Core-shell Nanowire Arrays Research Articles

Enhanced charge separation and transfer through Fe2O3/ITO nanowire arrays wrapped with reduced graphene oxide for water-splitting

This work reports the synthesis and investigation of reduced graphene oxide (rGO)-wrapped ITO@Fe2O3 (rGO-ITO@Fe2O3) core-shell nanowire arrays for water splitting, in which Fe2O3 nanorods are primary light-absorber, ITO nanowires act as high speed electron conductor and rGO as highly active electrocatalyst. This design considerably reduced the charge transfer and injection resistance, thus decreasing the recombination and improving the oxygen reaction kinetics. As a result, the rGO-ITO@Fe2O3 photoanode yields a photocurrent up to 5.38mAcm−2 at 0.6V (versus SCE), which is 3.5 times and 10 times of ITO@Fe2O3 and Fe2O3 in the same situation. The rGO-ITO@Fe2O3 photoanode also exhibits an excellent photoelectrochemical stability and there is no obvious degradation after 60min. Our work has provided an efficient strategy to improve the energy conversion efficiency and life-time of water splitting materials.

Self-catalyzed growth of Cu@graphdiyne core–shell nanowires array for high efficient hydrogen evolution cathode

Here we show that a high efficient hydrogen evolution reaction which was carried out on the in-situ growth of self-supported core-shell nanowires array consisting of graphdiyne as the shell and Cu as the core on Cu foams (Cu@GD NA/CF). Subject to potential cycling treatment in 0.5M H2SO4, the Cu@GD NA/CF exhibits highly catalytic activity for hydrogen evolution reaction with an onset overpotential of 52mV and a Tafel slope of 69mVdec−1. Our findings suggest that synergetic interaction between GD and Cu is crucial for the catalytic performance of the electrode. This electrode needs only overpotentials of 79 and 162mV to achieve catalytic current densities of 10 and 100mAcm–2, respectively, and maintains its catalytic activity for almost 20h. The attractive performances of such array make it promising candidate as a future high-performance catalyst for applications. SummaryThe first GD based 3D carbon nanoarchitectures with well-defined porous network structures working as a highly active hydrogen evolution cathode is developed. Its excellent electrocatalytic activities, combined with low-cost, convenient and scale-up preparation process, make it promising candidate for practical and efficient energy applications.

Cobalt Oxide@Tin Oxide@Silver Core–Shell Nanowire Arrays as Electrodes for Lithium‐Ion Batteries

AbstractThree‐dimensional Co3O4@SnO2@Ag core–shell nanowire arrays are prepared by the hydrothermal synthesis of Co3O4 nanowire arrays and subsequent deposition of SnO2 and Ag by radiofrequency sputtering. When used as anode materials in lithium‐ion batteries, the Co3O4@SnO2@Ag core–shell nanowire arrays show good cycling and rate performance, compared to corresponding Co3O4 arrays, Co3O4@SnO2 arrays, and Co3O4@SnO2@Ag planar electrodes. The enhanced performance can be attributed to the three‐dimensional core‐shell nanostructures and the addition of Ag, which can improves the electrical conductivity and structure stability during the charge/discharge process.

Cobalt Oxide–Tin Core–Shell Nanowire Arrays as High‐Performance Electrodes for Lithium‐Ion Batteries

AbstractBoth cobalt oxide and tin are electrochemically active materials, and can be integrated into hybrid core–shell nanowire structures that can participate in lithium‐ion insertion‐deinsertion process. We demonstrate the synthesis of cobalt oxide–tin (Co3O4–Sn) core–shell nanowire arrays by the hydrothermal synthesis of Co3O4 nanowire arrays and subsequent deposition of the tin layer via a RF‐sputtering method. When used as anode materials in lithium‐ion batteries, the Co3O4–Sn core–shell nanowire electrodes show better cyclability and enhanced rate capacities compared to bare Co3O4 electrodes. The improved performance can be attributed to the introduction of the tin layer, which improves the electrical conductivity and structural stability of the Co3O4 nanowire arrays.

Piezo-Phototronic Effect Enhanced Flexible Solar Cells Based on n-ZnO/p-SnS Core-Shell Nanowire Array.

The piezo‐phototronic effect is about the enhanced separation, transport, and recombination of the photogenerated carriers using the piezoelectric polarization charges present in piezoelectric‐semiconductor materials. Here, it is presented that the piezo‐phototronic effect can be effectively applied to improve the relative conversion efficiency of a flexible solar cell based on n‐ZnO/p‐SnS core–shell nanowire array for 37.3% under a moderate vertical pressure. The performance of the solar cell can be effectively enhanced by a gentle bending of the device, showing its potential for application in curly geometries. This study not only adds further understanding about the concept of increasing solar energy conversion efficiency via piezo‐phototronic effect, but also demonstrates the great potential of piezo‐phototronic effect in the application of large‐scale, flexible, and lightweight nanowire array solar cells.

Enhancing absorption in coated semiconductor nanowire/nanorod core–shell arrays using active host matrices

In the present work, we investigated theoretically and experimentally the interaction of radiation field phenomena interacting with arrays of nanowire/nanorod core–shell embedded in active host matrices. The optical properties of composites are explored including the case when the absorption of propagating wave by dissipative component is completely compensated by amplification in active (lasing) medium. On the basis of more elaborated modeling approach and extended effective medium theory, the effective polarizability and the refractive index of electromagnetic mode dispersion of the core–shell nanowire arrays are derived. ZnS(shell)-coated by sulphidation process on ZnO(shell) nanorod arrays grown on (100) silicon substrate by chemical bath deposition (CBD) has been used for theoretical comparison. Compared with the bare ZnO nanorods, ZnS-coated core/shell nanorods exhibit a strongly reduced ultraviolet (UV) emission and a dramatically enhanced deep level (DL) emission. Obviously, the UV and DL emission peaks are attributed to the emissions of ZnO nanorods within ZnO/ZnS core/shell nanorods. The reduction of UV emission after ZnS coating seems to agree with the charge separation mechanism of type-II band alignment that holes transfer from the core to shell, which would quench the UV emission to a certain extent. Our theoretical calculations and numerical simulation demonstrate that the use of active host (amplifying) medium to compensate absorption at metallic inclusions. Moreover the core–shell nanorod/nanowire arrays create the opportunity for broad band absorption and light harvesting applications.

The formation and characteristics of ZnO/AlN and ZnO/AlN/ZnO core-shell nanowires

ABSTRACTIn this work, we fabricate the p-type ZnO/AlN/ZnO core-shell nanowire arrays on Al2O3 substrate. The SEM images show the core-shell structure and the connection phenomenon appeared during the deposition process. The XRD results show a better crystal quality after annealing. The sample exhibits some unique properties after annealing treatment. Including the improvement of crystal quality and the shift of the PL emission peak. The low temperture PL spectra show a neutral acceptor bound exciton (A0X) emission (at 3.355 eV), and the emission at 3.325 eV is ascribe to the free electron to the acceptor transition (FA). The calculated result is found in good coincidence with the experiment.

Construction of CuO/Cu2O@CoO core shell nanowire arrays for high-performance supercapacitors

Abstract In this paper, we reported construction of CuO/Cu 2 O@CoO core-shell nanowire arrays by combining a chemical deposition method and post-thermal annealing process on Cu foil without any binders and conductive additives. The nanowire arrays were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM) and energy dispersive X-ray spectroscopy (EDX) techniques. The determination results indicate that the nanowire arrays are distinct CuO/Cu 2 O nanowire core decorated with branched CoO nanosheet shells. In addition, the as-obtained nanowire arrays demonstrate outstanding areal capacitance of 280 mF cm − 2 at a current density of 1 mA cm − 2 as well as superior cycling stability which remains 90.7% of initial capacitance after 3000 cycles. The facile and cost-effective synthesis integrated with the robust electrochemical performances suggests that the CuO/Cu 2 O@CoO core-shell nanowire arrays are expected to be promising candidate electrodes for high-performance supercapacitor and other energy storage applications.

Excellent Electrochemical Performance Hierarchical Co3O4@Ni3S2 core/shell nanowire arrays for Asymmetric Supercapacitors

Three-dimensional hierarchical Co3O4@Ni3S2 core/shell nanowire arrays were designed and fabricated on nickel foam via a facile two-step route for supercapacitor applications. Compared with the pristine Co3O4 nanowire arrays and Ni3S2 nanosheets, the hierarchical nanostructure demonstrates much more excellent capacitive behaviors. The Co3O4@Ni3S2 electrode exhibited an ultrahigh specific capacitance of 1710Fg−1 at 1Ag−1 and 1474Fg−1 at 10Ag−1. An asymmetric supercapacitor based on Co3O4@Ni3S2 core/shell nanowire arrays on nickel foam as the positive electrode and activated carbon (AC) as negative electrode was successfully assembled. A specific capacitance of 126.6Fg−1 at 1Ag−1 (retaining 83.5% capacity after 5000 cycles at a current density of 2Ag−1) and an outstanding energy density of 44.9 Wh kg−1 was achieved. The remarkable electrochemical properties could be attributed to the unique hierarchical architectures of Co3O4@Ni3S2 core–shell nanowire arrays on 3D on nickel foam and a rational combination of two electrochemical pseudocapacitor materials. The results indicate that our asymmetric supercapacitors have great potential in energy storage device applications.

Ti@δ-MnO2 core-shell nanowire arrays as self-supported electrodes of supercapacitors and Li ion batteries

δ-MnO2 is a promissing electrode material of supercapacitors and Li ion batteries (LIBs) owing to its low cost, layer structure and composite valence of Mn. However, the unfavorable electronic conductivity of δ-MnO2 restricts its rate capability in both of the two devices. Herein, a vertically standing Ti nanowire array modified with δ-MnO2 nanoflakes is prepared by a electrodeposition method, and the electrochemical properties of Ti@δ-MnO2 nanowire arrays in supercapacitors and LIBs are investigated. The results show that, the arrays have a capacity of 195Fg−1 at 1.0Ag−1 and can cycle more than 10000 rounds at 10Ag−1 as electrodes of supercapacitors. On the other hand, the arrays behave good rate capability as LIB cathodes, which can release a capacity of 70mAhg−1 at 10C rate charge/discharge. We suggest that, the good electronic conductivity owing to the core-shell structure and the facilitated mass transport supplied by the array architecture are responsible for the enhanced rate performances in the two devices.

Hierarchically MnO2-Nanosheet Covered Submicrometer-FeCo2O4-Tube Forest as Binder-Free Electrodes for High Energy Density All-Solid-State Supercapacitors.

The current problem of the still relatively low energy densities of supercapacitors can be effectively addressed by designing electrodes hierarchically on micro- and nanoscale. Herein, we report the synthesis of hierarchically porous, nanosheet covered submicrometer tube forests on Ni foam. Chemical deposition and thermal treatment result in homogeneous forests of 750 nm diameter FeCo2O4 tubes, which after hydrothermal reaction in KMnO4 are wrapped in MnO2-nanosheet-built porous covers. The covers' thickness can be adjusted from 200 to 800 nm by KMnO4 concentration. An optimal thickness (380 nm) with a MnO2 content of 42 wt % doubles the specific capacitance (3.30 F cm(-2) at 1.0 mA cm(-2)) of the bare FeCo2O4-tube forests. A symmetric solid-state supercapacitor made from these binder-free electrodes achieves 2.52 F cm(-2) at 2 mA cm(-2), much higher than reported for capacitors based on similar core-shell nanowire arrays. The large capacitance and high cell voltage of 1.7 V allow high energy and power densities (93.6 Wh kg(-1), 10.1 kW kg(-1)). The device also exhibits superior rate capability (71% capacitance at 20 mA cm(-2)) and remarkable cycling stability with 94% capacitance retention being stable after 1500 cycles.

Electrochemical Energy Storage Application and Degradation Analysis of Carbon-Coated Hierarchical NiCo2S4 Core-Shell Nanowire Arrays Grown Directly on Graphene/Nickel Foam.

We developed a new electrode comprising thin carbon layer coated hierarchical NiCo2S4 core-shell nanowire arrays (NiCo2S4@C CSNAs) on graphene/Ni foam (Ni@G) substrates. The electrode showed outstanding electrochemical characteristics including a high specific capacitance of 253 mAh g−1 at 3 A g−1, high rate capability of 163 mAh g−1 at 50 A g−1 (~64.4% of that at 3 A g−1), and long-term cycling stability with a capacity retention of 93.9% after 5000 cycles. Comparative studies on the degradation of hierarchical NiCo2S4 CSNA electrodes with and without carbon coatings revealed that the morphology pulverization, structural separation at core/shell interface, and irretrievably chemical composition change of NiCo2S4 CSNAs electrode are major factors that deteriorate the electrochemical performance of the electrodes without carbon coating. The favorable roles of carbon coatings on hierarchical NiCo2S4 CSNAs were further clarified: (1) serving as a physical buffering layer that suppresses the structural breakdown; (2) retarding the chemical composition conversion of the NiCo2S4 CSNAs; and (3) providing extra path for charge transition in addition to the NiCo2S4 core nanowires. Understanding of the degradation mechanisms and the significance of the surface carbon coatings would provide useful guidelines for the design of new electrode materials for high-performance electrochemical devices.

Hierarchical structures composed of MnCo2O4@MnO2 core-shell nanowire arrays with enhanced supercapacitor properties.

In this paper, hierarchical MnCo2O4@MnO2 core-shell nanowire arrays (MnCo2O4@MnO2 NWAs) with mesoporous and large surface area are synthesized on 3D nickel foam via a facile, two-step hydrothermal approach without any adscititious surfactant and binder. The electrode architecture takes advantage of the synergistic effects contributed from both the porous MnCo2O4 nanowire core and the MnO2 shell layer. The fabricated MnCo2O4@MnO2 NWA electrode for supercapacitors in aqueous electrolyte exhibits a significantly enhanced specific capacitance (858 F g(-1) at 1 A g(-1)), high energy density (36.0 Wh kg(-1) at 252 W kg(-1)) and long-life cycling stability (retaining 88% of the initial capacitance after 5000 cycles). Then, a symmetrical supercapacitor is fabricated by assembling two MnCo2O4@MnO2 NWA-based electrodes, which shows a high specific capacitance of 678 F g(-1) at 1 A g(-1) and a high energy density of 135.6 Wh kg(-1) at 513 W kg(-1). Thereby, the hierarchical core-shell MnCo2O4@MnO2 NWAs are very promising as next generation high-performance long-life cycling supercapacitors.

A novel Co–Li2O@Si core–shell nanowire array composite as a high-performance lithium-ion battery anode material

We report a novel material of Co-Li2O@Si core-shell nanowire array synthesized via the lithiation of pre-synthesized CoO@Si core-shell nanowire arrays during the first cycle. When the potential window versus lithium was controlled between 0.01-1.2 V, the coated Si shell could be electrochemically active, while the Co-Li2O nanowire core could function as a stable mechanical support and an efficient electron conducting pathway during the charge-discharge process. The Co-Li2O@Si core-shell nanowire array anodes exhibit good cyclic stability and high power capability compared to planar Si film electrodes.

3D hierarchical CuO/Co3O4 core–shell nanowire array on copper foam for on-demand hydrogen generation from alkaline NaBH4 solution

A 3D hierarchical CuO/Co3O4 core–shell nanowire array works as a robust and highly active catalyst toward the hydrolytic dehydrogenation of NaBH4 for on-demand hydrogen generation in alkaline solutions.

Binder-free Co3O4@NiCoAl-layered double hydroxide core-shell hybrid architectural nanowire arrays with enhanced electrochemical performance

Herein, binder-free Co3O4@NiCoAl-layered double hydroxide (Co3O4@LDH) core-shell hybrid architectural nanowire arrays were prepared via a two-step hydrothermal synthesis route. LDH nanosheets possessing a large electroactive surface area uniformly dispersed on the surface of Co3O4 nanowires were successfully fabricated allowing for fast electron transport that enhances the electrochemical performance of LDH nanosheets. Co3O4@LDH nanowire arrays of 2 to 1.5 molar ratio (Co3O4:LDH) exhibit high specific capacitance (1104Fg−1 at 1Ag−1), adequate rate capability and cycling stability (87.3% after 5000 cycles), attributed to the synergistic effect between the robust Co3O4 nanowire arrays and LDH nanosheets.

Enhanced Performance of Photoelectrochemical Water Splitting with ITO@α-Fe2O3 Core-Shell Nanowire Array as Photoanode.

Hematite (α-Fe2O3) is one of the most promising candidates for photoelectrodes in photoelectrochemical water splitting system. However, the low visible light absorption coefficient and short hole diffusion length of pure α-Fe2O3 limits the performance of α-Fe2O3 photoelectrodes in water splitting. Herein, to overcome these drawbacks, single-crystalline tin-doped indium oxide (ITO) nanowire core and α-Fe2O3 nanocrystal shell (ITO@α-Fe2O3) electrodes were fabricated by covering the chemical vapor deposited ITO nanowire array with compact thin α-Fe2O3 nanocrystal film using chemical bath deposition (CBD) method. The J-V curves and IPCE of ITO@α-Fe2O3 core-shell nanowire array electrode showed nearly twice as high performance as those of the α-Fe2O3 on planar Pt-coated silicon wafers (Pt/Si) and on planar ITO substrates, which was considered to be attributed to more efficient hole collection and more loading of α-Fe2O3 nanocrystals in the core-shell structure than planar structure. Electrochemical impedance spectra (EIS) characterization demonstrated a low interface resistance between α-Fe2O3 and ITO nanowire arrays, which benefits from the well contact between the core and shell. The stability test indicated that the prepared ITO@α-Fe2O3 core-shell nanowire array electrode was stable under AM1.5 illumination during the test period of 40,000 s.

Photonic band structure and effective medium properties of doubly-resonant core-shell metallo-dielectric nanowire arrays: low-loss, isotropic optical negative-index behavior

We investigate theoretically and numerically the photonic band structure in the optical domain of an array of core–shell metal-semiconductor nanowires. Corresponding negative-index photonic bands are calculated, showing isotropic equifrequency surfaces. The effective (negative) electric permittivity and magnetic permeability, retrieved from S-parameters, are used to compare the performance of such nanowire arrays with homogeneous media in canonical examples, such as refraction through a prism and flat-lens focusing. Very good agreement is found, confirming the effective medium behavior of the nanowire array as a low-loss, isotropic (2D) and bulk, optical negative index metamaterial. Indeed, disorder is introduced to further stress its robustness.

Coaxial three-dimensional CoMoO4 nanowire arrays with conductive coating on carbon cloth for high-performance lithium ion battery anode

Nanostructured transition metal oxides have attracted considerable attentions for both high-capacity and high-rate, but great challenges remain to utilize them. In order to overcome these challenges, hierarchical three-dimensional CoMoO4/polypyrrole core-shell nanowire (NW) arrays on flexible and conductive carbon cloth (CC) have been successfully constructed through a facile two-step solution-based approach. The hybrid NWs electrode as a binder-free lithium ion batteries (LIBs) anode material exhibits a reversible capacity of around 1400–1450 mAh g−1 at a low current density of 100 mA g−1. The specific capacity retains at 753 mAh g−1 while featuring an excellent cycling properties with a capacity of 764 mAh g−1 after 1000 cycles under the current rate of 1200 mA g−1. Furthermore, full batteries have been fabricated and demonstrated characteristics of outstanding electrical stability and superior power output characteristics, which represents an efficient way for practical implementation.

3D TiO2@Ni(OH)2 Core-shell Arrays with Tunable Nanostructure for Hybrid Supercapacitor Application.

Three dimensional hierarchical nanostructures have attracted great attention for electrochemical energy storage applications. In this work, self-supported TiO2@Ni(OH)2 core-shell nanowire arrays are prepared on carbon fiber paper via the combination of hydrothermal synthesis and chemical bath deposition. In this core-shell hybrid, the morphology and wall size of the interconnected nanoflake shell of Ni(OH)2 can be tuned through adjusting the concentration of ammonia solution. Heterogeneous nucleation and subsequent oriented crystal growth are identified to be the synthesis mechanism affecting the nanostructure of the shell material, which consequently determines the electrochemical performance in both energy storage and charge transfer. Superior capabilities of 264 mAhg−1 at 1 A g−1 and 178 mAh g−1 at 10 A g−1 are achieved with the core-shell hybrids of the optimized structure. The asymmetric supercapacitor prototype, comprising of TiO2@Ni(OH)2 as the anode and mesoporous carbons (MCs) as the cathode, is shown to exhibit superior electrochemical performance with high energy and power densities. The present work provides a clear illustration of the structure-property relationship in nanocrystal synthesis and offers a potential strategy to enhance the battery type Ni(OH)2 electrode in a hybrid supercapacitor device.