A core-shell copper oxides-cobalt oxides heterostructure nanowire arrays for nitrate reduction to ammonia with high yield rate

Electrochemical nitrate reduction to ammonia(NRA) can realize the green synthesis of ammonia(NH3) at ambient conditions, and also remove nitrate contamination in water. However, the current catalysts for NRA still face relatively low NH3yield rate and poor stability. We present here a core-shell heterostructure comprising cobalt oxide anchored on copper oxide nanowire arrays(CuO NWAs@Co_(3)O_(4)) for efficient NRA. The CuO NWAs@Co_(3)O_(4)demonstrates significantly enhanced NRA performance in alkaline media in comparison with plain CuO NWAs and Co_(3)O_(4)flocs. Especially, at-0.23 V vs. RHE, NH_(3) yield rate of the CuO NWAs@Co_(3)O_(4)reaches 1.915 mmol h^(-1)cm^(-2),much higher than those of CuO NWAs(1.472 mmol h^(-1)cm^(-2)), Co_(3)O_(4)flocs(1.222 mmol h^(-1)cm^(-2)) and recent reported Cu-based catalysts.It is proposed that the synergetic effects of the heterostructure combing atom hydrogen adsorption and nitrate reduction lead to the enhanced NRA performance.

Nickel and indium core-shell co-catalysts loaded silicon nanowire arrays for efficient photoelectrocatalytic reduction of CO_(2) to formate

Developing an efficient artificial photosynthetic system for transforming carbon dioxide and storing solar energy in the form of chemical bonds is one of the greatest challenges in modern chemistry.However,the limited choice of catalysts with wide light absorption range,long-term stability and excellent selectivity for CO_(2) reduction makes the process sluggish.Here,a core-shell-structured nonnoble-metal Ni@In co-catalyst loaded p-type silicon nanowire arrays(SiNWs)for efficient CO_(2) reduction to formate is demonstrated.The formation rate and Faradaic efficiency of formate over the Ni@In/SiNWs catalyst reach 58μmol h^(-1) cm^(-2) and 87% under the irradiation of one simulated sunlight(AM 1.5 G,100 mW cm^(-2)),respectively,which are about 24 and 12 times those over the pristine SiNWs.The enhanced photoelectrocatalytic performance for CO_(2) reduction is attributed to the rational combination of Ni capable of effectively extracting the photogenerated electrons and In responsible for the selective activation of CO_(2).

Hierarchical Self-assembly of Well-Defined Louver-Like P-Doped Carbon Nitride Nanowire Arrays with Highly Effcient Hydrogen Evolution

Self-assembled nanostructure arrays integrating the advantages of the intrinsic characters of nanostructure as well as the array stability are appealing in advanced materials.However,the precise bottom-up synthesis of nanostructure arrays without templates or substrates is quite challenging because of the general occurrence of homogeneous nucleation and the difficult manipulation of noncovalent interactions.Herein,we first report the precisely manipulated synthesis of well-defined louver-like P-doped carbon nitride nanowire arrays(L-PCN)via a supramolecular self-assembly method by regulating the noncovalent interactions through hydrogen bond.With this strategy,CN nanowires align in the outer frame with the separation and spatial location achieving ultrastability and outstanding photoelectricity properties.Significantly,this self-assembly L-PCN exhibits a superior visible light-driven hydrogen evolution activity of 1872.9μmol h^−1 g^−1,rendering a^25.6-fold enhancement compared to bulk CN,and high photostability.Moreover,an apparent quantum efficiency of 6.93%is achieved for hydrogen evolution at 420±15 nm.The experimental results and first-principles calculations demonstrate that the remarkable enhancement of photocatalytic activity of L-PCN can be attributed to the synergetic effect of structural topology and dopant.These findings suggest that we are able to design particular hierarchical nanostructures with desirable performance using hydrogen-bond engineering.

Preparation and characterization of highly ordered NiO nanowire arrays by sol-gel template method

Highly ordered nickel monoxide （NiO） nanowire arrays were fabricated by sol-gel synthesis within the pores of anodic alumina membrane （AAM）. Scanning electron microscopy （SEM）, high resolution transmission electron microscopy （HRTEM） and X-ray diffraction （XRD） were used to characterize the topography and crystalloid structure of NiO nanowire arrays. The length and diameter of the NiO nanowires depended on the thickness of the AAM and the diameter of the pores. The results indicated that the NiO nanowires were uniformly assembled into the ordered nanopores of the AAM and paralleled to each other. Nickel monoxide nanotubes were also fabricated with the same method by changing the immersing time. This new method to prepare NiO nanowire arrays may be important from gas sensors to various engineering materials.

Superior surface electron energy level endows WP_(2) nanowire arrays with N_(2) fixation functions

Nitrogen reduction reaction(NRR)under ambient conditions is always a long-standing challenge in science,due to the extreme difficulty in breaking the strong N≡N triple bond.The key to resolving this issue undoubtedly lies in searching superior catalysts to efficiently activate and hydrogenate the stable nitrogen molecules.We herein evaluate the feasibility of WP_(2) for N2 activation and reduction,and first demonstrate WP_(2) with an impressive ammonia yield rate of 7.13 lg h^(-1)cm^(-2),representing a promising W-based catalyst for NRR.DFT analysis further reveals that the NRR catalysis on WP_(2) proceeds in a distal reaction pathway,and the exceptional NRR activity is originated from superior surface electron energy level matching between WP_(2) and NRR potential which facilitates the interfacial proton-coupled electron transfer dynamics.The successfully unraveling the intrinsic catalytic mechanism of WP_(2) for NRR could offer a powerful platform to manipulate the NRR activity by tuning the electron energy levels.

Seed Free Growth of Aligned ZnO Nanowire Arrays on AZO Substrate

In the absence of commonly used seed layer, we can still successfully synthesized aligned ZnO nanowire arrays by the hydrothermal method. By using aluminum-doped zinc oxide(AZO) glass as a substrate, high-density and vertically aligned ZnO nanowires were synthesized directly on the substrate in the absence of the ZnO seed layer. The current-voltage curve indicated that the sample grown on AZO glass substrate in the absence of seed layer possesses better conductivity than that synthesized on FTO glass substrate with ZnO seed layer. Thus, a simplified, seed-free and low-cost experimental protocol was reported here for large-scale production of high quality ZnO nanowire arrays with promoted conductivity.

Ag-modified hydrogen titanate nanowire arrays for stable lithium metal anode in a carbonate-based electrolyte

In the investigation of the next-generation battery anode,Li metal has attracted increasing attention owing to its ultrahigh specific capacity and low reduction potential.However,its low columbic efficiency,limited cycling life,and serious safety hazards have hindered the practical application of rechargeable Li metal batteries.Although several strategies have been proposed to enhance the electrochemical performance of Li metal anodes,most are centered around ether-based electrolytes,which are volatile and do not provide a sufficiently large voltage window.Therefore,we aimed to attain stable Li deposition/stripping in a commercial carbonate-based electrolyte.Herein,we have successfully synthesized hydrogen titanate(HTO)nanowire arrays decorated with homogenous Ag nanoparticles(NPs)(Ag@HTO)via simple hydrothermal and silver mirror reactions.The 3 D cross-linked array structure with Ag NPs provides preferable nucleation sites for uniform Li deposition,and most importantly,when assembled with the commercial LiNi_(0.5)Co0.2Mn_(0.3)O_(2) cathode material,the Ag@HTO could maintain a capacity retention ratio of 81.2% at 1 C after 200 cycles,however the pristine Ti foil failed to do so after only 60 cycles.Our research therefore reveals a new way of designing current collectors paired with commercial high voltage cathodes that can create high energy density Li metal batteries.

Growth of high-crystallinity uniform GaAs nanowire arrays by molecular beam epitaxy

The self-catalyzed growth of Ga As nanowires(NWs)on silicon(Si)is an effective way to achieve integration between group III–V elements and Si.High-crystallinity uniform Ga As NW arrays were grown by solid-source molecular beam epitaxy(MBE).In this paper,we describe systematic experiments which indicate that the substrate treatment is crucial to the highly crystalline and uniform growth of one-dimensional nanomaterials.The influence of natural oxidation time on the crystallinity and uniformity of Ga As NW arrays was investigated and is discussed in detail.The Ga As NW crystallinity and uniformity are maximized after 20 days of natural oxidation time.This work provides a new solution for producing high-crystallinity uniform III–V nanowire arrays on wafer-scale Si substrates.The highly crystalline uniform NW arrays are expected to be useful for NW-based optical interconnects and Si platform optoelectronic devices.

Study of Shifted UV Emission Peak of ZnO Nanowire Arrays

We have obtained vertically aligned ZnO nanowire arrays synthesized by microwave-assisted heating method with different growth time.From the room-temperature PL measurement,the strong deep-level emission and weak near band edge(NBE)emission can be seen.The deep-level emissions became weaker and deep-level emissions became stronger when the samples were annealed at 300℃for 30 min,meanwhile,the NBE emission peaks get red-shifted with growth time,and the longer the growth time,the more the peak shifting.This phenomenon can be attributed that the diameter of ZnO nanowires increases with growth time.This PL emission phenomenon is important in research of optoelectronic application.

Mechanically tunable broadband terahertz modulator based on high-aligned Ni nanowire arrays

We present a mechanically tunable broadband terahertz(THz) modulator based on the high-aligned Ni nanowire(NW)arrays. The modulator is a sandwich structure consisting of two polydimethylsiloxane layers and a central layer of highaligned Ni NW arrays. Our experimental measurements reveal the transmittance of THz wave can be effectively modulated by mechanical stretching. The NW density in arrays increases with the strain increasing, which induced an enhancement in the absorption of THz wave. When the strain increases from 0 to 6.5%, a linear relationship is observed for the variation of modulation depth(MD) of THz wave regarding the strain, and the modulated range is from 0 to 85% in a frequency range from 0.3 THz to 1.8 THz. Moreover, the detectable MD is about 15% regarding the 1% strain change resolution. This flexible Ni NW-based modulator can be promised many applications, such as remote strain sensing, and wearable devices.

Effect of Polyethyleneimine Assisting the Growth of Eu-doped ZnO Nanowire Arrays in Mannich Reaction

In study on the growth reaction mechanism of Eu-doped ZnO nanowire（NW）, the intermedium of reaction is characterized by measures such as FTIR. Besides, the influences of polyethyleneimine（PEI） on morphology, structure and photoelectric property of NW are observed by SEM, TEM, XRD, UV-vis and PL spectrum. According to the result, it manifests that Eu-doped ZnO NW array growth response experiences six mutually associated reaction processes in PEI-HMTA system：（a） chelation reaction of PEI and Zn^2＋ ＆ Eu^3＋;（b） protonation reaction of PEI and NH_3;（c） decomposition reaction of hexamethylenetetramine（HMTA）;（d） Mannich reaction of HCHO and PEI;（e） formation of precursor of Eu-doped ZnO;（f） dehydration condensation of Eu-doped ZnO precursors, further forming a doped ZnO NW array. Among them, PEI is the key factor of the whole doping growth reaction process. It both plays a role in modifying the growth of ZnO NW and makes it become longer and thinner. In the meantime, it also facilitates doping of Eu and enables ZnO NW to capture more photoelectrons and higher transmission rate, which is critical to improve photovoltaic performance of optoelectronic devices.

Researchers in Xi'an Jiaotong University have made important progress in the research of flexible epitaxial magnetic nanowire arrays

In recent years,flexible materials are widely concerned by scientists because of their unique bendingproperties and potential applications in flexible wearable electronic devices.Magnetic material,especially one dimensional nano structure with high orientation,are also research focus for researchers due to their important applications in the fields of high density magnetic storage and sensors.Compared

Integration of urchin-like MnCo_(2)O_(4)@C core–shell nanowire arrays within porous copper current collector for superior performance Li-ion battery anodes

Spinel MnCo_(2)O_(4) is a promising energy storage candidate as anode materials in lithium-ion batteries owing to synergistic effects of two intrinsic solid-state redox couples.However,low conductivity,poor rate capacity and rapid capacity fading have seriously impaired its practical applications.To overcome the inferiorities,urchin-like MnCo_(2)O_(4)@C core–shell nanowire arrays have been fabricated directly within a porous copper current collector via a facile hydrothermal method followed by a chemical vapor deposition carbonization process.In a typical nanowire,the core is composed of interconnected MnCo_(2)O_(4)nanoparticles and the shell shows as a thin amorphous carbon layer.The integrated MnCo_(2)O_(4)@C/Cu structure could act as working anodes without using additives or polymer binders.While MnCo_(2)O_(4)@C/Cu possesses slightly longer Li-ion insertion/desertion pathway than that of MnCo_(2)O_(4)/Cu,the carbon shell could effectively prevent the pulverization of MnCo_(2)O_(4) and lower down charge transfer resistance and actively participate in Li-ion cycles.The rearrangement of carbon atoms during lithiation/delithiation cycling could inhibit the formation of passive solid electrolyte interphase films.As a result,the MnCo_(2)O_(4)@C/Cu electrode presents superior rate capacity(600 mAh·g^(−1) at 1 A·g^(−1)) and better stability(797 mAh·g^(−1) after 200 cycles at 100 mA·g^(−1)).The excellent reversible Li ion storage capacity,cycling stability and rate capacity endow MnCo_(2)O_(4)@C/Cu great potential as stable and high output integrated anode materials in Li-ion batteries.

Enhanced Photocatalytic Degradation of Rhodamine B by Cu_2O Coated Silicon Nanowire Arrays in Presence of H_2O_2

Highly ordered Cu2O coated silicon nanowire arrays （SiNWAs） were fabricated as photocatalyst via depositing Cu nanoparticles on silver-assisted electroless-etched SiNWAs and subsequently annealing. The as-prepared samples have been characterized by scanning electron microscopy, X-ray diffraction and UV-VIS-NIR spectrophotometry. The photocatalytic properties of the Cu2O coated SiNWAs were investigated by degradation of Rhodamine B （RhB） under simulated solar light with a cut-off filter （λ 〉 420 nm）. The results indicated that H2O2 could greatly improve the photocatalytic properties of Cu2O coated SiNWAs, and exhibited strong synergy effect between them. The hybrid nanowire arrays will be promising photocatalytic materials in the field of energy and environment.

Cu_(2)Sb decorated Cu nanowire arrays for selective electrocatalytic CO_(2)to CO conversion

The advancement of cost-effective and selective electrocatalyst towards CO_(2) to CO conversion is crucial for renewable energy conversion and storage,thus to achieve carbon-neutral cycle in a sustainable manner.In this communication,we report that CujSb decorated Cu nanowire arrays on Cu foil act as a highly active and selective electrocatalyst for CO_(2) to CO conversion.In CO_(2)-saturated 0.1 M KHCO_(3),it achieves a high Faraday efficiency(FE)of 86.5%for CO,at-0.90 V vs.reversible hydrogen electrode(RHE).The H_(2)/CO ratio is tunable from 0.08:1 to 5.9:1 by adjusting the potential.It is worth noting that HCOO-product was totally suppressed on such catalyst,compared with Sb counterpart.The improving selectivity for CO could be attributed to the bimetallic effect and nanowire arrays structure.

Hierarchical ferric-cobalt-nickel ternary oxide nanowire arrays supported on graphene fibers as high-performance electrodes for flexible asymmetric supercapacitors

Fiber-based supercapacitors （FSCs） are new members of the energy storage family. They present excellent flexibility and have promising applications in lightweight, flexible, and wearable devices. One of the existing challenges of FSCs is enhancing their energy density while retaining the flexibility. We developed a facile and cost-effective method to fabricate a highly capacitive positive electrode based on hierarchical ferric-cobalt-nickel ternary oxide nanowire arrays/graphene fibers and a negative electrode based on polyaniline-derived carbon nanorods/graphene fibers. The elegant microstructures and excellent electrochemical performances of both electrodes enabled us to construct a high- performance flexible asymmetric graphene fiber-based supercapacitor device with an operating voltage of 1.4 V, a specific capacitance up to 61.58 mF.cm-2, and an energy density reaching 16.76 μW·h·cm-2. Moreover, the optimal device presents an outstanding cycling stability with 87.5% initial capacitance retention after 8,000 cycles, and an excellent flexibility with a capacitance retention of 90.9% after 4,000 cycles of repetitive bending.

Growth modulation of simultaneous epitaxy of ZnO obliquely aligned nanowire arrays and film on r-plane sapphire substrate

Simultaneous epitaxial growth of film and nanowire array on a substrate is of both scientific significance and practical importance for nanoscale optoelectronics. Nevertheless, in situ building conducting connection between individually isolated nanowires grown on insulating substrates is still challenging. Herein, we demonstrate a novel and facile strategy for the simultaneous epitaxial growth of nonpolar a-plane ZnO film and obliquely aligned nanowire array on Au-coated r-plane sapphire substrate. The morphology, structure, components, and optical properties of the as-synthesized ZnO nanostructures were investigated using field-emission scanning electron microscopy X-ray diffraction, field-emission transmission electron microscopy energy-dispersive spectroscopy, X-ray photo- electron spectroscopy, and photoluminescence spectroscopy. A cooperative growth mechanism is proposed： Au-catalyzed vapor transport initiates the co-occurrence of nonpolar a-plane and polar c-plane ZnO nuclei, and subsequently, the non-upward directed Au catalyst helps the nonpolar a-plane ZnO nuclei develop into a ZnO conductive film at the bottom and zinc self-catalyzed vapor-liquid-solid growth helps the polar c-plane ZnO nuclei develop simultaneously into obliquely aligned nanowire arrays. The proposed strategy realized in situ synthesis of nanowires with conductive connection and it can benefit the application of ZnO nanowires in optoelectronics.

CeO2@NiCo2O4 nanowire arrays on carbon textiles as high performance cathode for Li-O2 batteries

The successful development of Li-O_2 battery technology depends on developing a stable and efficient cathode. As an important step toward this goal, for the first time, we report the development of CeO_2 nanoparticles modified NiCo_2O_4 nanowire arrays(NWAs) grown on the carbon textiles as a new carbon-free and binder-free cathode system. In this study, the Li-O_2 battery with the CeO_2@NiCo_2O_4 NWAs has exhibited much reduced overpotentials, a high discharge capacity, an improved cycling stability,outperforming the Li-O_2 battery with NiCo_2O_4 NWAs. These improvements can be attributed to both the tailored morphology of discharge product and improved oxygen reduction reaction(ORR) and oxygen evolution reaction(OER) activity after CeO_2 NPs deposition. To a considerable extent, this idea of cathode construction including structure design and composition optimization can provide guidance for further researches in developing more powerful cathode for Li-O_2 battery.

High-efficient electron collection capability of graded Al compositional GaN nanowire arrays cathode

Based on the purpose of solving the"secondary absorption"of adjacent nanowires and the lateral emission in the Ga N nanowire arrays(NWAs)cathode,an exponential-doping and graded Al compositional Ga N NWAs photocathode is proposed,which could generate internal electric field to increase the quantum efficiency(QE)of top surface,and the introduction of an external electric field promote the side-emission electrons to shift toward the collecting side.The QE and collection efficiency(CE)of exponential-doping and graded compositional Ga N NWAs under different array structure parameters,incident angles and external electric field intensities are analyzed.The results show that although the collection ratio of emitted electrons in the exponential-doping Ga N NWAs is higher,the graded Al compositional photocathode with a stronger built-in electric field can obtain better CE under the application of an external electric field,and the peak value can reach 33.2%in a specific structure.External electric field has a more significant effect on the CE of uniform-doping Ga N NWAs.The solutions provided in this study can make the Ga N NWAs photocathode more suitable for the strict requirements of vacuum electron sources.

Fabrication of Two Types of Ordered InP Nanowire Arrays on a Single Anodic Aluminum Oxide Template and Its Application in Solar Cells

Two types of ordered InP nanowire arrays have been prepared on the same anodic aluminum oxide template by a template-assisted metallo-organic chemical vapor deposition technique.When using template with an appropriate pore size,free-standing wires on the template surface and highly ordered wires in the nanochannels of the same template can be simultaneously achieved.The highly ordered InP nanowire arrays in the nanochannels serve as an n-type semiconductor to assemble the p-n heterojunction solar cell with p-type Cu2O.Such a Cu2O/lnP p-n heterojunction solar cell possesses a power conversion efficiency of 1.55%.