Core-shell Nanotube Arrays Research Articles

Facile Synthesis of 3D Cu(OH)2@NiCo-Binary Hydroxide Core–Shell Nanotube Arrays with High Mass Loading for High-Performance Asymmetric Supercapacitors

Facile Synthesis of 3D Cu(OH)₂@NiCo-Binary Hydroxide Core–Shell Nanotube Arrays with High Mass Loading for High-Performance Asymmetric Supercapacitors

Core-shell metallic nanotube arrays for highly sensitive surface-enhanced Raman scattering (SERS) detection

Here, we demonstrate the application of highly ordered, periodic Ag/Au core-shell triangle nanotube arrays as an ultrasensitive and low-cost surface-enhanced Raman scattering (SERS) substrate for the first time. The arrays of core-shell nanotube, with an outer diameter of 1.5 μm, were fabricated using top-down wafer-scale lithography followed by sequential sputter deposition of Ag and Au. The SERS activity of various combinations of core-shell structures was evaluated. It was found that Ag-core nanotubes overlaid with the Au-shell resulted in the highest Raman intensity, where the enhancement factor for R6G as a probe molecule is determined to be 1.38 × 107. Meanwhile, the limit of detections for R6G and ketoprofen analytes was evaluated to be 10−10 and 10−6 M, respectively. Linear correlations between the SERS signal intensities and logarithmical scale of both analytes in different concentrations were also established, ranging 10−4–10−10 and 10−2–10−6 M for R6G and ketoprofen, respectively. The Raman R6G peak intensity mapping suggests our metal nanotube arrays act as effective plasmonic hotspots and, thus, are useful for SERS sensing applications.

Construction of hierarchical NiCoSe@CoS core–shell nanotube arrays for high-performance hybrid supercapacitor

In this work, core–shell [email protected] nanotube arrays directly grown on nickel foam were synthesized via two-step hydrothermal method combined with cyclic voltammetry electrodeposition. In such heterostructures, NiCoSe nanotubes as the core were wrapped by interconnected CoS nanosheets as the shell. Results showed that the obtained [email protected] nanotube arrays formed a conductive 3D network by growing CoS nanosheets on the surface of the NiCoSe nanotubes, which increased electroactive sites, shortened ion diffusion pathways, and thus enhanced charge storage. The unique core–shell heterostructures improved the structural stability and accelerated the electrode reaction kinetics of the nanotube arrays. Compared with the single-phase CoS nanosheets and NiCoSe nanotube arrays, the [email protected] nanotube arrays as electrodes demonstrated enhanced areal capacitance (3.28 and 2.22 F cm−2 at 3 and 30 mA cm−2, respectively) and cyclic stability (capacity retention rate of 93 % after 5000 cycles at 3 mA cm−2). Furthermore, the [email protected] nanotube arrays were used as the positive electrode to assemble hybrid supercapacitor devices with carbon nanotubes as the negative electrode. The fabricated device can deliver an energy density of 36.3 Wh kg−1 at a power density of 801.7 W kg−1 with long-term cycling stability, which indicates that the [email protected] nanotube arrays have a greatly practical application value in supercapacitor devices.

Space-controllable TiO2@IrO2 core-shell nanotube array as a bio-interface electrode

This study develops a wet chemical approach to fabricate space-controllable TiO2@IrO2 core@shell nanotube arrays. The process begins with the space-controlling anodization of the TiO2 nanotube array, followed by a chemical bath deposition of IrO2. IrO2 uniformly covers the nanotubular TiO2 with a thickness range of 8– 15 nm. Charge storage capacity (CSC) and electrochemical impedance spectroscopy (EIS) are performed to evaluate the TiO2@IrO2 core-shell nanotube array as an electrode for neural activity application. Electron microscopy images confirm the formation of uniform IrO2 films on both inner and outer nanotube surfaces. An X-ray diffraction pattern shows a good crystallinity of the TiO2@IrO2 core-shell nanotube array. The TiO2@IrO2 core-shell nanotube array presents a large charge storage capacity of 42.84 mC/cm2 attributed to the high-aspect-ratio tubular nanostructure with a conformal IrO2 deposition. Additionally, the TiO2@IrO2 core-shell nanotube array exhibits stability, durability, and good biocompatibility.

Construction of Hierarchical NiCoSe@CoS Core–Shell Nanotube Arrays for High-Performance Hybrid Supercapacitor

Construction of Hierarchical NiCoSe@CoS Core–Shell Nanotube Arrays for High-Performance Hybrid Supercapacitor

Vertical-aligned Ni/NiO core–shell nanotube arrays with high performance for pseudocapacitance and lithium ion storage

Vertical-aligned Ni/NiO core–shell nanotube arrays with high performance for pseudocapacitance and lithium ion storage

Introducing oxygen vacancies for improving the electrochemical performance of Co9S8@NiCo-LDH nanotube arrays in flexible all-solid battery-capacitor hybrid supercapacitors

In this work, rich oxygen vacancies are obtained in Co9S8@NiCo-LDH core-shell nanotube arrays (NTAs), which boost its electrochemical energy storage performance. The flexible carbon cloth (CC) supported Co9S8@NiCo-LDH NTAs are synthesized by situ growth and electrodeposition method. After reacting with NaBH4, the rich oxygen vacancies are generated in NiCo-LDH nanosheets to obtain Co9S8@oxygen vacancies-NiCo-LDH NTAs (Co9S8@OV-NiCo-LDH NTAs). These oxygen vacancies increase the charge transfer rate in the multi-level redox processes and make the electrochemical performance improve sharply. At a current density of 0.5 A g−1, the mass specific capacity of Co9S8@OV-NiCo-LDH NTAs is up to 1335 C g−1, which is more than four times higher than that of the untreated Co9S8@NiCo-LDH NTAs. In addition, with the prepared Co9S8@OV-NiCo-LDH core-shell NTAs as a positive electrode, along with the negative electrode of activated carbon (AC), a high-performance flexible all-solid battery-capacitor hybrid supercapacitors (HSC) device is assembled. The maximum energy density is up to 101.1 Wh kg−1 when the power density is 800 W kg−1.

Supported Ni@Ni2P Core–Shell Nanotube Arrays on Ni Foam for Hydrazine Electrooxidation

Development of high-performance electrocatalysts requires a judicious selection of intrinsically highly active materials and smart structure engineering of electrodes to maximize active site densit...

Effect of electrolyte solution and deposition methods on TiO2/CdS core–shell nanotube arrays for photoelectrocatalytic application

In this work, TiO2 nanostructure thin films were deposited by using anodization technique, while CdS thin films were deposited on TiO2 films by two methods chemical bath deposition (CBD) and successive ionic layer adsorption and reaction (SILAR). The structure of TiO2/CdS films were investigated and analyzed by XRD, SEM, and AFM, but the optical properties were investigated by UV–visible spectroscopy, PL spectroscopy, and spectral response. XRD analysis of all deposited films has confirmed the formation of two phases one is tetragonal phase (anatase, and rutile) for TiO2, and second hexagonal phase which belong to CdS layer. SEM images of TiO2 nanotubes arrays (NTAs)/CdS showed the TiO2 NTs walls become decorated with aggregates of fine CdS nanoparticles that partly penetrate into the TiO2 NTAs pores. AFM measurements displayed increase in the surface roughness compared with TiO2 films. PL measurement results of TiO2/CdS core–shell show two peaks, one is located at UV-region pointed to energy band gap for TiO2 nano films, and second one is located at visible region pointing to recombination of photogenerated electron–hole pairs within CdS layers. Spectral response measurements showed photocurrent peaks for all TiO2/CdS films deposited with different electrolyte solution have red-shift to visible region. When illuminated with a UV–Vis light source, the TiO2/CdS core–shell films displayed high response. A higher response to UV–Vis light was attained with the use of TiO2 NTAs/CdS films prepared by anodization /CBD. This approach offers a technique for fabricating photoelectrodes.

Metal organic framework derived CoS2@Ni(OH)2 core-shell structure nanotube arrays for high-performance flexible hybrid supercapacitors

The rational design of hybrid structures which consist of multiple components with distinctive characteristics is an effective strategy for developing materials when energy storage applications. In this paper, a novel hierarchical CoS2@Ni(OH)2 core-shell nanotube array covered carbon cloth is successfully designed and synthesized for use in supercapacitors (SCs). The CoS2 nanotube (NT) arrays are synthesized using the metal organic framework template method, and serve as the scaffold for the growth of ultrathin Ni(OH)2 nanosheets via the electrodeposition process. The optimized CoS2@Ni(OH)2 hybrid electrode exhibits high specific capacity of 743 C g−1 at current density of 1 A g−1, which is nearly 5.9 times higher than that of a single CoS2 electrode. In addition, a solid state hybrid supercapacitor device is fabricated with CoS2@Ni(OH)2 hybrid electrode as positive and activated carbon as negative. The as-prepared devices deliver high energy density (29.22 W h kg−1 at 899.2 W kg−1) and high power density (8.99 kW kg−1 at 11.74 W h kg−1), as well as good cycling stability (85.5% retention of specific capacitance after 3000 cycles). The devices also display excellent flexible properties under different bending conditions. The present work shows that electrode materials with hybrid structure have considerable application prospect for flexible energy storage and conversion.

Construction of core-shell heterojunction regulating α-Fe2O3 layer on CeO2 nanotube arrays enables highly efficient Z-scheme photoelectrocatalysis

Designing direct Z-scheme photocatalytic systems with core-shell architecture is crucial for effective charge separation towards sustainable photocatalysis. Herein, the core-shell heterojunction photocatalyst consisting of α-Fe2O3 nanoparticle layers encapsulating CeO2 nanotube arrays (Ce@Fe) was successfully synthesized through a simple and feasible strategy. The Ce@Fe heterojunctions exhibit the enhanced solar light scattering and absorption performance from 380 nm to 490 nm. The formed direct Z-scheme band structure between CeO2 and α-Fe2O3 further promotes the efficiency of carrier separation and transfer, and the core-shell nanotube array structure provides high specific surface area for antibiotic adsorption and enhanced light scattering, significantly improving the photoelectrocatalytic activity. Impressively, the unique photoelectrode achieves the highest pollutant removal efficiency of 88.6% for photoelectrocatalytic tetracycline degradation at 1 h under full light irradiation, and affords superior stability and strong alkaline resistance, which is expected to photoelectrocatalytic degrade antibiotics with high efficiency and environmental protection in harsh environment. Furthermore, the novel photoelectrocatalytic mechanism involving transfer behaviors of charge carriers, generation of reactive species, degradation intermediate products of tetracycline can be adopted after growing α-Fe2O3 layers onto CeO2 nanotube arrays, in accordance with direct Z-scheme mechanism.

Design of FeCo2S4@Ni(OH)2 core-shell hollow nanotube arrays on carbon paper for ultra-high capacitance in supercapacitors

In this paper, we design a novel FeCo2S4@Ni(OH)2 core-shell hollow nanotube arrays on carbon paper for superior capacitance of supercapacitors. FeCo2S4 hollow nanotube arrays vertically grow on carbon paper via hydrothermal reaction served as a “core” to shorten the ion transport path, Ni(OH)2 nanosheets modified on the hollow nanotube arrays based on constant voltage electrodeposition reveal outstanding pseudocapacitance characteristic. The ultrathin Ni(OH)2 nanosheets act as a “shell” layered to expand the specific surface area, effectively increasing the active sites of the faraday reaction. The subtle heterogeneous synergistic effects significantly improve their electrochemical performance. The unique core-shell structure of FeCo2S4@Ni(OH)2 displays a superior capacity of 239.72 mA h g−1 at 1 A g−1, even at 8 A g−1 still has a capacity of 128.0 mA h g−1, indicating the excellent rate performance. Significantly, the asymmetric supercapacitor assembled by the FeCo2S4@Ni(OH)2 nanoarrays positive electrode and activated carbon (AC) negative electrode exhibits superior electrochemical performance with ultra-high energy density (55.33 Wh Kg−1 at 800 W kg−1) and power density (8000 W kg−1 at 15.78 Wh Kg−1). After 10000 charge-discharge cycles, the device still has capacitance retention of 93.8%. Therefore, FeCo2S4@Ni(OH)2 nanoarrays can be widely used in high-performance supercapacitors as potential and promising electrode materials.

Construction of porous interface on CNTs@NiCo-LDH core-shell nanotube arrays for supercapacitor applications

Carbon-based materials have always been a research hotspot in the field of supercapacitors due to their unique stability under a wide range of potential. However, most of carbon-based materials used in supercapacitors cannot maximize the intrinsic capacitance performance due to the limited internal mass transfer. Herein, hierarchical well-aligned nanotube arrays with porous diffusive interfaces are in-situ fabricated by the self-templated effect of ZnO nanorod and ZIF-8 nano-shell. In this unique architecture, the well-aligned carbon nanotubes (CNTs) growing firmly on carbon fibers (CFs) can not only improve the mass transfer of ions onto the NiCo-LDHs surfaces, but also used as good backbones for the subsequent loading of NiCoLDHs nanosheets with high capacity. The optimized core-shell electrode displays an excellent capacity of 176.33 mAh g−1 at 1 A g−1. The as-prepared CNTs@NiCo-LDH//ZIF-8 derived carbon asymmetric supercapacitor (ASC) exhibits a high energy density of 37.38 Wh kg−1 at 800 W kg−1 and an outstanding cycling stability (90.22% retention after 5200 cycles), which offers a new synthesis strategy for design of carbon-based materials in superior electrochemical energy storage applications.

MoS2 Decorated on Different Metal Oxide Nanotubular Structures with a High Density of Reactive Sites for HER Reactions

MoS2 is intensively investigated for decades owing to some unique chemical and physical properties. 1 For many applications, the use of nanoscale geometries is highly advantageous owing to the high specific surface area and short carrier and ion diffusion pathways that can be established.2 This is to a large extent due to the weak van der Waals force between the stacked S-Mo-S units giving it a graphene-like layer structure. 3 This is not only the origin of outstanding lubrication properties but also the key to the insertion and extraction of small foreign ions into the free space of the S-Mo-S layers.4 In this study, we report the self-organized formation of anodic molybdenum oxide nanotube arrays.5 The amorphous tubes can be crystallized to MoO2 or MoO3 and be converted fully or partially into molybdenum sulfide. Vertically aligned MoOx/MoS2 nanotubes can be formed with defined MoS2 sheets in a layer by layer arrangement. These provide a high density of reactive stacking misalignments (defects). These core–shell nanotube arrays consist of a conductive suboxide core and a functional high defect density MoS2 coating. Such structures are investigated for applications in electrocatalysis (hydrogen evolution). Furthermore, nanoscaled MoS2 has a gap broadens up to 1.8 eV when reaching monolayer thickness with a conduction band more negative to the conduction band of TiO2. In our experiments, MoS2 can be decorated on the top of anodic anatase TiO2 nanotubes (TiNTs) site-selectively. 6 The layers can be used as co-catalysts for photocatalytic hydrogen evolution. A strongly enhanced H2 evolution activity can be observed using only a nominal 1 nm thick MoS2 decoration on top of a 6 μm thick TiNT layer. We ascribe this strong beneficial effect to two factors: (i) the thin molybdenum sulfide on the top acts as an electron transfer mediator, i.e. as an H2 evolution co-catalyst; and (ii) the underlying tube layer acts as a light-to-electron harvester.

Fabrication of Core-Shell Nanotube Array for Artificial Photosynthesis Featuring an Ultrathin Composite Separation Membrane.

Macroscale arrays of cobalt oxide-silica core-shell nanotubes with high aspect ratio and ultrathin walls of less than 20 nm have been fabricated. The silica shells feature embedded oligo-para(phenylenevinylene) molecules for charge transport across the insulating silica layer, which is tightly controlled by their electronic properties. The assembly is based on the use of a sacrificial Si nanorod array template combined with atomic layer deposition, covalent anchoring of organic wire molecules, and dry cryo-etching. High-resolution TEM imaging of samples prepared by microtome affords structural details of single core-shell nanotubes. The integrity of silica-embedded organic wire molecules exposed to atomic layer deposition, thermal treatment, and harsh etching procedures is demonstrated by grazing angle ATR FT-IR, FT-Raman, and XPS spectroscopy. The inorganic oxide-based core-shell nanotubes with ultrathin gas-impermeable, proton-conducting silica shells functionalized by molecular wires enable complete nanoscale photosynthetic units for CO2 reduction by H2O under membrane separation. Arrays of massive numbers of such core-shell nanotube units afford a design that extends the separation of the incompatible H2O oxidation and CO2 reduction catalysis environments across the continuum of length scales from nanometers to centimeters.

Highly efficient biosensors by using well-ordered ZnO/ZnS core/shell nanotube arrays

We have studied the fabrication of highly efficient glucose sensors using well-ordered heterogeneous ZnO/ZnS core/shell nanotube arrays (CSNAs). The modified electrodes exhibit a superior electrochemical response towards ferrocyanide/ferricyanide and in glucose sensing. Further, the fabricated glucose biosensor exhibited good performance over an acceptable linear range from 2.39 × 10−5 to 2.66 × 10−4 mM, with a sensitivity of 188.34 mA mM−1 cm−2, which is higher than that of the ZnO nanotube array counterpart. A low limit of detection was realized (24 μM), which is good compared with electrodes based on conventional structures. In addition, the enhanced direct electrochemistry of glucose oxidase indicates the fast electron transfer of ZnO/ZnS CSNA electrodes, with a heterogeneous electron transfer rate constant (Ks) of 1.69 s−1. The fast electron transfer is attributed to the high conductivity of the modified electrodes. The presented ZnS shell can facilitate the construction of future sensors and enhance the ZnO surface in a biological environment.

NiCo2S4@PPy core-shell nanotube arrays on Ni foam for high-performance supercapacitors

NiCo2S4@PPy core–shell nanotube arrays have been successfully prepared through three facile steps: solvothermal synthesis, solvothermal sulphurisation and subsequent in situ electropolymerisation of polypyrrole (PPy). Their structure and morphology were studied by XRD, FTIR, SEM and TEM. The results suggest that a thin layer of PPy with 8 nm in thickness is wrapped on the surface of NiCo2S4 nanotubes. The coating PPy strong promotes pseudo-capacitance reaction of NiCo2S4 nanotube arrays. NiCo2S4@PPy shows lower charge plateau and IR drop, higher discharge plateau and Coulombic efficiency. Rate performance is improved remarkably. Average specific capacitance at 24 mA cm−2 is even two times that of the uncoated NiCo2S4. The galvanostatic cycling tests at 4 mA cm−2 indicate NiCo2S4@PPy exhibit the highest specific capacitance of 1524 F g−1 and improved capacitance retention to 78.5% after 3000 cycles. The corresponding values of the uncoated NiCo2S4 nanotube arrays are only 1410 F g−1 and 22%. The improved electrochemical performance is mainly attributed to unique core–shell nanotube array structure and the key assistant effect of the coating PPy which remarkably improves the conductive property of NiCo2S4 long nanotubes and effectively enhances structure stability and cycling stability of NiCo2S4 nanotubes.

Design and synthesis of H-TiO2/MnO2 core–shell nanotube arrays with high capacitance and cycling stability for supercapacitors

Constructing hybrid electrodes with pseudocapacitive materials is an efficient strategy to realize high capacitance in supercapacitors for many high-energy applications ranging from portable electronics to consumer devices. However, as a typical pseudocapacitive electrode material, MnO2 usually suffers from poor electronic and ionic conductivities, which hinders the realization of their achievable pseudocapacitances. Comparing with conventional noble metals, cost-effective and robust hydrogenated TiO2 nanotube arrays are an excellent scaffold to support pseudocapacitive materials due to enhanced ion and electron delivery. Benefit from the structural and electronic advances, the well-designed H-TiO2/MnO2 NTAs supercapacitor exhibits specific capacitance as high as ~803 F g−1 at the scan rate of 5 mV s−1, reveals ~88% of the initial capacitance after 20000 cycles (only 0.0006% loss per cycle) and shows a high-rate capability. The well-performed designer could be a promising candidate for future power sources in a wide range of applications.

The fabrication, formation mechanisms and applications of novel nanoporous TiO2 membranes prepared by anodization

In this paper, the TiO 2 nanoporous membranes were prepared by a two-step anodization method on Ti foils. The novel overlapped porous nanostructure, core-shell nanotube arrays and normal nanotubes arrays were successively observed during the anodization process. The formation mechanisms of such novel porous nanostructures were proposed based on the results and analysis of the surface morphology, crystallographic structure, X-ray photoelectron spectroscopy analysis and time-dependent current density curves. The overlapped porous nanostructure may originate from the exponential decay of current density during the initial stage. The nanopore diameter significantly depends on the current density; the large current density causes large nanopores on the top layer and the successive deceased current density results in the small nanopores in the under layer. The core-shell nanotubes arrays structure was suggested to relate with the composition and solubility of the anodized nanotubes. From the inner to the outer, each tube consists of several kinds of titanium oxide layers with different composition and different solubility. With further anodization, the inner layer titanium oxide, with high solubility in the electrolyte, could be gradually dissolved by the solution, which results in the formation of the normal nanotubes arrays. The finally obtained stable TiO 2 nanotube arrays were used as anodes to assemble dye-sensitized solar cells (DSSCs), and the photovoltaic performance of the cells were studied. The cell based on TiO 2 nanotube arrays without any surface modification gives a power conversion efficiency ( η ) up to 5.88%. After treating the TiO 2 nanotube arrays by TiCl 4 sol solution, the efficiency of the assembled cell increases to 8.47%, exhibiting a well prospect in energy conversion.

Controllable Synthesis of TiO2@Fe2O3 Core-Shell Nanotube Arrays with Double-Wall Coating as Superb Lithium-Ion Battery Anodes

Highlighted by the safe operation and stable performances, titanium oxides (TiO2) are deemed as promising candidates for next generation lithium-ion batteries (LIBs). However, the pervasively low capacity is casting shadow on desirable electrochemical behaviors and obscuring their practical applications. In this work, we reported a unique template-assisted and two-step atomic layer deposition (ALD) method to achieve TiO2@Fe2O3 core-shell nanotube arrays with hollow interior and double-wall coating. The as-prepared architecture combines both merits of the high specific capacity of Fe2O3 and structural stability of TiO2 backbone. Owing to the nanotubular structural advantages integrating facile strain relaxation as well as rapid ion and electron transport, the TiO2@Fe2O3 nanotube arrays with a high mass loading of Fe2O3 attained desirable capacity of ~520 mA h g−1, exhibiting both good rate capability under uprated current density of 10 A g−1 and especially enhanced cycle stability (~450 mA h g−1 after 600 cycles), outclassing most reported TiO2@metal oxide composites. The results not only provide a new avenue for hybrid core-shell nanotube formation, but also offer an insight for rational design of advanced electrode materials for LIBs.