Nanowall Arrays Research Articles

Self-standing porous LiMn2O4 nanowall arrays as promising cathodes for advanced 3D microbatteries and flexible lithium-ion batteries

Three-dimensional self-supported cathode nanoarchitectures are the key to develop high-performance thin film lithium-ion microbatteries and flexible lithium-ion batteries. In this work, we have developed a facile “hydrothermal lithiation” strategy to prepare vertically aligned porous LiMn2O4 nanowall arrays, comprising highly crystallized spinel nanoparticles, on various conductive substrates without high temperature treatment. The “hydrothermal lithiation” can effectively convert Mn3O4 spinel nanowall arrays into LiMn2O4 spinel nanowall arrays without severe morphology change. The binder-free three-dimensional porous LiMn2O4 nanowall arrays exhibit high specific reversible capacity up to 131mAhg−1 (or 0.29mAhcm−2) as well as outstanding cycling stability and rate capability, making them promising as cathodes for both three-dimensional thin film lithium-ion microbatteries and flexible lithium-ion batteries. A flexible lithium-ion full cell is demonstrated by using LiMn2O4 nanowall arrays on carbon cloth as the cathode and Li4Ti5O12 nanowall arrays on carbon cloth as the anode. The flexible Li4Ti5O12//LiMn2O4 full cell device, employing three-dimensional nanoarchitectures for both cathode and anode, can deliver specific reversible capacities of 124.8mAhg−1 (based on the weight of cathode material) at 1C and 92.1mAhg−1 at 20C with excellent cycle performance. Our work demonstrates the great potential for flexible energy storage technology using low cost fabrication method of nanoarchitectures.

Black mesoporous Li4Ti5O12−δ nanowall arrays with improved rate performance as advanced 3D anodes for microbatteries

3D black mesoporous Li4Ti5O12−δ nanowall arrays with greatly enhanced rate performance are fabricated as promising anodes for advanced lithium-ion microbatteries.

Enhanced lithium storage capabilities of NiO@Si core–shell nanowall arrays by voltage-control technique and their use as anode materials for lithium-ion batteries

In this work, we demonstrate the synthesis of Ni–Li2O@Si core–shell nanowall arrays through the lithiation of pre-synthesized NiO@Si core–shell nanowall arrays during the first lithium insertion process.

Al/C/MnO2 sandwich nanowalls with highly porous surface for electrochemical energy storage

Hierarchical materials supported on metal substrates present promising applications in flexible energy storage and conversion devices. Compared to Au, Ag, Cu, Ni, Ti, W and their alloys, Al, the most abundant metal in the crust has been less used in supercapacitors due to its high activity which makes it unstable in acid and base electrolytes. In this paper, we explore a novel Al/C/MnO2 sandwich structured material for the first time for supercapacitor. Owing to the highly porous and open surface structure and the highly conductive Al/C double core current collector on nanoscale, the Al/C/MnO2 sandwich nanowall arrays supported on Al foil show excellent capacitance performance with a maximum area specific capacitance of 1008.3 mF cm−2 and a high energy density of 35.2 μWh cm−2 at 2 mA cm−2. Moreover, a supercapacitor device with 4 supercapacitors connected in series can power a LED lamp. The present study demonstrates a novel electrode architecture based on Al foil with remarkably high area specific capacitance and stability for promising supercapacitor applications. Our strategy provides a new approach to the fabrication of hierarchical electrode materials from Al metal (could also be extend to other metal substrates) for supercapacitors and other energy storage and conversion devices.

Nanowire interwoven NiCo2S4 nanowall arrays as promising anodes for lithium ion batteries

Metal sulfides have recently emerged as a new class of anode materials for lithium ion batteries. In this work, a facile method based on anion exchange reaction is reported to prepare nanowire interwoven NiCo2S4 nanowall arrays through topotactical transformation from the Ni–Co carbonate hydroxide precursor. The nanowire interwoven NiCo2S4 nanowall arrays are investigated as binder free anodes for lithium ion batteries. The electrochemical measurements reveal that the NiCo2S4 nanowall arrays possess large reversible capacity, good cycling stability and good rate capacity, making them promising anodes for advanced lithium ion batteries.

Ultraviolet lasing action in aligned ZnO nanowall

A vertically aligned ZnO nanowall arrays have been synthesized on a patterned ZnO buffer layer using an interference laser beam. The average height and thickness of the ZnO nanowall were 4 μm and 200 nm, respectively. Room-temperature ultraviolet (UV) lasing was obtained from single piece of ZnO nanowall detached from the substrate. The threshold power density for lasing was estimated to be about 80 kW/cm2. In addition, UV lasing from vertically aligned ZnO nanowall was also observed owing to the presence of holes. The lasing spectra had no regularity in the mode spacing and many different spatial modes, suggesting that the action was supported by the random lasing mechanism. The threshold power density for lasing was about 300 kW/cm2, which was much higher than that of the single piece of ZnO nanowall because of the leakage of the light into buffer layer.

Edge promoted ultrasensitive electrochemical detection of organic bio-molecules on epitaxial graphene nanowalls.

We report the simultaneous electrochemical detection of dopamine (DA), uric acid (UA) and ascorbic acid (AA) on three dimensional (3D) unmodified 'as-grown' epitaxial graphene nanowall arrays (EGNWs). The 3D few layer EGNWs, unlike the 2D planar graphene, offers an abundance of vertically oriented nano-graphitic-edges that exhibit fast electron-transfer kinetics and high electroactive surface area to geometrical area (EAA/GA≈134%), as evident from the Fe(CN)6(3-/4-) redox kinetic study. The hexagonal sp(2)-C domains, on the basal plane of the EGNWs, facilitate efficient adsorption via spontaneous π-π interaction with the aromatic rings in DA and UA. Such affinity together with the fast electron kinetics enables simultaneous and unambiguous identification of individual AA, DA and UA from their mixture. The unique edge dominant EGNWs result in an unprecedented low limit of detection (experimental) of 0.033 nM and highest sensitivity of 476.2 µA/µM/cm(2), for UA, which are orders of magnitude higher than comparable existing reports. A reaction kinetics based modeling of the edge-oriented 3D EGNW system is proposed to illustrate the superior electro-activity for bio-sensing applications.

Ultraviolet Lasing from Vertically-Aligned ZnO Nanowall Array

Ultraviolet Lasing from Vertically-Aligned ZnO Nanowall Array

CdS/CdSe core/shell nanowall arrays for high sensitive photoelectrochemical sensors

CdS/CdSe core/shell nanowall arrays are fabricated by a two-step chemical solution method for use in photoelectrochemical sensors. The morphology of the CdS nanowall arrays and contact behavior with substrate can be controlled through varying the solution concentration. A uniform CdSe layer is deposited on the CdS nanowall arrays by a successive ionic layer adsorption and reaction method, and the thickness of CdSe layer can be effectively controlled by changing deposition cycles. It is demonstrated that the light absorption range of the CdS/CdSe core/shell nanowall arrays can almost be extended to the whole visible region. The obviously enhanced photoelectrochemical current for the heterojunction nanowalls is found under illumination of the simulated sunlight compared with that for the bare CdS nanowalls, which increases from 3.78mA/cm2 to of 8.3mA/cm2. The results indicate that a suitable combination of band gap and band alignment can constitute a promising system for a high efficient photoelectrochemical sensor.

Highly sensitive H2S detection sensors at low temperature based on hierarchically structured NiO porous nanowall arrays

NiO porous nanowall arrays have been successfully grown in situ on ceramic tubes by a hydrothermal reaction, combined with a calcination process. With such unique hierarchical pores, the array film sensor displayed excellent sensing performance toward H2S.

A three-dimensional MnO2/graphene hybrid as a binder-free supercapacitor electrode

Highly aligned manganese dioxide (MnO2) nanowall arrays electrodeposited onto Ti sheets are used as substrates to grow graphene (GR) through chemical vapor deposition (CVD), thus forming a three-dimensional (3D) MnO2/GR hybrid composite.

An interface nanostructured array guided high performance electrochemical actuator

Here we report a novel electrochemical actuator using a hierarchically architectured nanostructure electrode. Vertically aligned NiO nanowall arrays, which act as an interface layer, are in situ grown on a free-standing graphene–carbon nanotube hybrid film. The large specific surface area and fast ion transmission channels of this nanostructured array interface enable us to achieve large deformation in quick switching response (18.4 mm per 0.05 s), high strain and stress rates (8.31% s−1, 12.16 MPa s−1) and excellent durability upon 500 000 times continuous operations in air.

Hierarchically structured TiO2@MnO2 nanowall arrays as potential electrode material for high-performance supercapacitors

Abstract We have reported a facile route for the fabrication of TiO2@MnO2 core–shell nanostructures for use as an electrode material, using a simple hydrothermal process for supercapacitor applications. Field-emission scanning electron microscopy and transmission electron microscopy studies confirmed the formation of a MnO2 nanowall shell structure on the core of TiO2 nanorod surfaces. The nanostructured TiO2@MnO2 core–shell was used as an electrode material, which exhibited excellent electrochemical properties with an improved areal capacitance of 22.19 mF cm−2 (TM-3) at a scan rate of 5 mV s−1 in a 1-M Na2SO4 electrolyte solution. Moreover, the electrode material demonstrated excellent performance with long term cycling stability, by retaining 85% of its initial capacitance after 4000 cycles.

Synthesis of Sb2S3 nanowall arrays for high performance visible light photodetectors

By using a facile polyol and template-free refluxing process, we report the successful synthesis of Sb2S3 nanowall arrays (NWAs) on the surface of FTO substrate. The as-synthesized samples were characterized by SEM, TEM, XRD and UV–vis DRS. The NWAs-based photodetector exhibits linear photocurrent characteristics, high stability, excellent reproducible properties, low LDR (linear dynamic range) value of 8.6dB, fast response time of 0.52s and recovery time of 1.11s. The flexible photodetector was also fabricated by simply transferring the NWAs to a transparent PET substrate; it revealed good flexibility and stability. Our results imply that Sb2S3 NWAs are prospective candidates for high-performance nanoscale optoelectronic devices.

Enhanced supercapacitor performance using hierarchical TiO2 nanorod/Co(OH)2 nanowall array electrodes

We report novel hierarchical TiO2 nanorod (NR)/porous Co(OH)2 nanowall array electrodes for high-performance supercapacitors fabricated using a two-step process that involves hydrothermal and electrodeposition techniques. Field-emission scanning electron microscope images reveal a bilayer structure consisting of TiO2 NR arrays with porous Co(OH)2 nanowalls. Compared with the bare TiO2 NRs, the hierarchical TiO2 NRs/Co(OH)2 electrodes showed improved pseudocapacitive performance in a 2-M KOH electrolyte solution, exhibiting an areal specific capacitance of 274.3 mF cm−2 at a scan rate of 5mV s−1. The electrodes exhibited good stability, retaining 82.5% of the initial capacitance after 4000 cycles. The good pseudocapacitive performance of the hierarchical nanostructures is mainly due to the porous structure, which provides fast ion and electron transfer, a large surface area, short ion diffusion paths, and a favourable volume change during the cycling process.

Field enhancement factor and optimal emitter density in a nanowall array

The field emission from carbon nanowalls has excited the interest of researchers as a potential electron source for a variety of device applications. We derive an explicit analytical expression for the field enhancement factor of a nanowall placed in a nanowall array using the “floating cylinder” model. We show that if the thickness of the walls and the distance between them remain invariable while the height of walls becomes taller, the field enhancement factor increases monotonically but never exceeds a certain constant value. We propose an explicit algebraic formula for finding the optimal distance between the nanowalls at which the anode current reaches a maximum. The optimal emitter density depends only on the applied electric field and the work function of the material; it does not depend on the height of nanowalls. We analyze published experimental data and specify the resource to increase the total current.

Anodic Cu₂S and CuS nanorod and nanowall arrays: preparation, properties and application in CO₂ photoreduction.

Copper sulfide semiconductors made from earth-abundant elements have an optical absorption edge at ca. 1.2 eV, nearly ideal for solar energy harvesting. We report the growth and formation mechanism of vertically oriented arrays of copper sulfide nanostructures formed by electrochemical anodization. Key parameters that affect the morphology and phase of the nanostructures are type and strength of electrolyte, anodization voltage and duration. Cu₂S and CuS nanostructures were obtained on both copper foil and copper-coated flexible Kapton substrates, and depending on the anodization parameters, consisted of vertically oriented arrays of nanowalls, nanoleafs or rods with branched nanodendrites. The anodization parameters also controlled the phase and stoichiometry of the nanostructures. p-type conduction for Cu₂S nanostructures and n-type conduction for CuS nanostructures were revealed by admittance spectroscopy and Mott Schottky analysis. We also observed a weak, but nevertheless promising and previously unnoticed, photocatalytic action in copper sulfide nanorod and platelet arrays for the sunlight-driven conversion of CO₂ into CH₄. Under irradiation by AM 1.5G simulated sunlight at room temperature, a CH₄ production rate as high as 38 μmol m(-2) h(-1) was obtained using the copper sulfide nanostructure arrays as stand-alone photocatalysts for CO₂ photoreduction.

Facile synthesis of ZnWO4nanowall arrays on Ni foam for high performance supercapacitors

In this report, ZnWO4 nanowall arrays (NWAs) were grown on Ni foam by a hydrothermal route and investigated for application in supercapacitors for the first time. The resulting NWAs were analyzed by using X-ray diffraction spectroscopy, scanning electron microscopy, and transmission electron microscopy. ZnWO4 NWAs exhibited high electrochemical property with a specific capacitance of 2.5 F cm−2 at a charge and discharge current density of 20 mA cm−2 (1250 F g−1 at current density of 10 A g−1). Furthermore, they showed an excellent cycling ability at different current densities up to 100 mA cm−2, and 92% (2.3 F cm−2) of the initial capacitance remained after 4000 cycles. The open network structure consisting of interconnected ZnWO4 NWAs directly grown on current collectors is advantageous for electron transport and electrolyte diffusion which can facilitate the electrochemical reaction. Our work not only demonstrated a facile hydrothermal method for ZnWO4 NWAs directly grown on Ni foam, but also revealed ZnWO4 to be a promising electrode for high-property supercapacitors.

Large-scale synthesis of Ag–Si core–shell nanowall arrays as high-performance anode materials of Li-ion batteries

We demonstrate the synthesis of Ag–Si core–shell nanowall arrays via a simple displacement reaction and subsequent RF-sputtering deposition.

Microstructure of porous gallium nitride nanowall networks

Porous GaN films consisting of irregular nanowall arrays were heteroepitaxially grown on 6H–SiC(0001) substrates by ion-beam-assisted molecular beam epitaxy at different substrate temperatures. X-ray diffraction, Rutherford backscattering spectrometry, scanning electron microscopy as well as scanning transmission electron microscopy (STEM) were applied to investigate the porous GaN thin films. Special attention was focused on the characterization of the microstructure of the thin films using a Cs-corrected high-resolution STEM. A high crystalline quality of the formed hexagonal GaN nanowalls was demonstrated. Based on the results, a growth mechanism of porous GaN thin films is discussed.