal reaction pathway with a small energy barrier of 0.71 eV. It is optimistically hoped that this work could intrigue more endeavors to design specific superatoms as excellent catalysts for the chemical adsorption and reduction of N₂ to NH₃.

A Feasible Strategy for Identifying Single-Atom Catalysts Toward Electrochemical NO-to-NH3 Conversion

Combining NO removal and NH₃ synthesis, electrochemical NO reduction reaction (NORR) toward NH₃ is considered as a novel and attractive approach. However, exploring suitable catalysts for NO-to-NH₃ conversion is still a formidable task due to the lack of a feasible method. Herein, utilizing systematic first-principles calculations, a rational strategy for screening efficient single-atom catalysts (SACs) for NO-to-NH₃ conversion is reported. This strategy runs the gamut of stability, NO adsorbability, NORR activity, and NH₃ selectivity. Taking transition metal atom embedded in C₂ N (TM-C₂ N) as an example, its validity is demonstrated and Zr-C₂ N is selected as a stable NO-adsorbable NORR catalyst with high NH₃ selectivity. Therefore, this work has established a theoretical landscape for screening SACs toward NO-to-NH₃ conversion, which will contribute to the application of SACs for NORR and other electrochemical reactions.

Controllable CO2 electrocatalytic reduction via ferroelectric switching on single atom anchored In2Se3 monolayer

Efficient and selective CO₂ electroreduction into chemical fuels promises to alleviate environmental pollution and energy crisis, but it relies on catalysts with controllable product selectivity and reaction path. Here, by means of first-principles calculations, we identify six ferroelectric catalysts comprising transition-metal atoms anchored on In₂Se₃ monolayer, whose catalytic performance can be controlled by ferroelectric switching based on adjusted d-band center and occupation of supported metal atoms. The polarization dependent activation allows effective control of the limiting potential of CO₂ reduction on TM@In₂Se₃ (TM = Ni, Pd, Rh, Nb, and Re) as well as the reaction paths and final products on Nb@In₂Se₃ and Re@In₂Se₃. Interestingly, the ferroelectric switching can even reactivate the stuck catalytic CO₂ reduction on Zr@In₂Se₃. The fairly low limiting potential and the unique ferroelectric controllable CO₂ catalytic performance on atomically dispersed transition-metals on In₂Se₃ clearly distinguish them from traditional single atom catalysts, and open an avenue toward improving catalytic activity and selectivity for efficient and controllable electrochemical CO₂ reduction reaction.

High-throughput screening of single metal atom anchored on N-doped boron phosphide for N2 reduction

Developing eco-friendly and highly-efficient catalysts for the electrochemical nitrogen reduction reaction (NRR) under ambient conditions to replace the energy-intensive and environment-polluting Haber-Bosch process is of great significance, while remaining a long-standing challenge in the field of energy conversion today. Herein, through the first principles high-throughput screening, we systematically investigated the catalytic activity of a series of single metal atom immobilized on N-doped boron phosphide (N₃-BP) for N₂ reduction, denoted as MN₃-BP. In particular, a "four-step" screening strategy, involving the structural stability, N₂ chemisorption, low energy cost, as well as good selectivity, was adopted for the stringent screening of the promising MN₃-BP candidates for NRR. Our results unveil that among these candidates, MoN₃-BP eventually stands out, benefiting from its high selectivity and activity, as well as accompanying a considerably favorable limiting potential of -0.25 V for NRR. More impressively, the NRR activity origin of various candidates was revealed by the descriptor φ and ICOHP. Overall, our work not only accelerates the discovery of SACs for converting N₂ into sustainable NH₃ but also provides an exciting impetus for the rational design of NRR catalysts with high stability, high activity, and high selectivity.

Advances in Electrochemical Ammonia Synthesis Beyond the Use of Nitrogen Gas as a Source

Electrocatalytic reduction of dinitrogen has emerged as a new strategy for ammonia synthesis. Despite being environmentally benign and energy-saving, it suffers from low conversion efficiency and short yield of ammonia because of the challenges of activating the inert N≡N bond at room temperature and atmospheric pressure. As a result of this, researchers proposed to reduce the nitrogenous species, one category of air and water pollutants, into valuable ammonia. Although remaining largely underexplored, this alternative approach shows promising efficiency for ammonia synthesis, while achieving high catalytic activity and selectivity remains challenging. In this Minireview, we summarize recent electrocatalytic performances of denitrification with selective formation to ammonia in terms of proposed active sites and reaction mechanisms. Additionally, we discuss the common issues in the state-of-the-art experimental tests and highlight the breakthroughs via computational screening of electrode materials. The aim of this is to steer the future research directions in the field, which is aiming for an optimal catalytic system with higher activity and selectivity for electrocatalytic denitrification.

Mechanistic Insights into the Electrochemical Reduction of CO2 and N2 on the Regulation of a Boron Nitride Defect-Derived Two-Dimensional Catalyst using Density Functional Theory Calculations

Electrochemical reductions of CO₂ (ECRR) and N₂ (ENRR) can not only reduce CO₂ emissions in the air but also make use of N₂ and H₂O, the most extensive resources on earth, to produce high value-added chemicals, which has become one of the hot research directions. In this study, the formation energy (E_f) and dissolution potential (U_diss) of 96 two-dimensional catalysts derived from different defect sites of monoclinic crystal boron nitride (BN) were calculated, and the catalysts with thermodynamic and electrochemical stability were selected. The suitable catalysts for producing HCOOH (Ga/In@N-BN), CO (Sn@BN), and CH₃OH (Co@N-BN) by ECRR and NH₃ (Fe@BN) by ENRR were predicated based on a selective calculation method. The results obtained can provide guidance for the design and development of new catalysts for ECRR and ENRR.

Designing Undercoordinated Ni-Nx and Fe-Nx on Holey Graphene for Electrochemical CO2 Conversion to Syngas

In this study, we propose a top-down approach for the controlled preparation of undercoordinated Ni-N_x (Ni-hG) and Fe-N_x (Fe-hG) catalysts within a holey graphene framework, for the electrochemical CO₂ reduction reaction (CO₂RR) to synthesis gas (syngas). Through the heat treatment of commercial-grade nitrogen-doped graphene, we prepared a defective holey graphene, which was then used as a platform to incorporate undercoordinated single atoms via carbon defect restoration, confirmed by a range of characterization techniques. We reveal that these Ni-hG and Fe-hG catalysts can be combined in any proportion to produce a desired syngas ratio (1-10) across a wide potential range (-0.6 to -1.1 V vs RHE), required commercially for the Fischer-Tropsch (F-T) synthesis of liquid fuels and chemicals. These findings are in agreement with our density functional theory calculations, which reveal that CO selectivity increases with a reduction in N coordination with Ni, while unsaturated Fe-N_x sites favor the hydrogen evolution reaction (HER). The potential of these catalysts for scale up is further demonstrated by the unchanged selectivity at elevated temperature and stability in a high-throughput gas diffusion electrolyzer, displaying a high-mass-normalized activity of 275 mA mg^-1 at a cell voltage of 2.5 V. Our results provide valuable insights into the implementation of a simple top-down approach for fabricating active undercoordinated single atom catalysts for decarbonized syngas generation.

Termination effects of single-atom decorated v-Mo2CTx MXene for the electrochemical nitrogen reduction reaction

The lack of the green, economical and high-efficient catalysts restrict the development of electrochemical nitrogen reduction reaction (NRR). By means of density functional theory (DFT) calculations, we have systematically investigated the NRR catalytic performance of single atoms decorated v-Mo₂CT₂ (T = O, F, OH, Cl, and Li) MXene (TM@v-Mo₂CT₂). Our calculation results reveal the introduction of single atom can significantly improve the NRR activity and selectivity on v-Mo₂CO₂, and Ir@v-Mo₂CO₂ system possesses the lowest limiting potential of only -0.33 V among all studied systems. The termination effects of TM@v-Mo₂CT₂ are further discussed and a descriptor of the adsorption energy of *NNH species (ΔE(*NNH)) is proposed to establish the relationship with NRR limiting potential (U_L(NRR)), in which a moderate (ΔE(*NNH)) is required for high NRR activity. Moreover, a good linear relationship between the ΔE(*NNH) and the excess electrons on Ir atom shows that different ΔE(*NNH) originates from the difference of valence state of Ir atom, which is due to the change of coordination environment. Importantly, the synergistic effects of Ir atom and the surface O-terminations during the first hydrogenation step lead to a promoted NRR performance. Our study might provide new possibilities for rational design of cost-effective MXene-based NRR electrocatalysts.