Ab-initio insights into the mechanical, phonon, bonding, electronic, optical and thermal properties of hexagonal W2N3 for prospective applications.

We thoroughly investigated the structural, mechanical, electronic, vibrational, optical, thermodynamic, and a number of thermophysical properties of W2N3 compound through first-principles calculations using the DFT based formalism. The calculated structural parameters show very good agreement with the available theoretical and experimental results. The mechanical and dynamical stabilities of this compound have been investigated theoretically from the elastic constants and phonon dispersion curves. The Pugh's and Poisson's ratios of W2N3 are located quite close to the brittle/ductile borderline. W2N3 is elastically anisotropic. The calculated electronic band structure and density of states reveal that W2N3 is conducting in nature. The Fermi surface topology has also been explored. The analysis of charge density distribution map shows that W atoms have comparatively high electron density around compared to the N atoms. Presence of covalent bondings between W-N, W-W, and N-N atoms are anticipated. High melting temperature and high phonon thermal conductivity of W2N3 imply that the compound has potential to be used as a heat sink system. The optical characteristics show anisotropy. The compound can be used in optoelectronic devices due to its high absorption coefficient and low reflectivity in the visible to ultraviolet spectrum. Furthermore, the quasi-harmonic Debye model is used to examine temperature and pressure dependent thermal characteristics of W2N3 for the first time.

Designing core-shell heterostructure arrays based on snowflake NiCoFe-LTH shelled over W2N-WC nanowires as an advanced bi-functional electrocatalyst for boosting alkaline water/seawater electrolysis.

The pursuit of efficient and sustainable hydrogen production through water splitting has led to intensive research in the field of electrocatalysis. However, the impediment posed by sluggish reaction kinetics has served as a significant barrier. This challenge has inspired the development of electrocatalysts characterized by high activity, abundance in earth's resources, and long-term stability. In addressing this obstacle, it is imperative to meticulously fine-tune the structure, morphology, and electronic state of electrocatalysts. By systematically manipulating these key parameters, the full potential of electrocatalysts can unleash, enhancing their catalytic activity and overall performance. Hence in this study, a novel heterostructure is designed, showcasing core-shell architectures achieved by covering W2N-WC nanowire arrays with tri-metallic Nickel-Cobalt-Iron layered triple hydroxide nanosheets on carbon felt support (NiCoFe-LTH/W2N-WC/CF). By integrating the different virtue such as binder free electrode design, synergistic effect between different components, core-shell structural advantages, high exposed active sites, high electrical conductivity and heterostructure design, NiCoFe-LTH/W2N-WC/CF demonstrates striking catalytic performances under alkaline conditions. The substantiation of all the mentioned advantages has been validated through electrochemical data in this study. According to these results NiCoFe-LTH/W2N-WC/CF achieves a current density of 10 mA cm-2 needs overpotential values of 101 mV for HER and 206 mV for OER, respectively. Moreover, as a bi-functional electrocatalyst for overall water splitting, a two-electrode device needs a voltage of 1.543 V and 1.569 V to reach a current density of 10 mA cm-2 for alkaline water and alkaline seawater electrolysis, respectively. Briefly, this research with attempting to combination of different factors try to present a promising stride towards advancing bi-functional catalytic activity with tailored architectures for practical green hydrogen production via electrochemical water splitting process.

Interface engineering and nanoconfinement strategies to synergistically enhance hydrogen evolution in acidic and basic media.

As a potential catalyst for hydrogen evolution reaction (HER), tungsten nitride (W2N) has attracted extensive attention, due to its Pt-like characteristic. Nevertheless, insufficient active sites, slow electron transfer, and lack of scale-up nano-synthesis methods significantly limit its practical application. Constructing multi-component active centers and interface-rich heterojunctions to increase exposed active sites and modulate interface electrons is a very effective modification strategy. Therefore, a nano-heterostructure formed from tungsten nitride, tungsten phosphide and tungsten encapsulated in N, P co-doped carbon nanofiber (W2N/WP/W@NPC) was synthesized by a flexible and scalable electrospinning technology. Experimental results reveal that abundant heterojunctions are formed, electron transfer occurs between tungsten nitride and tungsten phosphide, and carbon nanofibers play a confinement role. The optimized W2N/WP/W@NPC-3 electrocatalyst demonstrates excellent HER catalytic activity and robust stability in both acidic and base media. Furthermore, the overall water splitting performance is tested using W2N/WP/W@NPC as the cathode through a two-electrode electrolyzer, which also exhibits impressive electrochemical performance.

Confined VLS Growth of Single-Layer 2D Tungsten Nitrides.

Two-dimensional (2D) metal nitrides have garnered significant interest due to their potential applications in future electronics and quantum systems. However, the synthesis of such materials with sufficient uniformity and at relevant scales remains an unaddressed challenge. This study demonstrates the potential of confined growth to control and enhance the morphology of 2D metal nitrides. By restricting the reaction volume of vapor-liquid-solid reactions, an enhanced precursor concentration was achieved that reduces the nucleation density, resulting in larger grain sizes and suppression of multilayer growth. Detailed characterization reveals the importance of balancing the energetic and kinetic aspects of tungsten nitride formation toward this ability. The introduction of a promoter enabled the realization of large-scale, single-layer tungsten nitride with a uniform and high interfacial quality. Finally, our advance in morphology control was applied to the production of edge-enriched 2D tungsten nitrides with significantly enhanced hydrogen evolution ability, as indicated by an unprecedented Tafel slope of 55 mV/dec.

Tungsten Nitride (W5N6): An Ultraresilient 2D Semimetal.

Two-dimensional transition metal nitrides offer intriguing possibilities for achieving novel electronic and mechanical functionality owing to their distinctive and tunable bonding characteristics compared to other 2D materials. We demonstrate here the enabling effects of strong bonding on the morphology and functionality of 2D tungsten nitrides. The employed bottom-up synthesis experienced a unique substrate stabilization effect beyond van-der-Waals epitaxy that favored W5N6 over lower metal nitrides. Comprehensive structural and electronic characterization reveals that monolayer W5N6 can be synthesized at large scale and shows semimetallic behavior with an intriguing indirect band structure. Moreover, the material exhibits exceptional resilience against mechanical damage and chemical reactions. Leveraging these electronic properties and robustness, we demonstrate the application of W5N6 as atomic-scale dry etch stops that allow the integration of high-performance 2D materials contacts. These findings highlight the potential of 2D transition metal nitrides for realizing advanced electronic devices and functional interfaces.

Tungsten Nitride/Tungsten Oxide Nanosheets for Enhanced Oxynitride Intermediate Adsorption and Hydrogenation in Nitrate Electroreduction to Ammonia.

Electrochemical NO3- reduction reaction (NO3RR) is a promising technique for green NH3 synthesis. Tungsten oxide (WO3) has been regarded as an effective electrocatalyst for electrochemical NH3 synthesis. However, the weak adsorption and the sluggish hydrogenation of oxynitride intermediates (NOx, e.g., *NO3 and *NO2) over WO3 materials hinder the efficiency of converting NO3- to NH3. Herein, we design a heterostructure of tungsten nitride (WN) and WO3 (WN/WO3) nanosheets to optimize *NO3 and *NO2 adsorptions and facilitate *NO2 hydrogenations to achieve a highly efficient electrochemical NO3RR to produce NH3. Theoretical calculations predict that locally introducing WN into WO3 will shorten the distance between adjacent W atoms, resulting in *NO3 and *NO2 being strongly adsorbed on W active sites in the form of bidentate ligands instead of the relatively weak monodentate ligands. Furthermore, WN facilitates H2O dissociation to supply the requisite protons, which is beneficial for *NO2 hydrogenations. Inspired by theoretical prediction, WN/WO3 nanosheets are successfully fabricated through a high-temperature nitridation process. The transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray absorption near-edge spectroscopy investigations confirm that the amorphous WN has been locally introduced in situ into WO3 nanosheets to form a composite heterostructure. The as-prepared WN/WO3 nanosheets exhibit a high Faraday efficiency of 88.9 ± 7.2% and an appreciable yield rate of 8.4 mg h-1 cm-2 toward NH3 production, which is much higher than that of individual WO3 and WN. The enhanced adsorption and hydrogenation behaviors of *NOx over WN/WO3 are characterized by in situ Fourier-transform infrared spectroscopy, consistent with the theoretical predictions. This work develops facile and effective heterostructure nanomaterials to tune the adsorption and hydrogenation of NOx for boosting the efficiency from NO3- to NH3.

Directly Sputtered Molybdenum Disulfide Nanoworms Decorated with Binder-less VN and W2N Nanoarrays for Bendable Large-Scale Asymmetric Supercapacitor.

Considering the superior capacitive performance and rich redox kinetics, the two-dimensional (2D) layered molybdenum disulfide (MoS2) and transition metal nitrides (TMNs) have emerged as the latest set of nanomaterials. Direct incorporation of key materials vanadium nitride (VN) and tungsten nitride (W2N) into a MoS2 array has been achieved on cost-effective, bendable stainless steel (SS) foil via a reactive cosputtering route. Herein, we have utilized the synergistic effect of intermixed nanohybrids to develop a flexible asymmetric supercapacitor (FASC) device from MoS2-VN@SS (negative) and MoS2-W2N@SS (positive) electrodes. As-constructed FASC cell possesses a maximum operational potential of 1.80 V and an exceptional gravimetric capacitance of 200 F g-1 at a sweep rate of 5 mV s-1. The sustained capacitive performance mainly accounts for the synergism induced through unique interfacial surface architecture provided by MoS2 nanoworms and TMN conductive hosts. The sulfur and nitrogen edges ensure the transport channels to Li+/SO4-2 ions for intercalation/deintercalation into the composite nanostructured thin film, further promoting the pseudocapacitive behavior. Consequently, the supercapacitor cell exhibits a distinctive specific energy of 87.91 Wh kg-1 at 0.87 kW kg-1 specific power and a reduced open circuit potential (OCP) decay rate (∼42% self-discharge after 60 min). Moreover, the assembled flexible device exhibits nearly unperturbed electrochemical response even at bending at 165° angle and illustrates a commendable cyclic life-span of 82% after 20,000 charge-discharge cycles, elucidating advanced mechanical robustness and capacitance retentivity. The powering of a multicolor light-emitting diode (LED) and electronic digital watch facilitates the practical evidence to open up possibilities in next-generation state-of-the-art wearable and miniaturized energy storage systems.

In Situ Surface Restraint-Induced Synthesis of Transition-Metal Nitride Ultrathin Nanocrystals as Ultrasensitive SERS Substrate with Ultrahigh Durability.

It is a major challenge to synthesize crystalline transition-metal nitride (TMN) ultrathin nanocrystals due to their harsh reaction conditions. Herein, we report that highly crystalline tungsten nitride (W2N, WN, W3N4, W2N3) nanocrystals with small size and excellent dispersibility are prepared by a mild and general in situ surface restraint-induced growth method. These ultrafine tungsten nitride nanocrystals are immobilized in ultrathin carbon layers, forming an interesting hybrid nanobelt structure. The hybrid WN/C nanobelts exhibit a strong localized surface plasmon resonance (LSPR) effect and surface-enhanced Raman scattering (SERS) effect, including a lowest detection limit of 1 × 10-12 M and a Raman enhancement factor of 6.5 × 108 comparable to noble metals, which may be one of the best records for non-noble metal SERS substrates. Moreover, they even can maintain the SERS performance in a variety of harsh environments, showing outstanding corrosion resistance, radiation resistance, and oxidation resistance, which is not available on traditional noble metal and semiconductor SERS substrates. A synergistic Raman enhancement mechanism of LSPR and interface charge transfer is found in the carbon-coated tungsten nitride substrate. A microfluidic SERS channel integrating the enrichment and detection of trace substances is constructed with the WN/C nanobelt, which realizes high-throughput dynamic SERS analysis.

A high efficiency water hydrogen production method based on CdS/WN composite photocatalytic.

Based on the strategy that electrocatalysts can be used as additives to improve the performance of photocatalysts, and the unique metalloid properties of tungsten nitride (WN), it can form a Schottky junction with the semiconductor at the heterogeneous interface to improve the photocatalytic performance of semiconductor catalysts. In this paper, WN with excellent electrical conductivity was selected as a new noble-metal-free co-catalyst to improve the photoreduction hydrogen (H2) evolution performance of CdS nanoparticles (NPs). Firstly, WN nanosheets were prepared by sol-gel method; then, a novel and noble-metal-free heterojunction photocatalyst, which is CdS NPs deposited on the surface of WN, was successfully fabricated via one-pot solvothermal method. Under visible light irradiation, the H2 production rate of the WN/CdS composite catalyst is 24.13 mmol/g/h, which is 9.28 times that of pure CdS NPs. The observably boosted H2 generation activity could be ascribed to the broadened visible-light absorption and intimate interfacial contact between CdS NPs and WN engenders Schottky junction. This study provides a novel and cost-effective approach for designing efficient noble-metal-free photocatalysts and improving H2 evolution activity of CdS under visible-light-driven photocatalytic water splitting.

Plasmonic Enhanced Reactive Oxygen Species Activation on Low-Work-Function Tungsten Nitride for Direct Near-Infrared Driven Photocatalysis.

Realizing near-infrared (NIR) driven photocatalytic reaction is one of the promising strategies to promote the solar energy utilization and photocatalytic efficiencies. However, effective reactive oxygen species (ROS) activation under NIR irradiation remains to be great challenge for nearly all previously reported photocatalysts. Herein, the cubic-phase tungsten nitride (WN) with strong plasmonic NIR absorption and low-work function (≈3.59 eV) is proved to be able to mediate direct ROS activation by both of experimental observation and theoretical simulation. The cubic WN nanocubes (NCs) are synthesized via the hydrothermal-ammonia nitridation process and its NIR-driven photocatalytic properties, including photocatalytic degradation, hydroxylation, and de-esterification, are reported for the first time in this work. The 3D finite element simulation results demonstrate the size dependent and wavelength tuned plasmonic NIR absorption of the WN NCs. The NIR-driven photocatalytic mechanism of WN NCs is proposed based on density functional theory (DFT) calculated electronic structure and facet dependent O2 (or H2 O) molecular activation, radicals scavenging test, spin trapped electron paramagnetic resonance measurements, and ultraviolet photoelectronic spectrum (UPS). Overall, the results in this work pave a way for the application of low-work-function materials as highly reactive NIR photocatalyst.

Bandgap-Tuned 2D Boron Nitride/Tungsten Nitride Nanocomposites for Development of High-Performance Deep Ultraviolet Selective Photodetectors.

This study presents a fast and effective method to synthesize 2D boron nitride/tungsten nitride (BN-WN) nanocomposites for tunable bandgap structures and devices. A few minutes of synthesis yielded a large quantity of high-quality 2D nanocomposites, with which a simple, low-cost deep UV photo-detector (DUV-PD) was fabricated and tested. The new device was demonstrated to have very good performance. High responsivity up to 1.17 A/W, fast response-time of lower than two milliseconds and highly stable repeatability were obtained. Furthermore, the influences of operating temperature and applied bias voltage on the properties of DUV-PD as well as its band structure shift were investigated.

Tungsten Nitride, Well-Dispersed on Porous Carbon: Remarkable Catalyst, Produced without Addition of Ammonia, for the Oxidative Desulfurization of Liquid Fuel.

Polyanilines (pANIs), loaded with phosphotungstic acid (PTA), are pyrolyzed to get WO3 or W2 N (≈6 and ≈7 nm, respectively), which is well-dispersed on pANI-derived porous carbons (pDCs). Depending on the pyrolysis temperature, WO3 /pDC, W2 N/pDC, or W2 N-W/pDCs could be obtained selectively. pANI acts as both the precursor of pDC and the nitrogen source for the nitridation of WO3 into W2 N during the pyrolysis. Importantly, W2 N could be obtained from the pyrolysis without ammonia feeding. The obtained W2 N/pDC is applied as a heterogeneous catalyst for the oxidative desulfurization (ODS) of liquid fuel for the first time, and the results are compared with WO3 /pDC and WO3 /ZrO2 . The W2 N/pDC is very efficient in ODS with remarkable performance compared with WO3 /pDC or WO3 /ZrO2 , which is applied as a representative ODS catalyst. For example, W2 N/pDC shows around 3.4 and 2.7 times of kinetic constant and turnover frequency (based on 5 min of reaction), respectively, compared to that of WO3 /ZrO2 . Moreover, the catalysts could be regenerated in a facile way. Therefore, W2 N/pDC could be produced facilely from pyrolysis (without ammonia feeding) of PTA/pANI, and W2 N, well-dispersed on pDC, can be suggested as a very efficient oxidation catalyst for the desulfurization of liquid fuel.

Sulfur in Mesoporous Tungsten Nitride Foam Blocks: A Rational Lithium Polysulfide Confinement Experimental Design Strategy Augmented by Theoretical Predictions.

To enhance the utilization of sulfur in lithium-sulfur batteries, three-dimensional tungsten nitride (WN) mesoporous foam blocks are designed to spatially localize the soluble Li2S6 and Li2S4 within the pore spaces. Meanwhile, the chemisorption behaviors of polysulfides and the capability of WN as an effective confiner are systematically investigated through density functional theory calculations and experimental studies. The theoretical calculations reveal a decrease in chemisorption strength between WN and the soluble polysulfides (Li2S8 > Li2S6 > Li2S4), while the interactions between WN and the insoluble Li2S2/Li2S show a high chemisorption strength of ca. 3 eV. Validating theoretical insights through electrochemical measurements further manifest that the assembled battery configurations with sulfur cathode confined in the thickest WN blocks exhibit the best rate capabilities (1090 and 510 mAh g-1 at 0.5C and 5C, respectively) with the highest initial Coulombic efficiency of 90.5%. Moreover, a reversible capacity of 358 mAh g-1 is maintained with a high Coulombic efficiency approaching to 100%, even after 500 cycles at 2C. As guided by in silico design, this work not only provides an effective strategy to improve the retentivity of polysulfides but also underpins that properly architectured WN can be effective retainers of polysulfides.

Rationally Designed Hierarchically Structured Tungsten Nitride and Nitrogen-Rich Graphene-Like Carbon Nanocomposite as Efficient Hydrogen Evolution Electrocatalyst.

Practical application of hydrogen production from water splitting relies strongly on the development of low-cost and high-performance electrocatalysts for hydrogen evolution reaction (HER). The previous researches mainly focused on transition metal nitrides as HER catalysts due to their electrical conductivity and corrosion stability under acidic electrolyte, while tungsten nitrides have reported poorer activity for HER. Here the activity of tungsten nitride is optimized through rational design of a tungsten nitride-carbon composite. More specifically, tungsten nitride (WN x ) coupled with nitrogen-rich porous graphene-like carbon is prepared through a low-cost ion-exchange/molten-salt strategy. Benefiting from the nanostructured WN x , the highly porous structure and rich nitrogen dopant (9.5 at%) of the carbon phase with high percentage of pyridinic-N (54.3%), and more importantly, their synergistic effect, the composite catalyst displays remarkably high catalytic activity while maintaining good stability. This work highlights a powerful way to design more efficient metal-carbon composites catalysts for HER.

A novel superhard tungsten nitride predicted by machine-learning accelerated crystal structure search.

Transition metal nitrides have been suggested to have both high hardness and good thermal stability with large potential application value, but so far stable superhard transition metal nitrides have not been synthesized. Here, with our newly developed machine-learning accelerated crystal structure searching method, we designed a superhard tungsten nitride, h-WN6, which can be synthesized at pressure around 65 GPa and quenchable to ambient pressure. This h-WN6 is constructed with single-bonded armchair-like N6 rings and presents ionic-like features, which can be formulated as W2.4+N62.4-. It has a band gap of 1.6 eV at 0 GPa and exhibits an abnormal gap broadening behavior under pressure. Excitingly, this h-WN6 is found to be the hardest among transition metal nitrides known so far (Vickers hardness around 57 GPa) and also has a very high melting temperature (around 1,900 K). Additionally, the good gravimetric (3.1 kJ/g) and volumetric (28.0 kJ/cm3) energy densities make this nitrogen-rich compound a potential high-energy-density material. These predictions support the designing rules and may stimulate future experiments to synthesize superhard and high-energy-density material.

Black Tungsten Nitride as a Metallic Photocatalyst for Overall Water Splitting Operable at up to 765†nm.

Semiconductor photocatalysts are hardly employed for overall water splitting beyond 700 nm, which is due to both thermodynamic aspects and activation barriers. Metallic materials as photocatalysts are known to overcome this limitation through interband transitions for creating electron-hole pairs; however, the application of metallic photocatalysts for overall water splitting has never been fulfilled. Black tungsten nitride is now employed as a metallic photocatalyst for overall water splitting at wavelengths of up to 765 nm. Experimental and theoretical results together confirm that metallic properties play a substantial role in exhibiting photocatalytic activity under red-light irradiation for tungsten nitride. This work represents the first red-light responsive photocatalyst for overall water splitting, and may open a promising venue in searching of metallic materials as efficient photocatalysts for solar energy utilization.