Nitrogen vacancies enriched Ce-doped Ni_(3)N hierarchical nanosheets triggering highly-efficient urea oxidation reaction in urea-assisted energy-saving electrolysis

Urea oxidation reaction (UOR),which has favorable thermodynamic energy barriers compared with oxygen evolution reaction (OER),can provide more cost-effective electrons for the renewable energy systems,but is trapped by its sluggish UOR kinetics and intricate reaction intermediates formation/desorption process.Herein,we report a novel and effective electrocatalyst consisting of carbon cloth supported nitrogen vacancies-enriched Ce-doped Ni_(3)N hierarchical nanosheets (Ce-Ni_(3)N @CC) to optimize the flat-footed UOR kinetics,especially the stiff rate-determine CO_(2)desorption step of UOR.Upon the introduction of valance state variable Ce,the resultant nitrogen vacancies enriched Ce-Ni_(3)N @CC exhibits an enhanced UOR performance where the operation voltage requires only 1.31 V to deliver the current density of 10 mA cm^(-2),which is superior to that of Ni_(3)N @CC catalyst (1.36 V) and other counterparts.Density functional theory (DFT) results demonstrate that the incorporation of Ce in Ni_(3)N lowers the formation energy of nitrogen vacancies,resulting in rich nitrogen vacancies in Ce-Ni_(3)N @CC.Moreover,the nitrogen vacancies together with Ce doping optimize the local charge distribution around Ni sites,and balance the adsorption energy of CO_(2)in the rate-determining step (RDS),as well as affect the initial adsorption structure of urea,leading to the superior UOR catalytic performance of Ce-Ni_(3)N @CC.When integrating the Ce-Ni_(3)N catalyst in UOR//HER and UOR//CO_(2)R flow electrolyzer,both of them perform well with low operation voltage and robust long-term stability,proofing that the thermodynamically favorable UOR can act as a suitable substitute anodic reaction compared with that of OER.Our findings here not only provide a novel UOR catalyst but also offer a promising design strategy for the future development of energy-related devices.

Biocompatible carbon nitride quantum dots nanozymes with high nitrogen vacancies enhance peroxidase-like activity for broadspectrum antibacterial

Nanozyme antibacterial agents with high enzyme-like catalytic activity and strong bacteria-binding ability have provided an alternative method to efficiently disinfect drug-resistance microorganism.Herein,the carbon nitride quantum dots(CNQDs)nanozymes with high nitrogen vacancies(NVs)were mass-productively prepared by a simple ultrasonic-crushing method assisted by propylene glycol.It was found that the NVs of CNQDs were stemmed from the selective breaking of surface N-(C)_(2)sites,accounting for 6.2%.Experiments and density functional theory(DFT)simulations have demonstrated that the presence of NVs can alter the local electron distribution and extend theπ-electron delocalization to enhance the peroxidase-like activity.Biocompatible CNQDs could enter inside microorganisms by diffusion and elevate the bacteria-binding ability,which enhanced the accurate and rapid attack of·OH to the microorganisms.The sterilization rate of CNQDs against Gram-negative bacteria(E.coli),Gram-positive bacteria(S.aureus,B.subtilis),fungi(R.solani)reaches more than 99%.Thus,this work showed great potential for engineered nanozymes for broad-spectrum antibacterial in biomedicine and environmental protection.

Regulating nitrogen vacancies within graphitic carbon nitride to boost photocatalytic hydrogen peroxide production

Introducing nitrogen vacancies is an effective method to improve the catalytic performance of g-C_(3)N_(4)-based photocatalysts,whereas understanding how nitrogen vacancies types affect the catalytic performance remains unclear.Herein,two different types of nitrogen vacancies were successfully introduced into g-C_(3)N_(4)by pyrolysis of melamine under argon and ammonia atmosphere with subsequent HNO3 oxidation.The pyrolysis atmosphere is found to have a significant influence on the introduced nitrogen vacancies type,where tertiary nitrogen groups(N_(3)C)and sp2-hybridized nitrogen atoms(N_(2)C)were the preferred sites for the formation of nitrogen vacancies under ammonia and argon pyrolysis,respectively.Moreover,nitrogen vacancies from N3C are experimentally and theoretically demonstrated to facilitate the narrowed band gap and the improved oxygen absorption capability.As expected,the optimal catalyst exhibits high H_(2)O_(2)yield of 451.8µM,which is 3.8 times higher than the pristine g-C_(3)N_(4)(119.0µM)after 4 h and good stability after10 photocatalytic runs.

Design of tightly linked dual ring antenna and imaging of magnetic field distribution using a diamond fiber probe

A tightly linked dual ring antenna is designed,and it is specifically tailored for uniformly coupling the microwave magnetic field to the nitrogen-vacancy(NV)center.The designed antenna operates at a center frequency of about 2.87 GHz,with a bandwidth of around 200 MHz,allowing it to address multiple resonance peaks in the optically detected magnetic resonance(ODMR)spectrum in an external magnetic field.Moreover,the antenna generates a fairly uniform magnetic field in a range with a radius of 0.75 mm.High resolution imaging of the magnetic field distribution on the surface of the antenna is conducted by using a fiber diamond probe.We also investigate the effect of magnetic field uniformity on the linewidth of ODMR,so as to provide insights into reducing the inhomogeneous broadening of ODMR.

Metal-Free C_(3)N_(4) with plentiful nitrogen vacancy and increased specific surface area for electrocatalytic nitrogen reduction

As a substitute for synthetic ammonia under mild condition, electrocatalytic nitrogen reduction reaction(NRR) provides a hopeful approach for the development of ammonia. Nevertheless, the current development of NRR electrocatalysts is far from enough and a systematic research is needed to gain a better improvement. This article presents that 2 D C_(3)N_(4)-NV with a large specific surface area and abundant nitrogen vacancies is prepared by a simple and feasible method, and used as a metal-free catalyst for electrocatalytic NRR. Experiment result and density functional theory(DFT) calculation reveal that nitrogen vacancies in 2 D C_(3)N_(4)-NV can act as an efficient active site for catalytic NRR, which is conducive to capturing and activating N_(2), lowering Gibbs free energy(DG) in reaction and inhibiting hydrogen evolution reaction(HER) at the same time. In addition, the larger specific surface area also makes more active site exposed, which is good for the contact between the electrolyte and the active site, thus enhancing its NRR activity. The electrocatalyst shows an excellent catalytic activity for NRR in 0.1 M HCl, including Faradaic efficiency of 10.96%, NH_(3) yields of 17.85 lg h^(-1) mg_(cat)^(-1)., and good stability(over 20 h).

Enhancing anchoring and catalytic conversion of polysulfides by nitrogen deficient cobalt nitride for advanced lithium-sulfur batteries

While lithium-sulfur(Li-S)battery has attracted remarkable attention owing to the high theoretical capacity,its practical application is still hindered by the shuttle and sluggish conversion kinetics of intermediate lithium polysulfides(Li PSs).Defect engineering,which can regulate the electronic structure and in turn influence the surface adsorption and catalytic capability,has been regarded as a feasible strategy to deal with the above challenges.However,few studies on nitrogen vacancies and their mechanisms are reported.Herein,cobalt nitride with nitrogen vacancies grown on multi-walled carbon nanotube(CNTCo N-VN)is designed and applied as the separator modification material to investigate the enhancing mechanism of nitrogen vacancies on Li-S batteries.The experimental evidence and theoretical calculation indicate that the introduction of nitrogen vacancies into cobalt nitride can enhance the chemical affinity to Li PSs and effectively hamper the shuttle effect.Meanwhile the reduced band gap of the d-band center of Co and p-band center of N for CNT-Co N-VNand the promoted diffusion of Li^(+) can expedite the solid-liquid and liquid-liquid conversions of sulfur species.Due to these superiorities,the cell with CNT-Co NVNmodified separator delivers a favorable initial capacity of 901 m Ah g^(-1)and a capacity of 660 m Ah g^(-1)can be achieved after 250 cycles at 2 C.This work explores the application of metal nitride with nitrogen vacancies and sheds light on the development of functional separators for high-efficient Li-S batteries.

Creating nitrogen-vacancy ensembles in diamond for coupling with flux qubit

Hybrid quantum system of negatively charged nitrogen–vacancy（NV^-） centers in diamond and superconducting qubits provide the possibility to extend the performances of both systems. In this work, we numerically simulate the coupling strength between NV^-ensembles and superconducting flux qubits and obtain a lower bound of 1016cm^（-3） for NV^-concentration to achieve a sufficiently strong coupling of 10 MHz when the gap between NV^-ensemble and flux qubit is 0. Moreover, we create NV^-ensembles in different types of diamonds by14^（N＋）and12（C＋）ion implantation, electron irradiation, and high temperature annealing. We obtain an NV^-concentration of 1.05 × 1016cm^（-3） in the diamond with1-ppm nitrogen impurity, which is expected to have a long coherence time for the low nitrogen impurity concentration. This shows a step toward performance improvement of flux qubit-NV^-hybrid system.

Enhancing the electrocatalytic performance of nitrate reduction to ammonia by in-situ nitrogen leaching

Electrochemical nitrate reduction reaction (NITRR) is regarded as a “two birds-one stone” method for the treatment of nitrate contaminant in polluted water and the synthesis of valuable ammonia, which is retarded by the lack of highly reactive and selective electrocatalysts .Herein, for the first time, nickel foam supported Co_(4) N was designed as a high-performance NITRR catalyst by an in-situ nonmetal leaching-induced strategy.At the optimal potential, the Co_(4) N/NF catalyst achieves ultra-high Faraday efficiency and NH_(3) selectivity of 95.4% and 99.4%, respectively.Ex situ X-ray absorption spectroscopy (XAS), together with other experiments powerfully reveal that the nitrogen vacancies produced by nitrogen leaching are stable and play a key role in boosting nitrate reduction to ammonia.Theoretical calculations confirm that Co_(4) N with abundant nitrogen vacancies can optimize the adsorption energies of NO_(3)^(-) and intermediates, lower the free energy (Δ G ) of the potential-determining step (*NH_(3) to NH_(3) ) and inhibit the formation of N-containing byproducts.In addition, we also conclude that the nitrogen vacancies can stabilize the adsorbed hydrogen, making H_(2) quite difficult to produce, and lowering ΔG from *NO to *NOH, which facilitates the selective reduction of nitrate.This study reveals significant insights about the in-situ nonmetal leaching to enhance the NITRR activity.

Surface pseudocapacitance of mesoporous Mo_(3)N_(2) nanowire anode toward reversible high-rate sodium-ion storage

Sodium-ion storage devices are highly desirable for large-scale energy storage applications owing to the wide availability of sodium resources and low cost.Transition metal nitrides(TMNs)are promising anode materials for sodium-ion storage,while their detailed reaction mechanism remains unexplored.Herein,we synthesize the mesoporous Mo3N2 nanowires(Meso-Mo_(3)N_(2)-NWs).The sodium-ion storage mechanism of Mo3N2 is systematically investigated through in-situ XRD,ex-situ experimental characterizations and detailed kinetics analysis.Briefly,the Mo_(3)N_(2) undergoes a surface pseudocapacitive redox charge storage process.Benefiting from the rapid surface redox reaction,the Meso-Mo_(3)N_(2)-NWs anode delivers high specific capacity(282 m Ah g^(-1) at 0.1 A g^(-1)),excellent rate capability(87 m Ah g^(-1) at 16 A g^(-1))and long cycling stability(a capacity retention of 78.6%after 800 cycles at 1 A g^(-1)).The present work highlights that the surface pseudocapacitive sodium-ion storage mechanism enables to overcome the sluggish sodium-ion diffusion process,which opens a new direction to design and synthesize high-rate sodiumion storage materials.

Improvement of doping efficiency in Mg-Al_(0.14)Ga_(0.86)N/GaN superlattices with AlN interlayer by suppressing donor-like defects

We investigate the mechanism for the improvement of p-type doping efficiency in Mg-Al0.14Ga0.86N/GaN super- lattices （SLs）. It is shown that the hole concentration of SLs increases by nearly an order of magnitude, from 1.1 × 1017 to 9.3×1017 cm-3, when an AlN interlayer is inserted to modulate the strains. SchrSdinger-Poisson self-consistent calculations suggest that such an increase could be attributed to the reduction of donor-like defects caused by the strain modulation induced by the AlN interlayer. Additionally, the donor-acceptor pair emission exhibits a remarkable decrease in intensity of the cathodoluminescence spectrumlfor SLs with an A1N interlayer. This supports the theoretical calculations and indicates that the strain modulation of SLs could be beneficial to the donor-like defect suppression as well as the p-type doping efficiency improvement.

Magnetic sensitivity technology based on microwave modulation of solid state spin system NV center

In view of the low resolution and accuracy of traditional magnetometer,a method of microwave frequency modulation technology based on nitrogen-vacancy(NV)center in diamond for magnetic detection was proposed.The magnetometer studied can reduce the frequency noise of system and improve the magnetic sensitivity by microwave frequency modulation.Firstly,ESR spectra by sweeping the microwave frequency was obtained.Further,the microwave frequency modulated was gained through the mixed high-frequency sinusoidal modulation signal generated by signal generator.In addition,the frequency through the lock-in amplifier was locked,and the signal which was proportional to the first derivative of the spectrum was obtained.The experimental results show that the sensitivity of magnetic field detection can reach 17.628 nT/Hz based on microwave frequency modulation technology.The method realizes high resolution and sensitivity for magnetic field detection.

^(15)N/^(14)N Isotopic Exchange in the Dissociative Adsorption of N_(2) on Tantalum Nitride Cluster Anions Ta_(3)N_(3)

Adsorption and activation of dinitrogen(N_(2)) is an indispensable process in nitrogen fixation.Metal nitride species continue to attract attention as a promsing catalyst for ammonia synthesis.However,the detailed mechanisms at a molecular level between reactive nitride species and N_(2) remain unclear at elevated temperature,which is important to understand the temperature effect and narrow the gap between the gas phase system and condensed phase system.Herein,the ^(15)N/^(14)N isotopic exchange in the reaction between tantalum nitride cluster anions Ta_(3)^(14)N_(3)^(-) and ^(15)N_(2) leading to the regeneration of ^(14)N_(2)/^(14)N^(15)N was observed at elevated temperature(393-593 K)using mass spectrometry.With the aid of theoretical calculations,the exchange mechanism and the effect of temperature to promote the dissociation of N_(2) on Ta_(3)N_(3)^(-) were elucidated.A comparison experiment for Ta_(3)^(14)N_(4)^(-)/^(15)N_(2) couple indicated that only desorption of ^(15)N_(2) from Ta_(3)^(14)N_(4)^(15)N_(2)^(-) took place at elevated temperature.The different exchange behavior can be well understood by the fact that nitrogen vacancy is a requisite for the dinitrogen activation over metal nitride species.This study may shed light on understanding the role of nitrogen vacancy in nitride species for ammonia synthesis and provide clues in designing effective catalysts for nitrogen fixation.

Synthesis of porous few-layer carbon nitride with excellent photocatalytic nitrogen fixation

The porous few-layer g-C_(3)N_(4)(PFL-g-C_(3)N_(4))is prepared by a simple molecular self-assembly method.Compared with pure g-C_(3)N_(4),the as-prepared PFL-g-C_(3)N_(4) is ultrathin,the surface is rich in pores,and the photocatalytic nitrogen fixation activity is greatly increased to 8.20 mM h^(-1) gCat^(-1).Few-layer and ultrathin nature of PFL-g-C_(3)N_(4) can provide a larger specific surface area,expose more active sites,and reduce the diffusion path of charges and protons from the inside to the surface.In addition,the porous structure can narrow the band gap,thereby increasing the light absorption range and enhancing the light absorption capability.Meanwhile,the presence of nitrogen vacancies causes PFL-g-C_(3)N_(4) to move to a more negative conductive band value.More importantly,the isotopic experiments using ^(15)N_(2) as nitrogen source confirm the ammonia production originating from N2 rather than the decomposition of g-C_(3)N_(4).Therefore,PFL-g-C_(3)N_(4) can greatly improve the efficiency of visible light photocatalytic nitrogen fixation.

Efficient photon coupling from a diamond nitrogen vacancy center by integration with silica fiber

A central goal in quantum information science is to efficiently interface photons with single optical modes for quantum networking and distributed quantum computing.Here,we introduce and experimentally demonstrate a compact and efficient method for the low-loss coupling of a solid-state qubit,the nitrogen vacancy(NV)center in diamond,with a single-mode optical fiber.In this approach,single-mode tapered diamond waveguides containing exactly one high quality NV memory are selected and integrated on tapered silica fibers.Numerical optimization of an adiabatic coupler indicates that near-unity-efficiency photon transfer is possible between the two modes.Experimentally,we find an overall collection efficiency between 16%and 37%and estimate a single photon count rate at saturation above 700 kHz.This integrated system enables robust,alignment-free,and efficient interfacing of single-mode optical fibers with single photon emitters and quantum memories in solids.

Influence of Nitrogen Vacancy Concentration on Mechanical and Electrical Properties of Rocksalt Zirconium Nitride Films

To study the influence of the nitrogen vacancy （VN） on mechanical and electrical properties of zirconium nitride deeply, ZrNx films with different VN concentrations were synthesized on the Si （111） substrates by enhanced magnetic filtering arc ion plating. The morphologies, microstructures, residual stresses, compositions, chemical states, mechanical and electrical properties of the as-deposited films were characterized by field-emission scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectrometry, Nanoindenter and Hall effect measurements. The results showed that ZrNx films exhibited rocksalt single-phase structure within a VN concentration ranging from 26 to 5%. The preferred orientation, thickness, grain size and residual stress of the ZrNx films kept constant at different VN concentrations. Both the nanohardness and elastic modulus first increased and then decreased with the decrease in VN concentration, reaching the peaks around 16%. And the electric conductivity of the ZrNx films showed a similar tendency with nanohardness. The underlying atomic-scale mechanisms of VN concentration-dependent hardness and electric conductivity enhancements were discussed and attributed to the different electronic band structures, rather than conventional meso-scale factors, such as preferred orientation, grain size and residual stress.

Quantum information processing and metrology with color centers in diamonds

The Nitrogen Vacancy （NV） center is becoming a promising qubit for quantum information processing. The defect has a long coherence time at room temperature and it allows spin state initialized and read out by laser and manipulated by microwave pulses. It has been utilized as a ultra sensi- tive probe for magnetic fields and remote spins as well. Here, we review the recent progresses in experimental demonstrations based on NV centers. We first introduce our work on implementation of the Deutsch- Jozsa algorithm with a single electronic spin in diamond. Then the quantum nature of the bath around the center spin is revealed and continuous wave dynamical decoupling has been demonstrated. By applying dynamical decoupling, a multi-pass quantum metrology protocol is realized to enhance phase estimation. In the final, we demonstrated NV center can be regarded as a ultra-sensitive sensor spin to implement nuclear magnetic resonance （NMR） imaging at nanoscale.

Drag-reduction of 3D printed shark-skin-like surfaces

The marvels of the slippery and clean sharkskin have inspired the development of many clinical and engineering products, although the mechanisms of interfacial interaction between the sharkskin and water have yet to be fully understood. In the present research, a methodology was developed to evaluate morphological parameters and to enable studying the effects of scale orientation on the fluidic behavior of water. The scale orientation of a shark skin was defined as the angle between the ridges and fluid flow direction. Textured surfaces with a series orientation of scales were designed and fabricated using 3 D printing of acrylonitrile butadiene styrene(ABS). The fluid drag performance was evaluated using a rheometer. Results showed that the shark–skin-like surface with 90 degree orientation of scales exhibited the lowest viscosity drag. Its maximum viscosity reduction was 9%. A viscosity map was constructed based on the principals of fluid dynamic. It revealed that the drag reduction effect of a shark-skin-like surface was attributed to the low velocity gradient. This was further proven using diamond nitrogen-vacancy sensing where florescent diamond particles were distributed evenly when the velocity gradient was at the lowest. This understanding could be used as guidance for future surface design.

Improving the NV generation efficiency by electron irradiation

The nitrogen vacancy(NV)center in diamond has been well applied in quantum sensing of electromagnetic field and temperature,where the sensitivity can be enhanced by the number of NV centers.Here,we used electron beam irradiation to increase the generation rate of NV centers by nearly 22 times.We systematically studied the optical and electronic properties of the NV center as a function of an electron irradiation dose,where the detection sensitivity of magnetic fields was improved.With such samples with dense NV centers,a sub-pico-Tesla sensitivity in magnetic fields detection can be achieved with optimal controls and detections.

Monolayer MoSi_(2)_N(4-x) as promising electrocatalyst for hydrogen evolution reaction: A DFT prediction

The density functional theory(DFT)calculations have been performed to investigate the catalytic properties of monolayer MoSi_(2)N_(4) for hydrogen evolution reaction(HER).The DFT results show that similar to the majority of other two-dimensional(2D)materials,the pristine MoSi_(2)N_(4) is inert for HER due to its weak affinity toward hydrogen,while monolayer MoSi_(2)N_(4-x)(x=0–0.25)exhibits the highly desirable HER catalytic activities by introducing surface nitrogen vacancy(NV).The predicted HER overpotential(0–60 mV)of monolayer MoSi_(2)N_(4-x) is lower than that(90 mV)of noble metal Pt,when the concentration of surface NV is lower than 5.6%.Electronic structure calculations show that the spin-polarized states appear around the Fermi level after introducing surface NV,thus making the surface NV on 2D MoSi_(2)N_(4) a quite suitable site for HER.Moreover,the HER activity of MoSi_(2)N_(4-x) is highly dependent on the surface NV concentration,which can be further related to the center of Si-3p band.Our results demonstrate that the newly discovered 2D MoSi_(2)N_(4) can be served as a promising electrocatalyst for HER via appropriate defect engineering.

New design concept for stableα-silicon nitride based on the initial oxidation evolution at the atomic and molecular levels

As the dominated composition of Si_(3)N_(4)ceramics,α-silicon nitride(α-Si_(3)N_(4))can satisfy the strength and fracture toughness demand in the applications.However,α-Si_(3)N_(4)is oxygen-sensitive at high temperatures,which limits its high-temperature performance.To improve the oxidation resistance ofα-Si_(3)N_(4)ceramics,it is necessary to shed light on the oxidation mechanism.Herein,the initial oxidation ofα-Si_(3)N_(4)was systematically studied at the atomic and molecular levels.The density functional theory(DFT)calculation denotes that the(001)surface ofα-Si_(3)N_(4)has the best stability at both room temperature and high temperature.Besides,the oxidation process of theα-Si_(3)N_(4)(001)surface consists of O adsorption and N desorption,and the consequent formation of nitrogen-vacancy(VN)is the key step for further oxidation.Moreover,the molecular dynamics(MD)simulation indicates that the oxidation rate ofα-Si_(3)N_(4)(100)surface is slower than that ofα-Si_(3)N_(4)(001)surface due to the lower N concentration at the outermost layer.Therefore,the oxidation resistance ofα-Si_(3)N_(4)can be improved by regulating the(100)surface as the dominant exposure surface.In addition,reducing the concentration of N on the final exposed surface ofα-Si_(3)N_(4)by mean of constructing the homojunction of the Si-terminal(100)surface and other N-containing surfaces(such as(001)surface)should be also a feasible approach.