Hollow NiO Research Articles

Multishelled NiO Hollow Spheres Decorated by Graphene Nanosheets as Anodes for Lithium-Ion Batteries with Improved Reversible Capacity and Cycling Stability

Graphene-based nanocomposites attract many attentions because of holding promise for many applications. In this work, multishelled NiO hollow spheres decorated by graphene nanosheets nanocomposite are successfully fabricated. The multishelled NiO microspheres are uniformly distributed on the surface of graphene, which is helpful for preventing aggregation of as-reduced graphene sheets. Furthermore, the NiO/graphene nanocomposite shows much higher electrochemical performance with a reversible capacity of 261.5 mAh g−1at a current density of 200 mA g−1after 100 cycles tripled compared with that of pristine multishelled NiO hollow spheres, implying the potential application in modern science and technology.

Design and synthesis of metal oxide hollow nanopowders for lithium-ion batteries by combining nanoscale Kirkendall diffusion and flame spray pyrolysis

This study introduces an efficient process that combines a gas phase reaction method and nanoscale Kirkendall diffusion for the large-scale production of metal-oxide hollow nanopowders. Core-shell-structured NiO@SiO2 nanopowders prepared by flame spray pyrolysis are transformed into hollow NiO@SiO2 nanopowders via a nanoscale Kirkendall diffusion process. The SiO2 coating layer plays a key role in preventing the sintering and growth of the Ni or NiO nanopowders during the preparation process. The mean size of hollow core and shell thickness of the hollow NiO nanopowders are 11 and 7nm, respectively. At a current density of 0.5Ag−1, the NiO@SiO2 nanopowders with hollow and filled structures exhibit 100th cycle discharge capacities of 885 and 338mAhg−1, respectively. In addition, the hollow NiO@SiO2 nanopowders, which exhibit low charge transfer resistances and fast Li-ion diffusion rates, also show better cycling and rate performance than the nanopowders with filled structures.

Porous and hollow NiO microspheres for high capacity and long-life anode materials of Li-ion batteries

Hollow NiO microspheres with porous shell are synthesized through the ion exchange of a facile zinc citrate template with the subsequent chemical etching. As an anode material for LIBs, the porous hollow NiO electrode shows much higher reversible capacity and better cycling stability in comparison with the ZnO–NiO composite. After 400cycles under a high current rate of 1C, the discharge capacity of the NiO electrode is steadily maintained around 700mAg−1. This excellent high power performance is attributed to the unique hollow and porous nanostructure, which not only increases the speed of mass transport but also accommodates the drastic volume change during the cycling process.

Synthesis of NiO Nanofibers Composed of Hollow Nanospheres with Controlled Sizes by the Nanoscale Kirkendall Diffusion Process and Their Electrochemical Properties.

NiO nanofibers composed of hollow NiO nanospheres with different sizes were prepared by electrospinning method. The mean size of the hollow NiO nanospheres was determined by the mean size of the Ni nanocrystals of the Ni-C composite nanofibers formed as an intermediate product. Porous-structured NiO nanofibers were also prepared as a comparison sample by direct oxidation of the electrospun nanofibers. The discharge capacities of the nanofibers composed of hollow nanospheres reduced at 300, 500, and 700 °C for the 250th cycle were 707, 655, and 261 mA h g(-1), respectively. However, the discharge capacity of the porous-structured NiO nanofibers for the 250th cycle was low as 206 mA h g(-1). The nanofibers composed of hollow nanospheres had good structural stability during cycling.

Facile synthesis of hierarchically structured NiO flower-like hollow spheres

ABSTRACTThe hierarchical flower-like NiO hollow spheres were synthesised by a facile method without using any templates or surfactants. The as-prepared sample and precursor were characterised by X-ray diffraction and field emission scanning electron microscopy. The results indicated that the as-prepared NiO is self-assembled hierarchically. During the assembly of NiO, the reaction time plays an important role. The flower-like NiO hollow sphere showed much higher catalytic activity than large-size NiO or hollow NiO for the oxidative dehydrogenation of ethane to ethylene due to its special structure.

Facile synthesis of Co3O4 nanowires grown on hollow NiO microspheres with superior electrochemical performance

The NiO/Co3O4 core/shell composites as a promising supercapacitor material have been fabricated by facile hydrothermal process. The structure and morphology of the NiO/Co3O4 core/shell composites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results indicated that the NiO hollow spheres were decorated by Co3O4 nanowires, and the nanowires were composed of nanoparticles. Electrochemical properties were characterized by cyclic voltammetry, galvanostatic charge/discharge measurements, and electrochemical impedance spectroscopy. The results suggested that the NiO/Co3O4 core/shell composites had good electrochemical reversibility and displayed superior capacitive performance with large capacitance (510Fg−1). Moreover, NiO/Co3O4 core/shell composites showed excellent cyclic performanceafter 1000 cycles.

Structure–reactivity relationships of Ni–NiO core–shell co-catalysts on Ta2O5 for solar hydrogen production

Ni–NiO core–shell co-catalyst structures on Ta2O5 have been investigated for solar H2 production. Core–shell co-catalysts with different morphologies resulted in large changes in photocatalytic activity. Increased H2 production was found to be related to an increase in the thickness of NiO shell due to suppression of the back reaction. Atomic level transmission electron microscopy showed that the core–shell co-catalyst structures deactivated primarily due to a loss of metallic Ni from the core structure. During deactivation, the catalyst transformed either to structures consisting of NiO nanoblocks or hollow NiO shells. The phase transformations occurring during deactivation were associated with Ni diffusion processes that are driven by light illumination.

Synthesis and electrochemical properties of spherical and hollow-structured NiO aggregates created by combining the Kirkendall effect and Ostwald ripening.

The Kirkendall effect and Ostwald ripening were successfully combined to prepare uniquely structured NiO aggregates. In particular, a NiO-C composite powder was first prepared using a one-pot spray pyrolysis, which was followed by a two-step post-treatment process. This resulted in the formation of micron-sized spherical and hollow-structured NiO aggregates through a synergetic effect that occurred between nanoscale Kirkendall diffusion and Ostwald ripening. The discharge capacity of the spherical and hollow-structured NiO aggregates at the 500(th) cycle was 1118 mA h g(-1) and their capacity retention, which was measured from the second cycle, was nearly 100%. However, the discharge capacities of the solid NiO aggregates and hollow NiO shells were 631 and 150 mA h g(-1), respectively, at the 500(th) cycle and their capacity retentions, which were measured from the second cycle, were 63 and 14%, respectively. As such, the spherical and hollow-structured NiO aggregates, which were formed through the synergetic effect of nanoscale Kirkendall diffusion and Ostwald ripening, have high structural stability during cycling and have excellent lithium storage properties.

Three-Dimensional Nickel Oxide@Carbon Hollow Hybrid Networks with Enhanced Performance for Electrochemical Energy Storage

In this paper, the novel nickel oxide@carbon (NiO@C) hollow hybrid networks (HHNs) consisted of nanotubes with interconnected branches are designed and fabricated via template-assisted electrodeposition method. Electrochemical measurements demonstrate that the NiO@C HHNs electrodes exhibit high specific capacitance (Csp) (572.5F/g) at current density of 2.5A/g, which is more than twice as that of NiO hollow networks (HNs) electrode (259.6F/g). The NiO@C HHNs electrodes show high flexibility and excellent cycle performance (almost no capacitance loss after 2000 cycles) and exhibit superior rate capability (∼14%Csp decay with scan rate increasing from 5 to 100mV/s). The assembled asymmetric supercapacitors (ASCs) based on NiO@C HHNs as positive electrodes and 3D active carbon (AC) as negative electrodes also shows high specific capacitance, excellent cycle performance, and high energy and power densities. Two ASC device units connected in series could drive a red light-emitting diode (LED, 2.0V) well for more than 60s after charging at 28A/g for 10s. The above results indicate that the NiO@C HHNs own promising potential for electrochemical energy storage.

Nickel Oxide Nanoparticle-Assembled Microspheres with a High Rate Capability for Lithium Storage

This paper presents the massive preparation of nickel oxide nanoparticle-assembled mesoporous microspheres using acid-treated carbon microspheres as sacrificial templates. The microstructure and morphology of the hollow NiO microspheres are characterized by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, and N2 adsorption–desorption methods. Scanning electron microscopy and transmission electron microscopy images reveal that these hollow spheres are assembled by NiO particles with sizes of ~20 nm. The nickel oxide nanoparticle-assembled mesoporous microspheres feature high surface area and good electronic conductivity, leading to high capacity and excellent cycling performance as anode materials for lithium-ion batteries.

Enhanced ethanol sensing characteristics of In2O3-decorated NiO hollow nanostructures via modulation of hole accumulation layers.

In this work, we report a dramatic enhancement in ethanol sensing characteristics of NiO hollow nanostructures via decoration with In2O3 nanoclusters. The pure NiO and 1.64-4.41 atom % In-doped NiO and In2O3-decorated NiO hollow spheres were prepared by ultrasonic spray pyrolysis, and their gas sensing characteristics were investigated. The response (the ratio between the resistance in gas and air) of the In2O3-decorated NiO hollow spheres to 5 ppm ethanol (C2H5OH) was 9.76 at 350 °C, which represents a significant improvement over the In-doped NiO and pure NiO hollow spheres (3.37 and 2.18, respectively). Furthermore, the 90% recovery time was drastically reduced from 1880 to 23 s, and a selective detection of ethanol with negligible cross-response to other gases was achieved. The enhanced gas response and fast recovery kinetics were explained in relation to the thinning of the near-surface hole accumulation layer of p-type NiO underneath n-type In2O3, the change of charge carrier concentration, and the variation of oxygen adsorption.

Synthesis of hollow nickel oxide nanotubes by electrospinning with structurally enhanced lithium storage properties

We report a simple electrospinning synthesis method to prepare hollow NiO nanotubes composed of interconnected nanoparticles. The synthesized NiO nanotubes show diameters of 250–300nm. As an anode material for lithium-ion batteries, the resultant hollow NiO nanotubes exhibit high capacity and good cycle stability (726mAhg−1 at 0.2C up to 150 cycles), as well as good rate capability. The hollow nanotube structure possesses the following features: high NiO-electrolyte contact area, fast Li ion diffusion and better accommodation of volume change. It suggests that the hollow NiO nanotube is a promising anode material for high energy density lithium-ion batteries.

Facile growth of hollow porous NiO microspheres assembled from nanosheet building blocks and their high performance as a supercapacitor electrode

Self-assembled hollow flowerlike NiO as a promising supercapacitor material has been fabricated by a facile hydrothermal process and the formation mechanism of the flowerlike morphology is investigated. The structure and morphology of the NiO samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) etc. and the surface area of the NiO sample was analyzed by measuring its N2 adsorption–desorption isotherms. The results indicated that the addition of P123 inhibited the grain growth of NiO, and with the assistance of P123, the nanoparticles assembled into flowers. The electrochemical properties were characterized by cyclic voltammetry, galvanostatic charge/discharge measurements, and electrochemical impedance spectroscopy. The results suggest that the flowerlike NiO has good electrochemical reversibility and displays superior capacitive performance with large capacitance (619 F g−1), as well as excellent cycling stability after 1000 cycles.

One‐Step Fabrication of Unique Mesoporous NiO Hollow Sphere Film on FTO for High‐Performance P‐Type Dye‐Sensitized Solar Cells

P‐type dye sensitized solar cells (p‐DSCs) deliver much lower overall efficiency than their inverse model, n‐DSCs. However, they have fundamental and practical significance, in particular, their tandem structured solar cells with both p‐ and n‐photoelectrodes could offer great potential to significantly improve the efficiency of existing solar cells. A facile and environmentally friendly method is developed to directly one‐step grow hollow NiO spherical structures on fluorine‐doped tin oxide (FTO) substrate, in which a Ni2+ and polymer complex spherical structure is self‐constructed through a controlled solvent evaporation process, followed by calcination‐converting to a unique NiO hollow sphere film. The prepared material is further used as a photocathode in p‐type dye sensitized solar cells, resulting in 41% increase of an open‐circuit voltage and 18% enhancement of power conversion efficiency than NiO nanoparticles photocathode. The improved performance can be ascribed to suppressed charge recombination at the photocathode/electrolyte interface. This template‐free approach could be universally used to fabricate other nanostructured hollow spheres for a wide range of energy conversion applications such as electrochemical capacitors, chemical sensors, and electrochromic devices.

Preparation and electrochemical characteristics of porous hollow spheres of NiO nanosheets as electrodes of supercapacitors

Porous hollow nanospheres (or spherical shells) made of NiO nanosheets are synthesized and tested for the electrochemical performance of the electrodes made of these materials for supercapacitors. Preparation of the NiO sheet hollow spheres starts with synthesis of polystyrene nanospheres with carboxyl groups (CPS), followed by a two-step activation procedure and the subsequent nucleation and growth by electroless deposition of Ni on the CPS core to obtain CPS@Ni core–shell nanoparticles. The CPS core is eliminated and metallic Ni nanoshell is converted into NiO by calcinations at high temperatures. The material properties of as-prepared hollow NiO nanospheres are characterized by TEM, XRD and N2-absorption measurements. The electrochemical characteristics of the electrodes made of these nanostructured NiO materials are determined by the CV and galvanostatic measurements. These electrochemical tests indicate that electrodes made of the NiO nanosheet hollow spheres exhibit an improved reversible capacitance of 600 F g−1 after 1000 cycles at a high current density of 10 A g−1. It is believed that the good electrochemical performance of these electrodes is attributed to the improved OH− transport in the porous network structures associated with the hollow spheres of randomly oriented NiO nanosheets.

Micelle templated NiO hollow nanospheres as anode materials in lithium ion batteries

A hollow NiO nanosphere constructed electrode exhibits high charge–discharge capacities, cycling and rate performance in lithium ion rechargeable batteries.

Synthesis of Hollow and Hierarchical NiO Nanosheets Nanotubes and their Application as Supercapacitor Electrodes

Hollow and hierarchical NiO nanosheets nanotubes were successfully prepared through a one-step solvothermal route followed by a thermal annealing treatment. The microstructure and chemical composition of Ni-precursor@PNT core-shell nanostructures and calcined NiO nanosheets nanotubes are investigated by SEM, TEM, TGA and XRD. The unique NiO nanosheets nanotubes show admirable electrochemical performance as an electrode material for supercapacitors owing to the hierarchically tubular structures and hollow interior.

Hollow NiO nanotubes synthesized by bio-templates as the high performance anode materials of lithium-ion batteries

Abstract Hollow NiO nanotubular material is prepared by a facile bio-template engaged route using filter paper as the template for Li-ion batteries and optimizing the reaction conditions. The as-obtained products keep the structure of filter paper, resulting in the formation of hollow NiO nanotube aggregates with strong framework and loose hollow mesoporous structure. As anode material for lithium ion batteries, it exhibits a stable reversible capacity of 620 mA h g−1 and keeps over 600 mA h g−1 after 100 cycles except for the first cycle at current density of 200 mA g−1. The NiO eletrode also exhibits good rate capability. The nanostructured characteristics of NiO particles embedded in the nanotube ensure the high capacity in the electrode. The unique hollow structures can shorten the length of Li-ion diffusion and offer a sufficient void space, which sufficiently alleviates the mechanical stress caused by volume change. Herein, the hollow NiO nanotubular electrode exhibits excellent electrochemical performance.

Formation and stability of small well-defined Cu- and Ni oxide particles

Well-defined and -structured Cu/Cu2O and Ni/NiO composite nanoparticles have been prepared by physical-vapor deposition on vacuum-cleaved NaCl(001) single crystal facets. Epitaxial growth has been observed due to the close crystallographic matching of the respective cubic crystal lattices. Distinct particle morphologies have only been obtained for the Ni/NiO particles, comprising truncated half-octahedral, rhombohedral- and pentagonal-shaped outlines. Oxidation of the particles in the temperature range 473–673 K in both cases led to the formation of well-defined CuO and NiO particles with distinct morphologies. Whereas CuO possibly adopts its thermodynamical equilibrium shape, NiO formation is accompanied by entering a Kirkendall-like state, that is, a hollow core–shell structure is obtained. The difference in the formation of the oxides is also reflected by their stability under reducing conditions. CuO transforms back to a polycrystalline mixture of Cu metal, Cu2O and CuO after reduction in hydrogen at 673 K. In contrast, as expected from theoretical stability considerations, the formation of the hollow NiO structure is reversed upon annealing in hydrogen at 673 K and moreover results in the formation of a Ni-rich silicide structure Ni3Si2. The discussed systems present a convenient way to tackle and investigate various problems in nanotechnology or catalysis, including phase transformations, establishing structure/activity relationships or monitoring intermetallic particles, starting from well-defined and simple models.

Template‐Free Fabrication of Hollow NiO–Carbon Hybrid Nanoparticle Aggregates with Improved Lithium Storage

Hollow NiO–carbon hybrid nanoparticle aggregates are fabricated through an environmental template‐free solvothermal alcoholysis route. Controlled hollow structure is achieved by adjusting the ratio of ethylene glycol to water and reaction time of solvothermal alcoholysis. Amorphous carbon can be loaded on the NiO nanoparticles uniformly in the solvothermal alcoholysis process, and the subsequent calcination results in the formation of hollow NiO–C hybrid nanoparticle aggregates. As anode materials for lithium‐ion batteries, it exhibits a stable reversible capacity of 622 mAh g−1, and capacity retention keeps over 90.7% after 100 cycles at constant current density of 200 mA g−1. The NiO–C electrode also exhibits good rate capabilities. The unique hollow structures can shorten the length of Li‐ion diffusion and offer a sufficient void space, which sufficiently alleviates the mechanical stress caused by volume change. The hybrid carbon in the particles renders the electrode having a good electronic conductivity. Here, the hollow NiO‐C hybrid electrode exhibits excellent electrochemical performance.