N2 Reduction Reaction Research Articles

A Universal Descriptor for Complicated Interfacial Effects on Electrochemical Reduction Reactions.

Supported catalysts have exhibited excellent performance in various reactions. However, the rational design of supported catalysts with high activity and certain selectivity remains a great challenge because of the complicated interfacial effects. Using recently emerged two-dimensional materials supported dual-atom catalysts (DACs@2D) as a prototype, we propose a simple and universal descriptor based on inherent atomic properties (electronegativity, electron type, and number), which can well evaluate the complicated interfacial effects on the electrochemical reduction reactions (i.e., CO2, O2, and N2 reduction reactions). Based on this descriptor, activity and selectivity trends in CO2 reduction reaction are successfully elucidated, in good agreement with available experimental data. Moreover, several potential catalysts with superior activity and selectivity for target products are predicted, such as CuCr/g-C3N4 for CH4 and CuSn/N-BN for HCOOH. More importantly, this descriptor can also be extended to evaluate the activity of DACs@2D for O2 and N2 reduction reactions, with very small errors between the prediction and reported experimental/computational results. This work provides feasible principles for the rational design of advanced electrocatalysts and the construction of universal descriptors based on inherent atomic properties.

Atomically Dispersed Uranium Enables an Unprecedentedly High NH3 Yield Rate

The low NH3 yield rate is a grand challenge for electrocatalytic N2 reduction to NH3. Herein, we report the first uranium single-atom catalyst (SAC) capable of catalyzing the electrochemical N2 reduction reaction (NRR). The uranium SAC features a low limiting potential (<0.5 V) and near-zero free energy changes for N2 adsorption and NH3 desorption. The integration of these merits enables the uranium SAC to afford an unprecedentedly high NH3 yield rate, 3-4 orders of magnitude higher than that of the Ru(0001) surface, which is widely recognized as an excellent NRR electrocatalyst. Further theoretical analysis reveals that the N2 reduction catalyzed by the uranium SAC is synergistically regulated by the d and f electrons of atomic uranium. This work proposes a promising solution (that is, atomically dispersed uranium) to the daunting challenge associated with the low NH3 yield rate, thus enabling the scalable production of NH3 via electrochemical N2 reduction.

Breaking the Scaling Relationship Limit: From Single-Atom to Dual-Atom Catalysts

ConspectusRecent decades have witnessed the rapid development of catalytic science, especially after Taylor and Armstrong proposed the notion of the “active site” in 1925. By optimizing reaction paths and reducing the activation energies of reactions, catalysts appear in more than 90% of chemical production reactions, involving homogeneous catalysis, heterogeneous catalysis, and enzyme catalysis. Because of the 100% efficiency of active atom utilization and the adjustable microenvironment of metal centers, single-atom catalysts (SACs) shine in various catalytic fields for enhancing the rate, conversion, and selectivity of chemical reactions. Nevertheless, a solo active site determines a fixed adsorption mode, and the adsorption energies of intermediates from multistep reactions linking with a solo metal site are related to each other. For a specific multistep reaction, it is almost impossible to optimally adjust the adsorption of every intermediate on the solo site simultaneously. This phenomenon is termed the scaling relationship limit (SRL) and is an unavoidable obstacle in the development of pure SACs.Dual-atom catalysts (DACs), perfectly inheriting the advantages of SACs, can exhibit better catalytic performance than simple SACs and thus have gradually gained researchers’ attention. Depending on the dual-metal structure, dual-metal sites (DMSs) in DACs can be divided into two separated heterometal sites, two linked homometal sites, and two linked heterometal sites. Two separated heterometal sites prescribe a distance limit between two metal sites for electron interaction. Currently, the active origins of DACs can be summarized in the following three points: (1) electronic effect, in which only one metal center serves as active site and the other plays an electronic regulatory role; (2) synergistic effect, in which two metal centers separately catalyze different core steps to improve catalytic performance together; (3) adsorption effect, in which offering additional sites changes the adsorption structures to break the SRL based on SACs. Among the three active origins, optimizing the adsorption structure of intermediates upon DMSs is one of the most effective technologies to boost the catalytic property of DACs on the basis of SACs. To date, few contributions have focused on the development of DACs in various heterogeneous catalysis environments, including O2 reduction reaction, O2 evolution reaction, H2 evolution reaction, CO2 reduction reaction, N2 reduction reaction, and other conversion reactions.In this Account, a summary of recent progress regarding DACs in heterogeneous catalysis will be presented. First, the evolution of DACs from an unpopular discovery to research hot spot is illustrated through a timeline. In the next section, the DACs are divided into three categories, and the potential active origins of DACs are revealed by comparison with SACs. In addition, the techniques for constructing DACs are systematically summarized, including preparation of carbonous, pyrolysis-free, noncarbon-supported, and complex-type DACs. Furthermore, the underlying active origins of DACs in specific energy- and environment-related reactions are introduced in detail with assistance of theoretical calculations. Finally, we affirm the contribution of DACs to catalysis, particularly heterogeneous electrocatalysis, and provide an outlook regarding the development direction for DACs by discussing the major challenges. It is anticipated that this Account can inspire researchers to propel the advance of DACs.

Lithium-Mediated Electrochemical Nitrogen Reduction: Tracking Electrode–Electrolyte Interfaces via Time-Resolved Neutron Reflectometry

We employed time-resolved, in situ neutron reflectometry to observe a dynamic electrode–electrolyte interface under conditions relevant to Li-mediated electrochemical N2 reduction reaction (NRR). This method leverages the sensitivity of neutrons to Li and fast time resolution (∼1 min) to observe the formation of a layer containing Li species at the electrode surface within minutes of applying a current density (−0.1 mA/cm2). Notably, within the first 6 min, we did not observe a solid-electrolyte interphase (SEI) distinct from this layer, providing insight into recent reports demonstrating performance advantages of short current cycles interspersed with open-circuit conditions for NRR. At longer time scales following chronopotentiometry (∼2 h), a multilayer SEI remained, though the presence of Li was not evident, indicating that the layers containing Li species observed over shorter time scales degrade almost entirely under open-circuit conditions, leaving SEI layers consisting of electrolyte decomposition products. We thus present the first application of neutron reflectometry toward the NRR─through fast time-resolved measurements, we have enabled a path toward understanding the electrochemical NRR as well as dynamic systems across a wide range of energy technologies.

Photocatalytic Dinitrogen Fixation with Water on High-Phosphorus-Doped Carbon Nitride with Surface Nitrogen Vacancies.

Sunlight-driven photocatalytic dinitrogen (N2) fixation with water at ambient conditions is of vital importance for a sustainable energy society. The efficiency of this reaction, however, is still low because of the difficulty in promoting both water oxidation and N2 reduction reactions. Herein, we report that a high-phosphorus-doped carbon nitride with surface nitrogen vacancies (PCN(V)) synthesized by thermal condensation under a hydrogen (H2) atmosphere using phosphorus oxide (P2O5) as a phosphorus source efficiently promotes N2 fixation. The large numbers of the doped P atoms on the PCN(V)-P2O5 catalysts enhance the oxidation of water, while the N vacancies reduce N2, facilitating efficient ammonia (NH3) generation with an apparent quantum yield at 420 nm of 3.4%. Simulated sunlight illumination of the catalyst in water under N2 bubbling produces NH3 with a solar-to-chemical conversion efficiency of 0.16%, which is the highest efficiency among the previously reported powder photocatalysts.

Theoretical study of transition metal doped α-borophene nanosheet as promising electrocatalyst for electrochemical reduction of N2

Ammonia synthesis is an essential industrial production process. Through first principle calculations, this work investigated 3d/4d transition metal (TM) embedded α-borophene monolayer (BM-α) as efficient electrocatalyst for N2 reduction reaction (NRR). The computational results show that V, Cr, and Mo@BM-α exhibit excellent catalytic activity for ammonia synthesis via the enzymatic pathway. Analyses reveal that the unoccupied d orbitals of TM (V, C, and Mo) accept lone pair electrons from N2 while the anti-bonding orbitals of N2 accept a large amount of negative charge from TM, which lead to the elongation of the NN triple bond, thus effectively activating the nitrogen. In addition, V@BM-α and Mo@BM-α show a strong suppressive effect on hydrogen evolution reaction (HER) and overcome the possible oxidation on the catalyst surface. Our results demonstrate the α-borophene is a superior substrate for single atom catalysts which can be designed as high performance NRR electrocatalysts.

The mechanism of nitrogen reduction reaction on defective boron nitride (BN) monolayer doped with monatomic Co, Ni, and Mo–A first principles study

In this work, transition metal atoms (TM=Co, Ni, Mo) doped with B defect (M-VB-BN) and N defect (M-VN-BN) boron nitride (BN) monolayer was constructed and used for the synthesis of ammonia with N2 and *H as raw materials (TM=Co, Ni, Mo). Based on the density functional theory (DFT), the structure of these six modified materials was optimized, and the simulation calculation of the N2 reduction reaction (N2RR) was carried out. It shows that the type of defects and TM will affect the reaction path. For Co-VB-BN and Ni-VB-BN, the most potential path is the alternate mechanism; Mo-VN-BN is most inclined to the enzymatic mechanism. In particular, for Co-VN-BN, Ni-VN-BN and Mo-VB-BN, the N2RR does not proceed from beginning to end according to any of the three basic mechanisms. It is manifested as a mixed mechanism in which the enzymatic mechanism and the associative mechanism are interleaved. In general, N defect is more suitable for N2RR than B defect. Among the six structures, Mo-VN-BN exhibits the highest catalytic activity, and its energy barrier for rate-determining step is only 0.24 eV. These findings can provide a certain reference for the selection of defect sites and transition metals in the study of two-dimensional BN material catalysts.

Mechanistic Insights into Electrocatalytic Nitrogen Reduction Reaction on the Pd‐W Heteronuclear Diatom Supported on C2N Monolayer: Role of H Pre‐Adsorption

The electrocatalytic N2 reduction reaction (eNRR) is a potential alternative to the Haber–Bosch process for ammonia (NH3) production. Tremendous efforts have been made in eNRR catalyst research to promote the practical application of eNRR. In this work, by means of density functional theory calculations and the computational hydrogen electrode model, we evaluated the eNRR performance of 30 single metal atoms supported on a C2N monolayer (M@C2N), and we designed a new thermodynamically stable Pd‐W hetero‐metal diatomic catalyst supported on the C2N monolayer (PdW@C2N). We found that PdW@C2N prefers to adsorb H over N2, and then, the pre‐generated hydrogen‐terminated PdW@C2N selectively adsorbing N2 behaves as the actual functioning “catalyst” to catalyze the eNRR process, exhibiting excellent performance with a low overpotential (0.31 V), an ultra‐low NH3 desorption free energy (0.05 eV), and a high selectivity toward eNRR over hydrogen evolution reaction (HER). Moreover, PdW@C2N shows a superior eNRR performance to its monomer (W@C2N) and homonuclear diatom (W2@C2N) counterparts. The revealed mechanism indicates that the preferential H adsorption over N2 on the active site may not always hamper the eNRR process, especially for heteronuclear diatom catalysts. This work encourages deeper exploration on the competition of eNRR and HER on catalyst surfaces.

Rational design of highly efficient electrocatalytic single-atom catalysts for nitrogen reduction on nitrogen-doped graphene and g-C2N supports

Electrochemical N2 reduction reaction (NRR) is a very attractive route for ammonia production under ambient conditions. It is a challenging issue to develop efficient electrocatalysts in NRR process. Herein, we designed a series of NRR single-atom catalysts (SACs), namely, transition metal single-atom anchored on nitrogen-doped porous graphene with six-fold N6 cavity (TM@N6-G). Based on spin-polarized density functional theory (DFT) calculations, the stability and catalytic performance of TM@N6-G SACs were systemically investigated. Six promising catalysts (Nb, Mo, Tc, Ta, W, and Re@N6-G) are selected from 14 candidates by screening the free energy changes of the first and last electric chemical steps. Detailed NRR mechanism studies show that the six SACs have superior electrochemical NRR performance, especially W@N6-G, reaching low limiting potentials of −0.23 V. Furthermore, we extend the present study to another kind of graphitic carbon nitrides, g-C2N, which has a similar N6 cavity. Our calculations show that five TM@g-C2N SACs have good stability and high activity and selectivity for NRR. In addition, ΔG*NNH, dN-N, and ICOHP can be used as descriptors to understand the origin of NRR catalytic activity of these two kinds of catalysts. The present work may provide valuable clues for exploring promising and efficient NRR electrochemical catalysts.

Engineering local environment of ruthenium by defect-tuned SnO2 over carbon cloth for neutral-media N2 electroreduction

Electrocatalytic N2 reduction reaction (NRR) is of great potential as a sustainable and alternative technique to the energy-intensive Haber-Bosch process for NH3 production. However, its practical applications are impeded by the low NH3 yield and Faradaic efficiency (FE) mainly due to the inert N≡N triple bond and the competing hydrogen evolution reaction (HER). Herein, ruthenium-doped defect-rich SnO2 nanoparticles on carbon cloth (Ru–SnO2/CC) are synthesized for efficient electrocatalytic NRR under ambient conditions. The catalysts exhibit an NH3 yield of 4.83 μg h−1 cm−2 with a FE of 17.01% at −0.2 V vs. reversible hydrogen electrode in 0.1 M Na2SO4. The integration of Ru species, SnO2 and oxygen vacancies leads a synergistic catalytic system, in which the semiconducting SnO2 particles not only stabilize the Ru active centers but also suppress the HER, while the oxygen vacancies in SnO2 lattice help to promote the N2 adsorption and enhance the activity of the Ru active centers. Overall, this synergy result in a unique local environment around the Ru active sites that favors the NRR process, which is further reinforced by the binder-free and facile electron transfer nature of CC, leading to the outstanding NRR catalytic activity and durability. These results outperform majority of the noble-metals-based electrocatalysts under similar conditions. This metal-doping tuned local environment manipulation may open up a promising avenue to the design and fabrication of efficient catalysts for N2 electroreduction.

Electrodeposition: An efficient method to fabricate self-supported electrodes for electrochemical energy conversion systems.

The development of electrocatalysts for energy conversion systems is essential for alleviating environmental problems and producing useful energy sources as alternatives to fossil fuels. Improving the catalytic performance and stability of electrocatalysts is a major challenge in the development of energy conversion systems. Moreover, understanding their electrode structure is important for enhancing the energy efficiency. Recently, binder-free self-supported electrodes have been investigated because the seamless contact between the electrocatalyst and substrate minimizes the contact resistance as well as facilitates fast charge transfer at the catalyst/substrate interface and high catalyst utilization. Electrodeposition is an effective and facile method for fabricating self-supported electrodes in aqueous solutions under mild conditions. Facile fabrication without a polymer binder and controlability of the compositional and morphological properties of the electrocatalyst make electrodeposition methods suitable for enhancing the performance of energy conversion systems. Herein, we summarize recent research on self-supported electrodes fabricated by electrodeposition for energy conversion reactions, particularly focusing on cathodic reactions of electrolyzer system such as hydrogen evolution, electrochemical CO2 reduction, and electrochemical N2 reduction reactions. The deposition conditions, morphological and compositional properties, and catalytic performance of the electrocatalyst are reviewed. Finally, the prospective directions of electrocatalyst development for energy conversion systems are discussed.

Regulating MoS2 edge site for photocatalytic nitrogen fixation: A theoretical and experimental study

The creation of active sites on semiconductor catalysts for the adsorption of N2 and dissociation of nonpolar N≡N bond is a key issue for photocatalytic N2 reduction reaction (PNRR). According to density function theory calculation on MoS2, the Mo rather than the S edge sites are active, and those on basal planes not. It is disclosed that Mn doping is an effective way to boost the activity of MoS2 by modifying the edge sites. The Mn-modified MoS2 has higher exposure of Mo edge sites due to the formation of S vacancies. It is noted that the activity of original Mo edge sites remains unaltered, while the inertness of S edge sites for N2 adsorption moderated. Furthermore, the injection of electrons into the N≡N bond is promoted, leading to lowering of energy barrier for N2 reduction. Finally, through a simple hydrothermal method we prepared MoS2 that is rich in edge sides at the basal plane by Mn doping. High ammonia production rate of up to 213.2 μmol g−1h−1 is achieved, which is 5.3 times that of pristine MoS2 and superior to most of the reported MoS2-based photocatalysts in the absence of sacrificial agent.

One-dimensional screw-like MoS2 with oxygen partially replacing sulfur as an electrocatalyst for the N2 reduction reaction

• One-dimensional screw-like MoS 2 with oxygen partially replacing sulfur nanosheets are active for NRR. • 1D-MoS 2-x O y nanosheets achieve a large NH 3 yield of 5.56 × 10 -8 mol s −1 cm −2 at −0.35 V vs. RHE. • 1D-MoS 2-x O y nanosheets attain a relatively high Faradaic efficiency of 9.86% at −0.3 V vs. RHE. • 1D-MoS 2-x O y nanosheets show high electrochemical stability. Electrocatalytic nitrogen reduction reaction (NRR) is considered to be an energy-saving method for the production of NH 3 . However, it is still very challenging to achieve a high NH 3 yield and efficiency under ambient conditions. Herein, we for the first time synthesize one-dimensional screw-like MoS 2 with oxygen partially replacing sulfur (1D-MoS 2-x O y ) nanosheets by a one-step solvothermal method as an efficient non-noble metal electrocatalyst for NRR. In a 0.1 M HCl solution, 1D-MoS 2-x O y exhibits excellent NRR performance, with a remarkable average ammonia yield rate of 5.56 × 10 -8 mol s −1 cm −2 at −0.35 V, and a high Faradaic efficiency of 9.86% at −0.3 V. The isotope labeling experiment proves that the generation of NH 3 is completely derived from the feed-in N 2 . Density functional theory calculations show that MoS 2 with oxygen partially replacing sulfur can reduce the Gibbs free energy of the potential determination step (PDS). Besides, the unique screw-like structure can provide more N 2 adsorption sites for NRR. This work proposes a promising strategy for the reasonable design of non-precious metal-based NRR electrocatalysts.

Density functional theory study of nitrogen-doped black phosphorene doped with monatomic transition metals as high performance electrocatalysts for N2 reduction reaction

Ammonia (NH3) is an essential resource in human production and living activities, and its demand has been rising in recent years. The catalytic synthesis of NH3 from N2 under mild conditions, inspired by biological nitrogen fixation, has piqued the interest of researchers. In this paper, density functional theory (DFT) calculations were used to investigate the catalytic activity, mechanism, and selectivity of the TM embedded nitrogen-doped phosphorene as high-performance nitrogen reduction reaction (NRR) electrocatalysts in depth. The results show that Nb- and Mo-doped catalysts present excellent catalytic performance, with low limiting potentials of −0.41 and −0.18 V, respectively. The Mo–N3–BP catalyst, for example, not only has an extremely low overpotential (−0.02 V), but also presents superior selectivity to effectively inhibit the HER competition reaction. A deeper look into the catalytic mechanism reveals a volcano relationship between the d-band center and the catalytic activity (Mo and Nb are located near the peak of the volcano-type curve). The d-band center and charge of the metal center can be regarded as effective descriptors for NRR activity on TM embedded nitrogen-doped phosphorene electrocatalysts, which hope to serve as a guiding principle for the design of high performance NRR single-atom catalyst in the future.

Atomic Molybdenum for Synthesis of Ammonia with 50% Faradic Efficiency.

The electrochemical dinitrogen (N2 ) reduction reaction (NRR) under ambient conditions has gained significant interest as an environmentally friendly alternative to the traditional Haber-Bosch process for the synthesis of ammonia (NH3 ). However, up to now, most of the reported NRR electrocatalysts with satisfactory catalytic activities have been hindered by the large overpotential in N2 activation. The preparation of highly efficient Mo-based NRR electrocatalyst in acidic electrolytes under ambient conditions is demonstrated here, consisting of stabilized single Mo atoms anchored on holey nitrogen-doped graphene synthesized through a convenient potassium-salt-assisted activation method. At -0.05V versus a reversible hydrogen electrode (RHE), an electrode consisting of the resultant electrocatalyst immobilized on carbon fiber paper can attain an exceptional Faradaic efficiency of 50.2% and a NH3 yield rate of 3.6µg h-1 mgcat-1 with low overpotentials. Density functional theory calculations further unveil that compared to the original graphene without holes, the edge coordinated Mo atoms and the existence of vacancies on holey graphene lower the overpotential of N2 reduction, thereby promoting the NRR catalytic activity. This work could provide new guidelines for future designs in single-atom catalysis that would be beneficial to ambient N2 fixation, and replacement of classical synthesis processes that are very energy-intensive.

MXene Quantum Dots/Copper Nanocomposites for Synergistically Enhanced N2 Electroreduction

Electrocatalytic N2 reduction reaction (NRR) represents an appealing solution for sustainable ammonia production, whereas exploring high‐efficiency NRR catalysts is highly desired but extremely challenging. Herein, we combine Ti3C2Tx‐MXene quantum dots (MQDs) with porous Cu nanosheets to design a novel heterostructured MQDs/Cu as an effective and durable NRR catalyst. Impressively, MQDs/Cu showed a synergistically enhanced NRR activity with an NH3 yield of 78.5 μg h−1 mg−1 (−0.5 V) and a Faradaic efficiency of 21.3% (−0.4 V), far superior to pure MQDs and Cu, and outperforming the majority of the state‐of‐the‐art NRR catalysts. Density function theory computations demonstrated that the synergy of MQDs and Cu enabled the creation of interfacial Cu‐Ti dimer as dual‐active‐centers to strongly activate the absorbed N2 and promote the *N2H formation, consequently resulting in the much reduced energy barriers and greatly enhanced NRR performance.

Vacancy-enhanced Mo-N2 interaction in MoSe2 nanosheets enables efficient electrocatalytic NH3 synthesis

NH3 plays an essential role in human life since it is an important raw material for fertilizers, plastics and rubbers production. As an NH3 synthesis technology under ambient conditions, electrocatalytic N2 reduction reaction (NRR) has great potential to replace the energy-intensive Haber-Bosch process. The key of electrocatalytic NRR is the exploration of efficient catalysts. Transition metal Mo is promising since it exists naturally in nitrogenase due to the unique Mo-N2 interaction; particularly in the form of 2D material such as MoSe2, the surface area is maximized for more active sites. However, the NRR performance of MoSe2 is still unsatisfactory because Mo is only exposed at the semi-open edge, and the electronegative Se-mantled surface area remains inaccessible to N2. Herein, we propose a simple and effective strategy to create high-concentration Se vacancies in MoSe2 through heteroatom doping induced lattice strain, which effectively enhances the Mo-N2 interaction on the surface area. In result, high NH3 yield (3.04 × 10–10 mol s–1 cm–2) and Faraday efficiency (21.61%) are attained at –0.45 V vs. RHE in 0.1 mol/L Na2SO4.

Photoelectrocatalytic nitrogen fixation with Vo-BiOBr/TiO2 heterostructured photoelectrode as photocatalyst

Photocatalytic or photoelectrocatalytic nitrogen fixation is considered as a very promising way to reduce energy requirements. Here, Vo-BiOBr/TiO2 nanocomposite photoelectrode was constructed by modifying TiO2 nanotube arrays with BiOBr nanosheets with oxygen vacancies (Vo) for photoelectrocatalytic nitrogen fixation. The oxygen vacancy promotes the adsorption and activation of N2 on the catalyst surface. The Lewis basicity of nitrogen is enhanced by transferring the photogenerated electrons on the conduction band of BiOBr to the π anti-bonding orbit of N2, which is more beneficial for the addition of protons. On the other hand, the heterojunction between TiO2 and Vo-BiOBr facilitates the separation of photogenerated carriers. The photogenerated holes on the valence band of TiO2 travelled to the counter electrode to produce oxygen at a negative potential, avoiding the further oxidation of NH3. Vo-BiOBr/TiO2 displays a high NH3 production rate of 25.08 μg h−1 cm−2 at −0.2 V which is 3.3 times higher than that of BiOBr/TiO2. The synergistic effect between TiO2 and Vo-BiOBr results in enhanced light absorption and higher photoelectrocatalytic efficiency for the N2 reduction reaction.

Lithium-Assisted Dinitrogen Reduction Mediated by Nb2LiNO1-4- Cluster Anions: Electron Donors or Structural Units.

Alkali atoms are usually used as promoters to significantly increase the catalytic activity of transition-metal catalysts in a wide range of reactions such as dinitrogen conversion reactions. However, the role of alkali metal atoms remains controversial. Herein, a series of quaternary cluster anions containing lithium atoms Nb2LiNO1-4- have been synthesized and reacted with N2 at room temperature. The detailed experimental and theoretical investigations indicate that Nb2LiNO- is capable to cleave the N≡N bond and the Li atoms in Nb2LiNO1,2- act as electron donors in the N2 reduction reaction. With the increase in the number of oxygen atoms, the reactivity toward N2 is reduced from adsorption via a side-on end-on mode in Nb2LiNO2- to the inertness of Nb2LiNO4-. In Nb2LiNO3,4- anions, the Li atoms are bonded with oxygen atoms, acting as structural units to stabilize structures. Therefore, the roles of alkali atoms are able to change with different chemical environments of active sites. For the first time, we reveal how the number of ligands (oxygen atoms herein) can be used to finely regulate the reactivity toward N2.

Interface engineered Sb2O3/W18O49 heterostructure for enhanced visible-light-driven photocatalytic N2 reduction

The direct photochemical N2 reduction reaction boasts the potential for clean and sustainable NH3 manufacturing, yet achieving this remains a significant challenge. To activate and cleave the nonpolar N≡N bond and accelerate the transport and separation of charge carriers during photocatalysis, the design and facile synthesis of active, robust, cheap, and earth-abundant photocatalysts is crucial. Here, we demonstrate efficient and stable visible light fixation of N2 to NH3 by constructing a novel heterostructure consisting of two-dimensional Sb2O3 nanosheets and one-dimensional W18O49 nanowires. A remarkable NH3 production rate of up to 731 μgNH3 h−1 gcat.−1 is attained in visible light over the nanocomposite without cocatalyst, 5.5-fold and 3.4-fold improvement over that of discrete Sb2O3 and W18O49 respectively, which also significantly exceeds many previous reported photocatalytic systems. The superior photocatalytic performance can be attributed to the unique structure of the composites, which provides ample exposed surface catalytic sites with a high density of oxygen vacancies, promoting the adsorption and activation of N2 molecules to form *NNH. Equally importantly, the interface between Sb2O3 and W18O49 greatly facilitates charge carrier migration and separation. Further density functional theory calculations manifest that the interfacial metal sites on Sb2O3/W18O49 serve as the main active centers which possess a strong donating electron ability to the empty N2 antibonding orbitals to trigger the following NH3 synthesis. This work provides a simple and effective method to modify metal oxides for enhancing N2 photofixation.