Tuning the catalytic activity of a single Mo atom supported on graphene for nitrogen reduction via Se atom doping

Atomic Molybdenum Nanomaterials for Electrocatalysis

As a sustainable energy technology, electrocatalytic energy conversion requires electrocatalysts, which greatly motivates the exploitation of high-performance electrocatalysts based on nonprecious metals. Molybdenum-based nanomaterials have demonstrated promise as electrocatalysts because of their unique physiochemical and electronic properties. Among them, atomic Mo catalysts, also called Mo-based single-atom catalysts (Mo-SACs), have the most accessible active sites and tunable microenvironments and are thrivingly explored in various electrochemical conversion reactions. A timely review of such rapidly developing topics is necessary to provide guidance for further exploration of optimized Mo-SACs toward electrochemical energy technologies. In this review, recent advances in the synthetic strategies for Mo-SACs are highlighted, focusing on the microenvironment engineering of Mo atoms. Then, the representative achievements of their applications in various electrocatalytic reactions involving the N2, H2O, and CO2 cycles are summarized by combining experimental and computational results. Finally, prospects for the future development of Mo-SACs in electrocatalysis are provided and the key challenges that require further investigation and optimization are highlighted.

Transition-metal-based Catalysts for Electrochemical Synthesis of Ammonia by Nitrogen Reduction Reaction: Advancing the Green Ammonia Economy

Ammonia (NH3), a cornerstone in the chemical industry, has historically been pivotal for producing various valuable products, notably fertilizers. Its significance is further underscored in the modern energy landscape, where NH3 is seen as a promising medium for hydrogen storage and transportation. However, the conventional Haber-Bosch process, which accounts for approximately 170 million ton of NH3 produced globally each year, is energy-intensive and environmentally damaging. The electrochemical nitrogen reduction reaction (NRR) emerges as a sustainable alternative that operates in ambient conditions and uses renewable energy sources. Despite its potential, the NRR faces challenges, including the inherent stability of nitrogen and its competition with the hydrogen evolution reaction. Transition metals, especially ruthenium (Ru) and molybdenum (Mo), have demonstrated promise as catalysts, enhancing the efficiency of the NRR. Ru excels in catalytic activity, while Mo offers robustness. Strategies like heteroatom doping are being pursued to mitigate NRR challenges, especially the competing hydrogen evolution reaction. This review delves into the advancements of Ru and Mo-based catalysts for electrochemical ammonia synthesis, elucidating the NRR mechanisms, and championing the transition towards a greener ammonia economy. It also seeks to elucidate the core principles underpinning the NRR mechanism. This shift aims not only to address challenges inherent to traditional production methods but also to align with the overarching goals of global sustainability.

Iron Monomers or Trimers on Nitrogen-Doped Carbon: Which Is Better for the Electrocatalytic Nitrogen Reduction Reaction?

The electrocatalytic nitrogen reduction reaction (NRR) presents an alternative method for the Haber-Bosch process, and single-atom catalysts (SACs) to achieve efficient NRR have attracted considerable attention in the past decades. However, whether SACs are more suitable for NRR compared to atomic-cluster catalysts (ACCs) remains to be studied. Herein, we have successfully synthesized both the Fe monomers (Fe1) and trimers (Fe3) on nitrogen-doped carbon catalysts. Both the experiments and DFT calculations indicate that compared to the end-on adsorption of N2 on Fe1 catalysts, N2 activation is enhanced via the side-on adsorption on Fe3 catalysts, and the reaction follows the enzymatic pathway with a reduced free energy barrier for NRR. As a result, the Fe3 catalysts achieved better NRR performance (NH3 yield rate of 27.89 μg h-1 mg-1cat. and Faradaic efficiency of 45.13%) than Fe1 catalysts (10.98 μg h-1 mg-1cat. and 20.98%). Therefore, our research presents guidance to prepare more efficient NRR catalysts.

Synergistic effect of diatomic Mo-B site confined in graphene-like C2N enables electrocatalytic nitrogen reduction via novel mechanism

Structural modulation of the active site with atomic-level precision is of great importance to meet the activity and selectivity challenges that electrocatalysts are commonly facing. In this work, we have designed a metal (M)-nonmetal diatomic site embedded in graphene-like C₂N (denoted as Mo-B@C₂N), where the electrocatalytic N₂ reduction reaction (eNRR) was thoroughly explored using density functional theory combined with the computational hydrogen electrode method. Compared to M-M diatomic sites, the Mo-B site can generate a pronounced synergistic effect that led to eNRR proceeding via a novel quasi-dissociative reaction mechanism that has not been reported relative to the conventional enzymatic, consecutive, distal, and alternating associative mechanism. This newly uncovered mechanism in which N-N bond scission takes place immediately after the first proton-coupled electron transfer (PCET) step (i.e., *NH-*N + H⁺ + e^- → *NH₂*N) has demonstrated much advantage in the PCET process over the four conventional mechanism in terms of thermodynamic barrier, except that the adsorption of side-on *N₂ seemed thermodynamically unfavorable (ΔG_ads = 0.61 eV). Our results have revealed that the activation of the inert N≡N triple bond is dominated by the π*-backdonation mechanism as a consequence of charge transfers from both the B and Mo sites and, unexpectedly, from the substrate C₂N itself as well. Moreover, the hybrid Mo-B diatomic site demonstrated superior performance over either the Mo-Mo or B-B site for driving eNRR. Our study could provide insight into the delicate relationships among atomic site, substrate, and electrocatalytic performance.

Supramolecular confinement pyrolysis to carbon-supported Mo nanostructures spanning four scales for hydroquinone determination

Metal nanostructures with high atom utilization, abundant active sites, and special electron structures should be beneficial to the electrochemical monitoring of hydroquinone (HQ), a highly toxic environmental pollutant. However, traditional nanostructures, especially non-noble metals generally suffer from severe aggregation, or consist of a mixture of nanoparticles and nanoclusters, resulting in low detection sensitivity. Herein, we precisely control the size of Mo-based nanostructures spanning four scales (viz. Mo₂C nanoparticles, Mo₂C nanodots, Mo nanoclusters and Mo single atoms) anchored on N, P, O co-doped carbon support. The detection sensitivity of four samples toward the HQ follows the orders of Mo single atoms＞Mo₂C nanodots＞Mo nanoclusters＞Mo₂C nanoparticles. The catalytic ability of four catalysts is investigated, also showing the same order. The supported Mo single atoms show superior electro-sensing performance for HQ with wide linear range (0.02-200 μM) and low detection limit (0.005 μM), surpassing most previously reported catalysts. Moreover, the coexistence of dihydroxybenzene isomers of catechol (CC) and resorcinol (RC) does not interfere with the detection of HQ on the Mo single-atom sensor. This work opens up a polyoxometalate-based confinement pyrolysis approach to constructing ultrafine metal-based nanostructures spanning multiple-scales for efficient electrochemical applications.

Rational Design of Atomic Site Catalysts for Electrocatalytic Nitrogen Reduction Reaction: One Step Closer to Optimum Activity and Selectivity

The electrocatalytic nitrogen reduction reaction (NRR) has been one of the most intriguing catalytic reactions in recent years, providing an energy-saving and environmentally friendly alternative to the conventional Haber–Bosch process for ammonia production. However, the activity and selectivity issues originating from the activation barrier of the NRR intermediates and the competing hydrogen evolution reaction result in the unsatisfactory NH3 yield rate and Faradaic efficiency of current NRR catalysts. Atomic site catalysts (ASCs), an emerging group of heterogeneous catalysts with a high atomic utilization rate, selectivity, and stability, may provide a solution. This article undertakes an exploration and systematic review of a highly significant research area: the principles of designing ASCs for the NRR. Both the theoretical and experimental progress and state-of-the-art techniques in the rational design of ASCs for the NRR are summarized, and the topic is extended to double-atom catalysts and boron-based metal-free ASCs. This review provides guidelines for the rational design of ASCs for the optimum activity and selectivity for the electrocatalytic NRR.

Graphical Abstract

Rational design of atomic site catalysts (ASCs) for nitrogen reduction reaction (NRR) has both scientific and industrial significance. In this review, the recent experimental and theoretical breakthroughs in the design principles of transition metal ASCs for NRR are comprehensively discussed, and the topic is also extended to double-atom catalysts and boron-based metal-free ASCs.

Screening of transition metal single-atom catalysts supported by a WS2 monolayer for electrocatalytic nitrogen reduction reaction: insights from activity trend and descriptor

The electrocatalytic nitrogen reduction reaction (NRR), as an alternative green technology to the Haber-Bosch process, can efficiently synthesize ammonia under ambient conditions and has a reduced carbon footprint. Here we systematically investigate the NRR activity and selectivity of transition metal (TM) single-atom catalyst (SAC) anchored WS₂ monolayers (TM@WS₂) by means of first-principles calculations and microkinetic modeling. The construction of the reaction activity trend and the identification of an activity descriptor, namely *N₂H adsorption energy, facilitate the efficient screening and rational design of SACs with high activity. Manipulating the adsorption strength of the pivotal *N₂H intermediate is a potential strategy for enhancing NRR activity. Utilizing the limiting potential difference of NRR and the hydrogen evolution reaction (HER) as a selectivity descriptor, we screen three SACs with excellent activity and selectivity toward NRR, i.e., Re@WS₂, Os@WS₂ and Ir@WS₂ with favorable limiting potentials of -0.44 V, -0.38 V and -0.69 V. By using the explicit H₉O₄⁺ model, the kinetic barriers of the rate-determining steps (0.47 eV-1.15 eV) of the solvated proton transfer on the screened SACs are found to be moderate, indicative of a kinetically feasible process. Microkinetic modeling shows that the turnover frequencies of N₂ reduction to NH₃ on Re@WS₂, Os@WS₂ and Ir@WS₂ are 1.52 × 10⁵, 8.21 × 10² and 4.17 × 10^-4 per s per site at 400 K, achieving fast reaction rates. The coexistence of empty and occupied 5d orbitals of candidate SACs is beneficial for σ donation and π* backdonation, endowing them with extraordinary N₂ adsorption and activation. Moreover, the screened SACs possess good dispersity and thermodynamic stability. Our work provides a promising solution for the efficient screening and rational design of high-performance electrocatalysts toward the NRR.

Progress in Mo/W-based electrocatalysts for nitrogen reduction to ammonia under ambient conditions

Ammonia (NH₃), possessing high hydrogen content and energy density, has been widely employed for fertilizers and value-added chemicals in green energy carriers and fuels. However, the current NH₃ synthesis largely depends on the traditional Haber-Bosch process, which needs tremendous energy consumption and generates greenhouse gas, resulting in severe energy and environmental issues. The electrochemical strategy of converting N₂ to NH₃ under mild conditions is a potentially promising route to realize an environmentally friendly concept. Among various catalysts, molybdenum/tungsten-based electrocatalysts have been widely used in electrochemical catalytic and energy conversion. This review describes the latest progress of molybdenum/tungsten-based electrocatalysts for the electrochemical nitrogen reduction reaction. The fundamental roles of morphology, doping, defects, heterojunction, and coupling regulation in improving electrocatalytic performance are mainly discussed. Besides, some tailoring strategies for enhancing the conversion efficiency of N₂ to NH₃ over Mo/W-based electrocatalysts are also summarized. Finally, the existing challenges and limitations of N₂ fixation are proposed, as well as possible future perspectives, which will provide a platform for further development of advanced Mo/W-based N₂ reduction systems.

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.

Theoretical Insights on Au-based Bimetallic Alloy Electrocatalysts for Nitrogen Reduction Reaction with High Selectivity and Activity

Electrochemical reduction of nitrogen to produce ammonia at moderate conditions in aqueous solutions holds great prospect but also faces huge challenges. Considering the high selectivity of Au-based materials to inhibit competitive hydrogen evolution reaction (HER) and high activity of transition metals such as Fe and Mo toward the nitrogen reduction reaction (NRR), it was proposed that Au-based alloy materials could act as efficient catalysts for N₂ fixation based on density functional theory simulations. Only on Mo₃ Au(111) surface the adsorption of N₂ is stronger than H atom. Thermodynamics combined with kinetics studies were performed to investigate the influence of composition and ratio of Au-based alloys on NRR and HER. The binding energy and reorganization energy affected performance for the initial N₂ activation and hydrogenation process. By considering the free-energy diagram, the computed potential-determining step was either the first or the fifth hydrogenation step on metal catalysts. The optimum catalytic activity could be achieved by adjusting atomic proportion in alloys to make all intermediate species exhibit moderate adsorption. Free-energy diagrams of N₂ hydrogenation via Langmuir-Hinshelwood mechanism and hydrogen evolution via Tafel mechanism were compared to reveal that the Mo₃ Au surface showed satisfactory catalytic performance by simultaneously promoting NRR and suppressing HER. Theoretical simulations demonstrated that Au-Mo alloy materials could be applied as high-performance electrocatalysts for NRR.

Shedding Light on the Role of Chemical Bond in Catalysis of Nitrogen Fixation

Ammonia (NH₃ ) and nitrates are essential for human society because of their widespread utilization for producing medicines, fibers, fertilizers, etc. In recent years, the development on nitrogen fixation under mild reaction conditions has attracted much attention. However, the very low conversion efficiency and ambiguous catalytic mechanism remain the major hurdles for the research of nitrogen fixation. This review aims to clarify the role of chemical bond in catalytic nitrogen fixation by summarizing and analyzing the recent development of nitrogen fixation research. In detail, the atomic-scale mechanism of nitrogen fixation reaction, the various methods to improve the nitrogen fixation performance, and the computational investigation of nitrogen fixation are discussed, all from a chemical bond perspective. It is hoped that this review could trigger more profound pondering and deeper exploration in the field of catalytic nitrogen fixation.

Nanomaterials for the electrochemical nitrogen reduction reaction under ambient conditions

As an important chemical product and carbon-free energy carrier, ammonia has a wide range of daily applications in several related fields. Although the industrial synthesis method using the Haber-Bosch process could meet production demands, its huge energy consumption and gas emission limit its long-time development. Therefore, the clean and sustainable electrocatalytic N2 reduction reaction (NRR) operating under conditions have attracted great attention in recent years. However, the chemical inertness of N2 molecules makes it difficult for this reaction to proceed. Therefore, rationally designed catalysts need to be introduced to activate N2 molecules. Here, we summarize the recent progress in low-dimensional nanocatalyst development, including the relationship between the structure and NRR performance from both the theoretical and experimental perspectives. Some insights into the development of NRR electrocatalysts from electronic control aspects are provided. In addition, the theoretical mechanisms, reaction pathways and credibility studies of the NRR are discussed. Some challenges and future prospects of the NRR are also pointed out.

Double boron atom-doped graphdiynes as efficient metal-free electrocatalysts for nitrogen reduction into ammonia: a first-principles study

The electroreduction of dinitrogen (N₂) is an attractive method for ambient ammonia (NH₃) synthesis. In this work, double boron atom-anchored two-dimensional (2D) graphdiyne (GDY-2B) electrocatalysts have been designed and examined for the N₂ reduction reaction (NRR) by density functional theory computations. Our calculations revealed that double boron atoms can be strongly embedded in a graphdiyne monolayer. In particular, configuration GDY-2B(S₂S₂') with two boron atoms substituting two equivalent sp-carbon atoms of diacetylene linkages exhibits excellent catalytic performance for reducing N₂, with an extremely low overpotential of 0.12 V. The "pull-pull" mechanism imposed by doped double boron atoms is responsible for the magnificent effect of N₂ activation. Besides, the competitive reaction of the hydrogen evolution reaction (HER) is suppressed owing to a large ΔG_H* value of -1.25 eV. Based on these results, our study provides useful guidelines for designing effective double atomic catalysts (DACs) based on nonmetal 2D nanosheets for effective electrochemical reduction reactions.

Rational design of nanocatalysts for ambient ammonia electrosynthesis

Ammonia (NH3) is one of the key commercial chemicals and carbon-free energy carriers. It is mainly made by Haber-Bosch process under high temperature and high pressure, which consumes huge amount of energy and releases large amounts of CO2. Developing sustainable approaches to its production is of great importance. Powered by a renewable electricity source, electrochemical N2 reduction reaction (NRR) and nitrate reduction reaction (NITRR) are potential routes to synthesize NH3 under ambient conditions. This review summarizes major recent advances in the NRR and NITRR, especially for several years. Some fundamentals for NRR and NITRR are first introduced. Afterward, the design strategies of nanocatalysts are discussed, mainly focusing on nano-structure construction/nanoconfinement, doping/defects engineering and single-atom engineering. Finally, the critical challenges remaining in this research area and promising directions for future research are discussed.

Theoretical Study on P-coordinated Metal Atoms Embedded in Arsenene for the Conversion of Nitrogen to Ammonia

The conversion of gaseous N2 to ammonia under mild conditions by artificial methods has become one of the hot topics and challenges in the field of energy research today. Accordingly, based on density function theory calculations, we comprehensively explored the d-block of metal atoms (Ti, V, Cr, Mn, Fe, Co, Ni, Nb, Mo, Ru, Rh, W, and Pt) embedded in arsenene (Ars) for different transition systems of phosphorus (P) coordination as potential electrocatalysts for N2 reduction reaction (NRR). By adopting a "two-step" strategy with stringent NRR catalyst screening criteria, we eventually selected Nb@P3-Ars as a research object for a further in-depth NRR mechanism study. Our results show that Nb@P3-Ars not only maintains the thermodynamic stability at mild temperatures but also dominates the competition with the hydrogen evolution reaction when used as the electrochemical NRR (e-NRR) catalyst. In particular, while the NRR process occurs by the distal mechanism, Nb@P3-Ars has a low overpotential (0.36 V), which facilitates the efficient reduction of N2. Therefore, this work predicts the possibility of Nb@P3-Ars as an e-NRR catalyst for reducing N2 from a theoretical perspective and provides significant insights and theoretical guidance for future experimental research.

A mechanistic first-principles study on N2 reduction reaction catalyzed by Ni4 supported defective graphene

The electrochemical reduction of N₂ is an important industrial process, which offers an alternative route to the Haber-Bosch procedure for NH₃ production. Here, by the method of first-principles calculations, we introduce Ni₄ supported defective graphene (Ni₄-Gr) as an efficient substrate to convert N₂ into NH₃. The enzymatic, alternating and distal mechanisms are investigated for N₂ reduction to explore catalytic activity of Ni₄-Gr surface. By analyzing the free energy diagrams, it is obtained that Ni₄-Gr exhibits high catalytic performance for N₂ reduction via the enzymatic pathway with an overpotential value of 0.50 V at normal temperature.

Ammonia Synthesis Using Single-Atom Catalysts Based on Two-Dimensional Organometallic Metal Phthalocyanine Monolayers under Ambient Conditions

We have identified three novel metal phthalocyanine (MPc, M = Mo, Re, and Tc) single-atom catalyst candidates with excellent predicted performance for the production of ammonia from electrocatalytic nitrogen reduction reaction (NRR) through a combination of high-throughput screening and first-principles calculations on a series of 3d, 4d, and 5d transition metals anchored onto extended Pc monolayer catalysts. Analysis of the energy band structures and projected density of states of N₂-MPc revealed significant orbital hybridization and charge transfer between the adsorbed N₂ and catalyst MPc, which accounts for the high catalytic activity. Among 30 MPc catalysts, MoPc and TcPc monolayers were found to be the most promising new NRR catalysts, as they exhibit excellent stability, low onset potential, and high selectivity. A comprehensive reaction pathway search found that the maximum free energy changes for the MoPc and TcPc monolayers are 0.33 and 0.54 eV, respectively. As a distinctive nature of this work, the hybrid reaction pathway was considered extensively and searched systematically. The onset potential of the hybrid pathway is found to be smaller than or comparable to that of the commonly known pure pathway. Thus, the hybrid path is highly competitive with low onset potential and high activity. The hybrid pathway is expected to have an important impact on future research on the mechanism of NRR, and it will open up a new way to explore the mechanism of the NRR reaction. We hope that our work will provide impetus to the creation of new catalysts for reduction of N₂ to NH₃. This work provides new insights into the rational design of NRR catalysts and explores novel reaction pathways under ambient or mild conditions.

Single atom-doped arsenene as electrocatalyst for reducing nitrogen to ammonia: a DFT study

Due to the wide application of NH3 in the energy and chemical industry, the rational design of a highly efficient and low-cost electrocatalyst for nitrogen fixation at moderate conditions is highly desirable to meet the increasing demand for sustainable energy production in the modern society. Herein, we have systematically studied the catalytic performance of transition metal (TM) atom (i.e., V, Cr, Fe, Co, Cu, Ru, Pd, Ag, Pt, Au)-doped arsenene nanosheet, a new two-dimensional (2D) nanomaterial in VA group, as a heterogeneous catalyst for nitrogen reduction reaction (NRR). By density functional theory (DFT) calculation and systematic theoretical screening, our study predicts that the systems of V-, Fe-, Co- and Ru-doped arsenene have promising potentials as NRR electrocatalysts with high-loading TM and highly stable adsorption of N2 molecule. Particularly, the V-doped system exhibits two feasible configurations for N2 adsorption and an ultralow overpotential (0.10 V) via the enzymatic pathway, which is very competitive among similar reported electrocatalysts. This theoretical study not only extends the electrocatalyst family for nitrogen fixation, but also further deepens our physical insights into catalytic improvement, which can be expected to guide the rational design of novel NRR catalysts.

Exploration and Investigation of Periodic Elements for Electrocatalytic Nitrogen Reduction

High demand for green ecosystems has urged the human community to reconsider and revamp the traditional way of synthesis of several compounds. Ammonia (NH₃ ) is one such compound whose applications have been extended from fertilizers to explosives and is still being synthesized using the high energy inhaling Haber-Bosch process. Carbon free electrocatalytic nitrogen reduction reaction (NRR) is considered as a potential replacement for the Haber-Bosch method. However, it has few limitations such as low N₂ adsorption, selectivity (competitive HER reactions), low yield rate etc. Since it is at the early stage, tremendous efforts have been devoted in understanding the reaction mechanism and screening of the electrocatalysts and electrolytes. In this review, the electrocatalysts are classified based on the periodic table with heat maps of Faraday efficiency and yield rate of NH₃ in NRR and their electrocatalytic properties toward NRR are discussed. Also, the activity of each element is discussed and short tables and concise graphs are provided to enable the researchers to understand recent progress on each element. At the end, a perspective is provided on countering the current challenges in NRR. This review may act as handbook for basic NRR understandings, recent progress in NRR, and the design and development of advanced electrocatalysts and systems.

Nitrogen fixation on a single Mo atom embedded stanene monolayer: a computational study

Designing effective electrocatalysts for N₂ fixation to NH₃ under mild conditions is important and challenging. In this work, we explored the feasibility of transition metal atom embedded stanene as an effective catalyst for the nitrogen reduction reaction (NRR) based on first-principles calculations. The results reveal that Mo atom embedded stanene possesses high stability and good electrical conductivity. Specifically, Mo atom embedded stanene exhibits excellent catalytic activity for NRR with an over-potential of only 0.50 V along the mixed pathway. This low over-potential is due to the acceptance and back donation of electrons between the transition metal and N₂ molecules. Furthermore, due to the preferential adsorption of N₂ relative to H, competition from the hydrogen evolution reaction (HER) can be inhibited effectively. The fairly low over-potential and high electrical conductivity make Mo-embedded stanene promising for NRR. Our theoretical results indicate that stanene could be a new and effective anchoring material for TM-based catalysts for NRR.

Feasibility of N2 Reduction on the V Anchored 1T-MoS2 Monolayer: A Density Functional Theory Study

Developing efficient electrocatalysts for nitrogen reduction reaction (NRR) at ambient conditions is crucial for NH₃ synthesis. In this manuscript, the NRR performance of the transition metal anchored MoS₂ monolayer with 1T atomic structure (1T-MoS₂ ) is systematically evaluated by density functional theory computations. Our results reveal that the V decorated 1T-MoS₂ exhibits the outstanding catalytic activity toward NRR via distal mechanism where the corresponding onset potential is 0.66 V, being superior to the commercial Ru material. Furthermore, the powerful binding energy between the V atom and the 1T-MoS₂ provides the good resistance against clustering of the V dopant, indicating its stability. Overall, this work provides a potential alternative for the application of NH₃ synthesis.

Graphdiyne coordinated transition metals as single-atom catalysts for nitrogen fixation

The reduction of N₂ molecules to NH₃ is a very challenging task in chemistry. The electrocatalytic nitrogen reduction reaction (NRR) is a promising technology for NH₃ synthesis. By using first-principles calculation, a new class of single-atom catalysts (SACs), graphdiyne coordinated single transition metal atoms (TM@GDY, TM = Sc-Zn, Y-Cd, and La-Hg) were designed, and the NRR catalytic character of TM@GDY was systematically investigated. The results demonstrated that some TM@GDY (TM = Ti, V, Fe, Co, Zr, Rh, and Hf) monolayers exhibit better NRR activities than a Ru(0001) stepped surface. There is an obvious linear correlation between the limiting potential and the atomic N adsorption energy, which confirms that the N adsorption energy may be a descriptor for evaluation of the NRR catalytic performance. The V@GDY monolayer possesses the best NRR catalytic character with the lowest limiting potential of -0.67 V and the potential-limiting step (PLS) of *N₂→ *NNH for both alternating and distal mechanisms. Our results highlight a new family of efficient and stable TM@GDY catalysts and provide useful guidelines for SAC development and practical applications.

Theoretical screening of efficient single-atom catalysts for nitrogen fixation based on a defective BN monolayer

The electrocatalytic reduction of naturally abundant N2 to NH3 is an attractive approach to replace the Haber-Bosch nitrogen-fixation process that causes enormous energy consumption and greenhouse gas emissions. However, designing high-performance catalysts toward the electrocatalytic N2 reduction reaction (eNRR) remains one of the greatest challenges in this area. Herein, high-throughput screening of catalysts for the NRR among a series of transition metal atoms supported on a defective hexagonal boron nitride (h-BN) nanosheet is performed through spin-polarized density functional theory (DFT) computations. Strikingly, among the 18 candidates, the V/Tc atom anchored on a defective h-BN monolayer (V@BN and Tc@BN) showed good NRR activity with relatively low onset potentials. Particularly, V@BN was found to exhibit outstanding catalytic activity for the NRR via an enzymatic pathway with an extremely low overpotential of 0.25 V. The value is significantly lower than that on the Ru (0001) stepped surface that has the best NRR catalytic performance among bulk metal catalysts. The novel NRR activity of V@BN is attributed to the enhanced electrical conductivity due to V-doping, the "donation-backdonation" process for N2 activation, and the highly centralized spin-polarization on the V atom. This work not only provides a quite promising catalyst for the NRR but also provides new insights for the rational design of single-atom NRR catalysts.

A thermodynamic and kinetic study of the catalytic performance of Fe, Mo, Rh and Ru for the electrochemical nitrogen reduction reaction

Potential energy curves of Fe(110) and Rh(111) at the corresponding equilibrium electrodes.