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The structural evolution of local coordination environments of single-atom catalysts (SACs) under reaction conditions plays an important role in the catalytic performance of SACs. Using density functional theory calculations, the possible structural evolution of transition metal single atoms supported by B/N codoped-graphene (TM-B 2 N 2 /G) under nitrogen reduction reaction (NRR) conditions is explored and the catalytic performance based on reconstructed SACs is theoretically evaluated. A novel nitrogen adsorption mode on TM-B 2 N 2 /G is discovered and the protonation of one of the N atoms results in the TM atoms binding with three N atoms, among which one associates with two B atoms (TM-N 3 B 2 /G). It is suggested that the N 3 B 2 /G supported tungsten single atom (W-N 3 B 2 /G) exhibits excellent N 2 activity with a limiting potential of -0.27 V and high ammonia selectivity. Electronic structure analysis indicates that the coordination of N 3 B 2 /G redistributes the charge density of central W, shifts its d band center upward and strengthens the interaction of W and the adsorbed nitrogen molecule, thereby endowing it with better NRR performance, compared with that supported by pyridine-3N-doped graphene and pyrrolic-3N-doped graphene.

In the present study, a Cu2O@PCz electrode for the nitrogen reduction reaction is proposed; this electrode takes advantage of the catalytic properties of Cu2O in conjunction with conducting polymers such as polycarbazole (PCz). This combination demonstrates an improvement in the catalytic activity and higher stability of this metal oxide in nitrogen electro-reduction reaction (NRR) and nitrogen oxoanion electro-reduction reaction (NORR) processes under aqueous conditions. On this basis, the material synthesized on FTO (SnO2 : F), Cu2O@PCz, exhibits a faradaic efficiency of around 38.83%, together with an NH3 productivity of 1.83 μg h−1 cm−2 in NRR type processes, on applying a potential of −0.8 V (V vs. Ag/AgCl). Similarly, in NORR type processes, the material exhibits NH3 and N2H4 productivity. The latter is the most relevant in terms of the yields obtained. Specifically, using nitrite (NO2−), an efficiency of around 77.72% was obtained, together with a formation rate of 37.02 μg h−1 cm−2 at a potential of −0.8 V (V vs. Ag/AgCl). Although N2H4 is a by-product of ammonia formation, this molecule can be considered an intermediate, which broadens the scope of this study for future research into the production of green chemicals. Finally, this research presents promising new routes for the production of NH3 at room temperature, highlighting the potential of low-cost materials, easy synthesis, and enhanced stability. [ABSTRACT FROM AUTHOR]

Nitric acid is manufactured by oxidizing ammonia where the ammonia comes from an energy demanding and non-eco-friendly, Haber-Bosch process. Electrochemical oxidation of N 2 to nitric acid using renewable electricity could be a promising alternative to bypass the ammonia route. In this work, we discuss the plausible reaction mechanisms of electrochemical N 2 oxidation (N 2 OR) at the molecular level and its competition with the parasitic oxygen evolution reaction (OER). We suggest the design strategies for N 2 oxidation electro-catalysts by first comparing the performance of two catalysts - TiO 2 (110) (poor OER catalyst) and IrO 2 (110) (good OER catalyst), towards dinitrogen oxidation and then establish trends/scaling relations to correlate OER and N 2 OR activities. The challenges associated with electrochemical N 2 OR are highlighted., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

In this study, we present a crystal structure prediction and characterization for two novel single- and double-bonded nitrogen allotropes (denoted as CubN and DobN) bearing three-membered nitrogen cycles. These materials are ambient-pressure metastable robust solids with strong cohesive energies. Due to the presence of strained nitrogen cycles, these allotropes are high-lying phases, which retain high energy densities at least up to 200 GPa, when CubN becomes lower in energy than ζ-N2. The studied allotropes are indirect wide-bandgap semiconductors. A detailed spectral characterization of these materials is also presented herein. Due to their extremely high heats of formation and crystal densities, CubN and DobN demonstrate excellent detonation properties that are comparable to those of previously reported phases (cg-N and TrigN). Propulsive properties (including specific impulse and characteristic velocity) of CubN and DobN as solid monopropellants were also estimated. Thus, if synthesized, the present nitrogen allotropes will have great potential for practical applications and achieving fundamental knowledge about nitrogen as a chemical element.

We compute molecular continuum orbitals in the single center expansion scheme. We then employ these orbitals to obtain molecular Auger rates and single-photon ionization cross sections to study the interaction of N 2 with Free-Electron-Laser (FEL) pulses. The nuclei are kept fixed. We formulate rate equations for the energetically allowed molecular and atomic transitions and we account for dissociation through additional terms in the rate equations. Solving these equations for different parameters of the FEL pulse, allows us to identify the most efficient parameters of the FEL pulse for obtaining the highest contribution of double core hole states (DCH) in the final atomic ion fragments. Finally we identify the contribution of DCH states in the electron spectra and show that the DCH state contribution is more easily identified in the photo-ionization rather than the Auger transitions.

We present an extensive theoretical study of N 2 adsorption mechanisms on an Fe(111) surface. We combine the static analysis of a six-dimensional potential energy surface (6D-PES), based on ab initio density functional theory (DFT) calculations for the system, with quasi-classical trajectory (QCT) calculations to simulate the adsorption dynamics. There are four molecular adsorption states, usually called γ, δ, α, and ε, arising from our DFT calculations. We find that N 2 adsorption in the γ-state is non-activated, while the threshold energy is associated with the entrance channel for the other three adsorption states. Our QCT calculations confirm that there are activated and nonactivated paths for the adsorption of N 2 on the Fe(111) surface, which is in agreement with previous experimental investigations. Molecular dynamics at a surface temperature T s = 300 K and impact energies E i in the 0-5 eV range show the relative occupancy of the γ, δ, α, and ε states. The δ-state, however, is only marginally populated despite its adsorption energy being very similar to that of the γ-state. Our QCT calculations trace the dependence of molecular trapping on the surface temperature T s and initial impact energy E i and quantify the rates of the different competitive channels that eventually lead to molecular adsorption.

The efficient synthesis of ammonia using carbon-footprint-free hydrogen under mild conditions is a grand challenge in chemistry today. To achieve this objective, novel concepts are needed for the activation process and catalyst. This article briefly reviews catalytic activation of N2 for ammonia synthesis under mild conditions. The features of the various activation methods reported so far are summarized, looking chronologically back at progress in heterogeneous catalysts since the use of iron oxide for the Haber–Bosch process, and finally the technical challenges to be overcome are described. Establishing low work functions for the support materials of the metal catalysts is one key to reducing the activation barrier to dissociate N2. Surfaces of electride materials that preserve the character of the bulk are shown to be useful for this purpose. The requirements of desired catalysts are high efficiency at low temperatures, Ru-free compositions, and chemical robustness in the ambient atmosphere. [ABSTRACT FROM AUTHOR]

Denitrification and anaerobic ammonium oxidation (anammox) are important biological processes of the nitrogen cycle that help to preserve the global ecosystem. However, indiscriminate development and global population growth result in the discharge of large amounts of nitrogen species (e.g., via the Haber–Bosch process), particularly nitrogen oxides and ammonia, which cannot be fully digested by microorganisms and therefore accumulate in soil and water. Photocatalysts can promote the conversion of nitrogen oxides and ammonia to molecular nitrogen under the action of photogenerated electrons and holes, thus mimicking denitrifying and anammox bacteria, respectively. Herein, we review the biomimetic photocatalysts and photoelectrochemical cells used to convert aqueous and airborne nitrogen species to molecular nitrogen and shed light on the charge transfer mechanism that should be selectively controlled to favor the formation of molecular nitrogen over that of nitrogen-containing intermediates and by-products. Last but not least, we discuss the outlooks and perspectives of solar-powered molecular nitrogen recovery and suggest guidelines for the design of high-performance denitrification/anammox bacteria-like photocatalysts. [ABSTRACT FROM AUTHOR]

Nitrogen-containing multi-wall carbon nanotubes (N-MWCNTs) were synthesized using aerosol assisted chemical vapor deposition (CVD) techniques in conjunction with benzylamine:ferrocene or acetonitrile:ferrocene mixtures. Different amounts of toluene were added to these mixtures in order to change the N/C ratio of the feedstock. X-ray photoelectron and near-edge X-ray absorption fine structure spectroscopy detected pyridinic, pyrrolic, graphitic, and molecular nitrogen forms in the N-MWCNT samples. Analysis of the spectral data indicated that whilst the nature of the nitrogen-containing precursor has little effect on the concentrations of the different forms of nitrogen in N-MWCNTs, the N/C ratio in the feedstock appeared to be the determining factor. When the N/C ratio was lower than ca. 0.01, all four forms existed in equal concentrations, for N/C ratios above 0.01, graphitic and molecular nitrogen were dominant. Furthermore, higher concentrations of pyridinic nitrogen in the outer shells and N2 molecules in the core of the as-produced N-MWCNTs suggest that the precursors were decomposed into individual atoms, which interacted with the catalyst surface to form CN and NH species or in fact diffused through the bulk of the catalyst particles. These findings are important for a better understanding of possible growth mechanisms for heteroatom-containing carbon nanotubes (CNTs) and therefore paving the way for controlling the spatial distribution of foreign elements in the CNTs using CVD processes.

The ab initio determination of the leading long-range term of pairwise additive dispersive interactions, based on the independent analysis of the response properties of the interacting objects, is here considered in the case where these are part of a periodic system. The interaction of a nitrogen molecule with a thin film of hexagonal BN has been chosen as a case study for identifying some of the problems involved, and for proposing techniques for their solution. In order to validate the results so obtained, the interaction energy between N(2) and a BN monolayer at different distances has been estimated following a totally different approach, namely by performing post-Hartree-Fock (MP2) supercell calculations using the Crystal+Cryscor suite of programs. The results obtained with the two approaches closely agree over a long range, while the limit of validity of the purely dispersive regime can be clearly assessed.

Nitrogen is often used as an inert background atmosphere in solid state studies of electrode and reaction kinetics, of solid state studies of transport phenomena, and in applications e.g. solid oxide fuel cells (SOFC), sensors and membranes. Thus, chemical and electrochemical reactions of oxides related to or with dinitrogen are not supposed and in general not considered. We demonstrate by a steady state electrochemical polarisation experiments complemented with in situ photoelectron spectroscopy (XPS) that at a temperature of 450 °C dinitrogen can be electrochemically activated at the three phase boundary between N(2), a metal microelectrode and one of the most widely used solid oxide electrolytes--yttria stabilized zirconia (YSZ)--at potentials more negative than E = -1.25 V. The process is neither related to a reduction of the electrolyte nor to an adsorption process or a purely chemical reaction but is electrochemical in nature. Only at potentials more negative than E = -2 V did new components of Zr 3d and Y 3d signals with a lower formal charge appear, thus indicating electrochemical reduction of the electrolyte matrix. Theoretical model calculations suggest the presence of anionic intermediates with delocalized electrons at the electrode/electrolyte reaction interface. The ex situ SIMS analysis confirmed that nitrogen is incorporated and migrates into the electrolyte beneath the electrode.

The reactivity of diatomic titanium with molecular nitrogen has been investigated in rare gas matrices. The formation of Ti2N2 from the condensation of effusive beams of Ti and N2 in neon and argon matrices is observed after sample deposition. Our results also show that the in situ formation results from the spontaneous reaction at 9 K of ground state Ti2 with N2. Several low-lying excited states of Ti2N2 are also observed between 0.78 and 1.1 eV above the ground state, leading to a complex sequence of interacting vibronic transitions, merging into a broad continuum above 1.25 eV. Observations of Ti2(14)N2, Ti2(15)N2 and Ti2(14)N(15)N isotopic data enable the determination of all fundamental vibrations in the ground electronic state. Semi-empirical harmonic potential calculations lead to estimates of 3.22 N cm(-1) for the Ti-N bond force constant and 90 +/- 5 degrees for the bond angles. Comparisons with TiN diatomic data suggest a near square-planar structure with 175 +/- 3 pm TiN bond distance. Quantum chemical calculations at various levels indicate a 1A(g) ground state with a Ti-N distance close to 180 pm and 89 degrees for the NTiN bond angle, and give fundamental frequencies in excellent agreement with the experimentally observed values. Further MRCI calculations on all low-lying states enable an interpretation of the complex electronic spectrum in the NIR region.

The direct molecular simulation (DMS) method is used to obtain shear viscosity data for non-reacting air and its components by simulating isothermal, plane Poiseuille subsonic flows. Shear viscosity is estimated at several temperatures, from 273 K to 10 000 K, by fitting the DMS velocity profiles using the analytic solution of the Navier–Stokes equations for this simple canonical flow. The ab initio potential energy surfaces (PESs) that describe the various atomic-level interactions are the only input in the simulations. Molecules involved in a collision within the flow can occupy any rovibrational state that is allowed by the effective diatomic potential. For molecular nitrogen, oxygen, and air at standard condition molar composition, the DMS shear viscosity predictions are in excellent agreement with the experimental data that are available up to about 2000 K. The results for pure molecular nitrogen and pure molecular oxygen also agree very well with previously published quasi-classical trajectory (QCT) calculations based on the same PESs. It is further shown that the ab initio shear viscosity data are generally lower than the corresponding values used in popular computational fluid dynamics codes, over a wide temperature range. Finally, Wilke's mixing rule is demonstrated to accurately predict the DMS air viscosity results from the pure molecular components data up to 4000 K. [ABSTRACT FROM AUTHOR]

In this article we present a quantitative analysis of the second positive system of molecular nitrogen and the first negative system of the molecular nitrogen cation excited in the presence of ionizing radiation. Optical emission spectra of atmospheric air and nitrogen surrounding 210Po sources were measured from 250 to 400 nm. Multi-Boltzmann and non-Boltzmann vibrational distribution spectral models were used to determine the vibrational temperature and vibrational distribution function of the emitting N2(C³Pu) and N2+(B²S+u) states. A zero-dimensional kinetic model, based on the electron energy distribution function (EEDF) and steady-state excitation and de-excitation of N2(X1S+g), N2 +(B2S+u), N2+(X2S+g), N4+, O2 +, and N2(C3Pu, v), was developed for the prediction of the relative spectral intensity of both the N2+(B2S+u - X2S+ g) emission band and the vibrational bands of N2(C3Pu - B3Pg) for comparison with the experimental data. [ABSTRACT FROM AUTHOR]

The combination of compositional versatility and topological diversity for the integration of electroactive species into high-porosity molecular architectures is perhaps one of the main appeals of metal–organic frameworks (MOFs) in the field of electrocatalysis. This premise has attracted much interest in recent years, and the results generated have also revealed one of the main limitations of molecular materials in this context: low stability under electrocatalytic conditions. Using zirconium MOFs as a starting point, in this work, we use this stability as a variable to discriminate between the most suitable electrocatalytic reaction and specific topologies within this family. Our results revealed that the PCN-224 family is particularly suitable for the electroreduction of molecular nitrogen for the formation of ammonia with faradaic efficiencies above 30% in the presence of Ni2+ sites, an activity that improves most of the catalysts described. We also introduce the fluorination of porphyrin at the meso position as a good alternative to improve both the activity and stability of this material under electrocatalytic conditions. [ABSTRACT FROM AUTHOR]

The ab initiodetermination of the leading long-range term of pairwise additive dispersive interactions, based on the independent analysis of the response properties of the interacting objects, is here considered in the case where these are part of a periodic system. The interaction of a nitrogen molecule with a thin film of hexagonal BN has been chosen as a case study for identifying some of the problems involved, and for proposing techniques for their solution. In order to validate the results so obtained, the interaction energy between N2and a BN monolayer at different distances has been estimated following a totally different approach, namely by performing post-Hartree–Fock (MP2) supercell calculations using the Crystal+Cryscorsuite of programs. The results obtained with the two approaches closely agree over a long range, while the limit of validity of the purely dispersive regime can be clearly assessed. [ABSTRACT FROM AUTHOR]

Chemical transformations of molecular nitrogen (N2), including the nitrogen reduction reaction (NRR), are difficult to catalyze because of the weak Lewis basicity of N2. In this study, it is shown that Lewis acids of the types B(SiR3)3 and B(GeR3)3 bind N2 and CO with anomalously short and strong B–N or B–C bonds. B(SiH3)3·N2 has a B–N bond length of 1.48 Å and a complexation enthalpy of −15.9 kcal mol−1 at the M06-2X/jun-cc-pVTZ level. The selective binding enhancement of N2 and CO is due to π-backbonding from Lewis acid to Lewis base, as demonstrated by orbital analysis and density difference plots. The π-backbonding is found to be a consequence of constructive orbital interactions between the diffuse and highly polarizable B–Si and B–Ge bond regions and the π and π* orbitals of N2. This interaction is strengthened by electron donating substituents on Si or Ge. The π-backbonding interaction is predicted to activate N2 for chemical transformation and reduction, as it decreases the electron density and increases the length of the N–N bond. The binding of N2 and CO by the B(SiR3)3 and B(GeR3)3 types of Lewis acids also has a strong σ-bonding contribution. The relatively high σ-bond strength is connected to the highly positive surface electrostatic potential [VS(r)] above the B atom in the tetragonal binding conformation, but the σ-bonding also has a significant coordinate covalent (dative) contribution. Electron withdrawing substituents increase the potential and the σ-bond strength, but favor the binding of regular Lewis acids, such as NH3 and F−, more strongly than binding of N2 and CO. Molecules of the types B(SiR3)3 and B(GeR3)3 are chemically labile and difficult to synthesize. Heterogenous catalysts with the wanted B(Si–)3 or B(Ge–)3 bonding motif may be prepared by boron doping of nanostructured silicon or germanium compounds. B-doped and hydrogenated silicene is found to have promising properties as catalyst for the electrochemical NRR. [ABSTRACT FROM AUTHOR]

The production of ammonia for agricultural and energy demands has accelerated research for more environmentally-friendly synthesis options, particularly the electrocatalytic reduction of molecular nitrogen (nitrogen reduction reaction, NRR). Catalyst activity for NRR, and selectivity for NRR over the competitive hydrogen evolution reaction (HER), are critical issues for which fundamental knowledge remains scarce. Herein, we present results regarding the NRR activity and selectivity of sputter-deposited titanium nitride and titanium oxynitride films for NRR and HER. Electrochemical, fluorescence and UV absorption measurements show that titanium oxynitride exhibits NRR activity under acidic conditions (pH 1.6, 3.2) but is inactive at pH 7. Ti oxynitride is HER inactive at all these pH values. In contrast, TiN – with no oxygen content upon deposition – is both NRR and HER inactive at all the above pH values. This difference in oxynitride/nitride reactivity is observed despite the fact that both films exhibit very similar surface chemical compositions – predominantly TiIV oxide – upon exposure to ambient, as determined by ex situ X-ray photoelectron spectroscopy (XPS). XPS, with in situ transfer between electrochemical and UHV environments, however, demonstrates that this TiIV oxide top layer is unstable under acidic conditions, but stable at pH 7, explaining the inactivity of titanium oxynitride at this pH. The inactivity of TiN at acidic and neutral pH is explained by DFT-based calculations showing that N2 adsorption at N-ligated Ti centers is energetically significantly less favorable than at O-ligated centers. These calculations also predict that N2 will not bind to TiIV centers due to a lack of π-backbonding. Ex situ XPS measurements and electrochemical probe measurements at pH 3.2 demonstrate that Ti oxynitride films undergo gradual dissolution under NRR conditions. The present results demonstrate that the long-term catalyst stability and maintenance of metal cations in intermediate oxidation states for pi-backbonding are critical issues worthy of further examination. [ABSTRACT FROM AUTHOR]

The reaction N(4S) + NO(X2Π) → O(3P) + N2(X1Σ +g) plays a pivotal role in the conversion of atomic to molecular nitrogen in dense interstellar clouds and in the atmosphere. Here we report a joint experimental and computational investigation of the N + NO reaction with the aim of providing improved constraints on its low temperature reactivity. Thermal rates were measured over the 50 to 296 K range in a continuous supersonic flow reactor coupled with pulsed laser photolysis and laser induced fluorescence for the production and detection of N(4S) atoms, respectively. With decreasing temperature, the experimentally measured reaction rate was found to monotonously increase up to a value of (6.6 ± 1.3) × 10−11 cm3 s−1 at 50 K. To confirm this finding, quasi-classical trajectory simulations were carried out on a previously validated, full-dimensional potential energy surface (PES). However, around 50 K the computed rates decreased which required re-evaluation of the reactive PES in the long-range part due to a small spurious barrier with a height of ∼40 K in the entrance channel. By exploring different correction schemes the measured thermal rates can be adequately reproduced, displaying a clear negative temperature dependence over the entire temperature range. The possible astrochemical implications of an increased reaction rate at low temperature are also discussed. [ABSTRACT FROM AUTHOR]

Aside from the desulfurisation, the denitrogenation of fuels is of great importance to minimze the environmental impact of transport emissions. The oxidative reaction pathway of organic nitrogen in the catalytic oxidative denitrogenation could be successfully elucidated. This is the first time such a pathway could be traced in detail in non-microbial systems. It was found that the organic nitrogen is first oxidized to nitrate, which is subsequently reduced to molecular nitrogen via nitrous oxide. Hereby, the organic substrate serves as a reducing agent. The discovery of this pathway is an important milestone for the further development of fuel denitrogenation technologies. [ABSTRACT FROM AUTHOR]

We report a combined experimental and theoretical study dedicated to analyze the N 1s core-level binding energies (CLBE) in N-doped carbon nanotubes (N-CNTs). X-ray photoelectron spectroscopy (XPS) data are obtained from N-CNT samples synthesized using the chemical vapor deposition technique. Extensive density functional theory (DFT) calculations are performed on various model single- and double-walled N-CNTs where N 1s CLBEs are determined using Koopman's theorem. However, we also present additional calculations within the (Z + 1) approximation to analyze the role of final-state effects. From XPS data up to 2 at% of N content was found in our samples and the high resolution analysis of the N 1s line shows, according to previous experimental results, that N species exist in CNTs as graphitic, pyrrolic, pyridinic, and molecular configurations. However, peak decomposition is characterized by five broad Gaussian curves that overlap considerably among them, having different widths and heights, implying a more complex distribution of N atoms within the structures. DFT calculations performed on model N-CNTs reveal a strong dependence of N 1s CLBE values and their shifts on the local atomic environment. Different types of graphitic N cover an energy range of 3 eV, while various configurations for pyridinic, pyrrolic, and molecular species reveal a dispersion in their energy values of 5.7, 2.7, and 5.2 eV, respectively. The previous distributions of theoretical CLBEs also strongly overlap, implying that some peaks in the XPS spectra must be understood as composite signals where the signals of different N defects coexist. We find, in agreement with the experimental data, that freestanding molecular nitrogen and (weakly interacting) encapsulated N2 within the hollow core of model CNTs have very similar CLBEs. Furthermore, we predict that chemisorbed N2 on defective regions of the nanotube walls has N 1s binding energy values that are considerably larger when compared to encapsulated N2, thus making possible their identification. In contrast to previous reports, we find a nontrivial dependence between CLBEs and the local electronic occupation at N sites. The assignment of spectral details in the XPS data to well-defined N-defects on CNTs is not straightforward and needs to be more deeply analyzed. [ABSTRACT FROM AUTHOR]

The activation and transformation of molecular nitrogen (N2) by metal hydride species has attracted widespread attention due to its critical role in nitrogen fixation. Herein, the reactions between tantalum deuteride cluster anions Ta2D2,4− and N2 were investigated experimentally and theoretically. An unprecedented reaction channel of the liberation of a single D atom was observed and much superior reactivity was identified for Ta2D4−. Theoretical investigations indicate that the releasing of D atoms benefits from the completely dissociative adsorption of N2 on the dinuclear metal centres. The extra D atoms in Ta2D4− compared to Ta2D2− are helpful to create sufficient electron density at the adsorption site and modify the symmetry of active orbitals to facilitate a further reduction of N2. This comparative study provides a molecular-level insight to understand the high structure-modulating capability of the additional hydride ligands in polyhydride species in the adsorption and activation of nitrogen molecules. [ABSTRACT FROM AUTHOR]

Mild-condition nitrogen fixation using “green” solar energy, merely requiring a solar-to-NH3 (STA) efficiency of 0.1% for potential use, is a promising alternative to the Haber–Bosch process but remains a great challenge. The bottleneck lies in the ultra-low efficiency originating from the sluggish surface reaction involving 6e−/6H+, specifically, the rate-limiting reductive activation of nitrogen. To meet this challenge, a common approach adopted by natural nitrogenase or artificial catalysts is to craft an active center (transition metal) of electron-rich nature, thus enriching the LUMO (lowest unoccupied molecular orbital) electron density of N2via the e−→π*-orbital (N) transition to facilitate the molecular nitrogen activation. Recent progress suggests that anion vacancies such as O, C, N, and S vacancies, which inherently bear excess electrons and coordinatively unsaturated metal ions, could be explored in promoting the molecular nitrogen activation in photocatalysis. In this review, we summarize the in depth anion vacancy-dominated nitrogen photo-fixation systems, and then focus on the mechanical understanding of how an anion vacancy kinetically affects the nitrogen reductive activation including N–N triple bond weakening, N2 adsorption and activation energies, and kinetic pathways, and finally propose the future challenges and prospects of this emerging area. [ABSTRACT FROM AUTHOR]

Photo-driven nitrogen fixation involves the activation and hydrogenation processes of molecular nitrogen in producing ammonia at the photocatalyst surface. Herein, significant enhancement of the catalytic efficiency is achieved via constructing a ternary Ag/PW10V2/am-TiO2−x composite (the optimal PW10V2 and Ag NPs loadings are 14.5 wt% and 1.5 wt%, respectively) with high specific surface area of 513 m2 g−1. The well-designed Z-scheme heterojunction between divanadium substituted phosphotungstic acid (PW10V2) and amorphous TiO2−x (am-TiO2−x) combined with localized surface plasmon resonance (LSPR) of Ag NPs endowed the ternary Ag/PW10V2/am-TiO2−x composite with superior oxidation–reduction performance. Accommodated by amorphization and defect engineering, enriched surface oxygen vacancies (OVs) were produced. In the absence of a sacrificial agent, high NH3/NH4+ productions of 424.9 μmol gcat−1 were achieved under a nitrogen atmosphere when irradiating under simulated sunlight for 2 h. The results show that the enhancement of catalytic efficacy is well correlated with a Z-scheme heterojunction and Ag–am-TiO2−x interface with factors of 1.2–1.4 and 1.4–1.8, respectively. The roles of the surface OVs and amorphous structure are emphasized when compared with anatase TiO2−x and Ag/PW10V2/anatase-TiO2−x. In addition to the excellent photocatalytic activity, the composite demonstrates high photochemical stability with negligible activity decay. This work also gives some inspiration to prepare polyoxometalates-based photocatalysts with high activity for photocatalytic nitrogen fixation. [ABSTRACT FROM AUTHOR]