Electrochromic properties of porous NiO thin film as a counter electrode for NiO/WO3 complementary electrochromic window

Highly porous nickel oxide (NiO) thin films were prepared on ITO glass by chemical bath deposition (CBD) method. SEM results show that the as-deposited NiO film is constructed by many interconnected nanoflakes with a thickness of about 20 nm. The electrochromic properties of the NiO film were investigated in a nonaqueous LiClO₄–PC electrolyte by means of optical transmittance, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements. The NiO film exhibits a noticeable electrochromic performance with a variation of transmittance up to 38.6% at 550 nm. The CV and EIS measurements reveal that the NiO film has high electrochemical reaction activity and reversibility due to its highly porous structure. The electrochromic (EC) window based on complementary WO₃/NiO structure shows an optical modulation of 83.7% at 550 nm, much higher than that of single WO₃ film (65.5% at 550 nm). The response time of the EC widow is found to be about 1.76 s for coloration and 1.54 s for bleaching, respectively. These advantages such as large optical modulation, fast switch speed and excellent cycle durability make it attractive for a practical application.     

Nanocrystalline NiO thin film anode with MgO coating for Li-ion batteries

The nanocrystalline NiO thin films with the mean size of 30 nm are prepared by pulsed laser reactive ablation in an oxygen ambient and subsequent coated by MgO on the NiO film surface. As compared with bare NiO, coated NiO film electrode heat-treated at 500 °C exhibits excellent structural stability and electrochemical performance. Excellent electrochemical performance, a reversible capacity as high as 650 mAh/g in the range 0.01–3.0 V at high discharge rate of 2C with a high capacity retention up to 150 cycles, could be achieved with MgO-coated NiO films. Preliminary electrochemical cycling measurements show that capacity retention with capacity fading for bare NiO and MgO-coated NiO film electrodes are 0.43 and 0.28% per cycle, respectively, at the discharge rate of 2C after 150 cycles. This result is related to good structural stability of the MgO-coated NiO film as verified by cyclic voltammetric (CV) measurement and scanning electron microscopy (SEM) analysis.     

Simple and rapid synthesis of NiO/PPy thin films with improved electrochromic performance

Nickel oxide/polypyrrole (NiO/PPy) thin films were deposited by a two step process in which the NiO layer was electrodeposited potentiostatically from an aqueous solution of NiCl₂·6H₂O at pH 7.5 on fluorine doped tin oxide (FTO) coated conducting glass substrates, followed by the deposition of polypyrrole (PPy) thin films by chemical bath deposition (CBD) from pyrrole mixed with ammonium persulfate (APS). The NiO/PPy films were further characterized for their structural, optical, morphological and electrochromic properties. X-ray diffraction study indicates that the films composed of polycrystalline NiO and amorphous PPy. Infrared transmission spectrum reveals chemical bonding between NiO and PPy. Rectangular faceted grains were observed from scanning electron microscopy results. The electrochromic (EC) property of the film was studied using cyclic voltammogram (CV), chronoamperometry (CA) and optical modulation. The NiO/PPy presents superior EC properties than their individual counterparts. The coloration/bleaching kinetics (response time of few ms) and coloration efficiency (358 cm²/C) were found to be improved appreciably. The dramatic improvement in electrochemical stability (from about 500 c/b cycles for PPy to 10,000 c/b cycles for NiO/PPy) was observed. This work therefore demonstrates a cost-effective and simple way of depositing highly efficient, faster and stable NiO/PPy electrodes for EC devices.     

Morphology effect on the electrochromic and electrochemical performances of NiO thin films

NiO thin films on ITO substrate were prepared by chemical bath deposition (CBD) and sol–gel method, respectively. The microstructure and morphology of the NiO films were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Both the films have polycrystalline cubic NiO, but have distinct morphology. The CBD NiO thin film with a highly porous structure exhibited a noticeable electrochromic performance. The variation of transmittance was high up to 82% at 550 nm and the coloration efficiency (CE) was calculated to be 42 cm² C⁻¹. The sol–gel NiO thin film with a smoothly compact structure presented 35% and 28 cm² C⁻¹ at 550 nm, respectively. The electrochemical properties of both the NiO thin films were investigated in 1 M KOH electrolyte by means of cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements. The CV and EIS measurements revealed that the CBD NiO thin film had better electrochemical reversibility, higher reactivity and reaction kinetics due to its highly porous structure.     

Hollow microspheres of NiO as anode materials for lithium-ion batteries

NiO hollow spheres are prepared by heating the NiCl₂/resorcinol-formaldehyde (RF) gel in argon at 700 °C for 2 h, and subsequently in oxygen at 700 °C for 2 h. X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) are employed to characterize the structure and morphology of the as-prepared NiO hollow spheres. These hollow spheres have a diameter of about 2 μm, which are composed of NiO particles of about 200 nm. The electrochemical properties of these NiO hollow spheres are investigated to determine the reversible capacity and cycling performance as anode materials for lithium-ion batteries, and the advantages of their hollow spherical morphology to the electrochemical performance are discussed.     

Pine-cone morphology and pseudocapacitive behavior of nanoporous nickel oxide

Nanoporous pine-cone structured NiO powder was prepared by hydrothermally heated homogeneous precipitation method using cetyltrimethylammonium bromide surfactant (CTAB) as a template and urea as hydrolysis controlling agent. The NiO powder sample was characterized by thermogravimetric analysis (TGA), powder X-ray diffraction (PXRD), Brunauer-Emmet-Teller (BET) isotherm, scanning electron microscopy (SEM) and electrochemical measurements. The prepared NiO was found to be crystalline and highly porous in nature with high specific surface area and pore volume. The pseudocapacitance behavior of this material was investigated using cyclic voltammetry, chronopotentiometry and impedance spectroscopic studies employing a three-electrode system in the single cell mode. The SEM analysis reveals hierarchically porous pine-cone morphology for NiO which shows good specific capacitance (∼337 F g⁻¹) measured by cyclic voltammetry. The galvanostatic charge-discharge cycles obtained in chronopotentiometric measurements indicate that the NiO sample exhibits good electrochemical stability. The columbic efficiency of NiO was found to be about 99% after 100 galvanostatic charge-discharge cycles. The impedance spectroscopic studies confirmed that the pseudocapacitance behavior of the porous NiO was a result of OH⁻ ion diffusion processes in the system. In this study, a correlation has been made between the specific capacitance values and physicochemical properties as well as the unique surface morphology of NiO.     

An efficient and non-precious anode electrocatalyst of NiO-modified carbon nanofibers towards electrochemical urea oxidation in alkaline media

Non-precious NiO nanoparticles were combined with carbon fibers (CFs) to design the novel electrode material; NiO-CFs. The as-synthesized NiO-CFs material was investigated in terms of Field emission scanning electron microscope (FE-SEM), Fourier-transform infrared spectroscopy (FT-IR), Brunauer-Emmett-Teller (BET) surface area, Energy-dispersive X-ray spectroscopy (EDX), UV–vis spectra, Transmission electron microscope (TEM), selected area diffraction (SAED) pattern and X-ray diffraction (XRD) techniques. These analyses indicate the successful synthesis of a nanocomposite of NiO-CFs. Cyclic voltammetry (CV) in addition to chronoamperometric (CA) and electrochemical impedance spectroscopy (EIS) methods were studied in the 3-electrodes system to examine the electrochemical performance of NiO-CFs material for urea oxidation in KOH medium. The synthesized nanocomposite showed improved electrochemical oxidation of urea at various urea concentrations up to 1.5 M. The decreasing of both charge transfer impedance and series resistance indicates the enhanced transfer of electrons in the occurrence of urea which could be related to the high electrochemical performance of NiO-CFs material as an electrocatalyst. The superior electrochemical activity can be due to the assembly of C-structure with NiO nanoparticles during the synthesis steps which enhance electrocatalysis, charge transfer, and structural defects.     

Electrochromic properties of Al doped B-subsituted NiO films prepared by sol–gel

In this paper, Al doped B-substituted NiO films were prepared by sol–gel method. The effect of the Al content on the structure of the Al_xB_0.15NiO films were studied with X-ray diffraction (XRD) and transmission electron microscopy (TEM). The electrochemical and EC properties were examined by cyclic voltammetric (CV) measurements and UV–Vis spectrophotometry, respectively. Al doping could prevent the crystallization of the films, which exhibited much better electrochemical and electrochromic properties than undoped samples. The bleached state absorbance could be significantly lowered when the Al added. EC efficiencies measured at λ = 500 nm of the films with different Al doping content reach ～30 cm² C^?1, with a change in transmittance up to 70%.     

Synthesis and Humidity Sensing Properties of NiO Intercalated Polyaniline Nanocomposite

The exercising cooperative and interfacial properties of metal oxide and conducting polymer as a sensing material for humidity detection was the focal point of this study. In this piece of work nano sized NiO and its composite with polyaniline has been prepared. The cooperative effects of NiO on stuructural, morphology, humidity sensing behaviour of PANI has been investigated. Prepared materials were characterized by infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscope (SEM),UV–VIS spectroscopy and Four probe techniques. The result reveals that the NiO strongly influences on polymer chain, crystallinity, stability, electrical and optical properties of PANI, which improves its viability in technology development. Finally, PANI/NiO was used for electrochemical humidity sensing of a closed atmosphere. The result reveals that 100 times increase in sensitivity of PANI due to the presence of NiO nano particles. Finally, the results indicate that the impact of NiO on PANI makes it promising perspective materials for humidity monitoring of closed chamber with improved sensing parameters over several method and materials.     

Battery-like behavior of Ni-ceria based systems: Synthesis,surface defects and electrochemical assessment

NiO, CeO₂ and respective composites are extensively used in energy storage devices due to mostly their high electrochemical activity. However, the assessment of battery-like behavior of Ni-ceria based systems comprising (Ni or Gd)-doped ceria combined with NiO seems to be neglected in the literature. In this work, NiO and ceria-based solid solutions composite powders were obtained by a co-precipitation synthesis method. The structure and particle size of the calcined powders were investigated by X-ray diffractometry (XRD) and field emission scanning electron microscopy (FESEM), respectively. Oxidative states of composites were inspected by X-ray photoelectron spectroscopy (XPS). The electrochemical performance of powders was evaluated by cyclic voltammetry, galvanostatic charge-discharge and impedance spectroscopy. Refinement of the XRD patterns showed that powders have nanosized crystallites and mean size of particles within 20 – 70?nm were revealed by FESEM. The improved specific capacity of the NiO-CeO₂ electrode material (about 2.5 times higher than that of NiO-CGO at 5?mV?s^?1) is due to an increase in Faradic reactions taken place on its surface with a higher fraction of defects (namely Ni³⁺, Ce³⁺ and oxygen vacancies), as determined by XPS. The superior electrochemical performance of the NiO-CeO₂ electrode is also confirmed by electrochemical impedance spectroscopy.     

Enhanced capacitance of a NiO electrode prepared in the magnetic field

The enhancement of the surface alignment by magnetic field had a great theoretical and practical significance in the improvement of electrochemical capacitor. In the present study, the NiO nanowires were synthesized by liquid-phase reduction method, and the electrode was prepared within external magnetic field. The effects of magnetic field on the electrode surface and the electrochemical behavior were investigated. X-ray diffraction and scanning electron microscope studies showed that the applied magnetic field results in an orderly surface structure of the electrode, which induced an effective transfer path for the electrons and ions. Meanwhile, the orderly electrode surface improved the electrochemical capacitance, as well as decreased the internal resistance. It was found on the cyclic voltammetry and galvanostatic charge/discharge measurements that the electrode prepared with the magnetic field displays an increased capacitance (506 F g^?1), high power density (135.8 W kg^?1) and energy density (17.6 Wh kg^?1), and improved cycle stability compared to the electrode without magnetic field. Electrochemical impedance spectroscopy results demonstrated enhanced electrochemical properties for the addition of magnetic field.     

Electrochemical lithium storage of titania nanotubes modified with NiO nanoparticles

The nanotubes of mixed TiO₂(B) and anatase phases, obtained by hydrothermal synthesis and subsequent calcination, are modified with NiO nanoparticles. In the modified products, NiO nanoparticles with poor crystallinity exist inside titania tubes and are attached to the outside surface of the nanotubes according to X-ray diffraction (XRD), transmission electron microscopy (TEM) and energy dispersive X-ray spectra (EDS) analysis. The titania nanotubes, modified with 5 wt.% NiO in which NiO nanoparticles were distributed homogenously, exhibit the optimal cycle performance and a good capability for high rate discharge. The lithium ion diffusion is mainly related to the anatase phase, while the electrochemical reaction activity is attributed to the TiO₂(B) phase. Relative to titania nanotubes, NiO-modified nanotubes have a better electrochemical reaction activity, which is beneficial for the improvement of the high rate charge-discharge capability.     

Capacitive and textural characteristics of polyaniline-platinum composite films

The capacitive behavior of various composite thin films composed of polyaniline (PANI) polymerized by cyclic voltammetry and platinum microparticles deposited by potentiostatic or pulse-rest techniques was systematically compared using cyclic voltammetry and chronopotentiometry. These composite films, exhibiting the highly electrochemical reversibility of redox reactions, high power property and good stability between −200 and 600 mV, were demonstrated to be potential candidates for the electrode materials of electrochemical supercapacitors. The effect of the dispersion degree of Pt particles within the composite films on the electrochemical characteristics and stability of the PANI-Pt composite films was discussed. The crystalline information, surface morphologies and platinum distribution profiles of these organic-inorganic composite films were, respectively, characterized by X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), and Auger electron spectroscopy (AES).     

Spherical NiO-C composite for anode material of lithium ion batteries

Spherical NiO-C composite was prepared by dispersing spherical NiO in glucose solution and subsequent carbonization under hydrothermal conditions at 180 °C. The microstructure and morphology of the NiO-C and NiO powders were characterized by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). The electrochemical properties of the electrodes were measured by galvanostatic charge-discharge tests, cyclic voltammetric analysis (CV), and electrochemical impedance spectroscopy (EIS). SEM images showed that the amorphous carbon not only coated on the surface but also filled the inner pores of the NiO spheres. Electrochemical tests showed that the NiO-C composite exhibited higher initial coulombic efficiency (66.6%) than NiO (56.4%), and better cycling performances. The improvement of these properties is attributed to the carbon, as it can reduce the specific surface area of porous sphere, and enhance the conductivity of porous NiO.     

Catalytic combustion of methane over a highly active and stable NiO/CeO2 catalyst

In the last decades, many reports dealing with technology for the catalytic combustion of methane (CH₄) have been published. Recently, attention has increasingly focused on the synthesis and catalytic activity of nickel oxides. In this paper, a NiO/CeO₂ catalyst with high catalytic performance in methane combustion was synthesized via a facile impregnation method, and its catalytic activity, stability, and water-resistance during CH₄ combustion were investigated. X-ray diffraction, low-temperature N₂ adsorption, thermogravimetric analysis, Fourier transform infrared spectroscopy, hydrogen temperature programmed reduction, methane temperature programmed surface reaction, Raman spectroscopy, electron paramagnetic resonance, and transmission electron microscope characterization of the catalyst were conducted to determine the origin of its high catalytic activity and stability in detail. The incorporation of NiO was found to enhance the concentration of oxygen vacancies, as well as the activity and amount of surface oxygen. As a result, the mobility of bulk oxygen in CeO₂ was increased. The presence of CeO₂ prevented the aggregation of NiO, enhanced reduction by NiO, and provided more oxygen species for the combustion of CH₄. The results of a kinetics study indicated that the reaction order was about 1.07 for CH₄ and about 0.10 for O₂ over the NiO/CeO₂ catalyst.     

Hierarchical NiO nanoflake coated CuO flower core–shell nanostructures for supercapacitor

In this work, we developed a simple and cost-effective approach to prepare the hierarchical NiO/CuO nanocomposite without any surfactant. The morphology and structure of the hybrid nanostructure was examined by focus ion beam scanning electron microscopy (FIB/SEM), X-ray diffraction spectroscopy (XRD) and high-resolution transmission electron microscopy (HRTEM). Furthermore, the electrochemical properties of the hierarchical NiO/CuO nanocomposite electrodes were elucidated by cyclic voltammograms, galvanostatic charge/discharge tests and electrochemical impedance spectroscopy in 6 M KOH electrolyte. The electrochemical results demonstrated that this unique NiO/CuO nanostructure exhibited a specific capacitance of 280 F g⁻¹ and excellent cycling stability (91.4% retention after 3000 cycles). The remarkable electrochemical performance coupled with the facile synthesis of the hierarchical NiO/CuO nanocomposite indicated the great application potential in supercapacitors.     

Electrodeposition of nickel oxide nanoparticles on glassy carbon surfaces: application to the direct electron transfer of tyrosinase

This work describes the performance of a tyrosinase/nickel oxide nanoparticles/glassy carbon (Tyr/NiO NPs/GC) electrode. This electrode was prepared by first applying a NiO NPs electrochemical deposition onto the GC electrode surface and then tyrosinase immobilization was applied to the surface of electrodeposited NiO NPs. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) procedures demonstrated the existence of different NiO NP geometrical structures. These geometrical structures could lead to better immobilization of proteins on their surfaces. The copper containing enzyme tyrosinase successfully achieved electrical contact with the electrode because of the unique structural alignment of tyrosinase enzyme on the nanometer-scale nickel oxide surfaces. This method could be suitable for application to nanofabricated devices facilitating better performance. It was concluded that tyrosinase can be effectively applied to nanometer-scale nickel oxide surfaces.     

Developing high-transmittance heterojunction diodes based on NiO/TZO bilayer thin films

In this study, radio frequency magnetron sputtering was used to deposit nickel oxide thin films (NiO, deposition power of 100 W) and titanium-doped zinc oxide thin films (TZO, varying deposition powers) on glass substrates to form p(NiO)-n(TZO) heterojunction diodes with high transmittance. The structural, optical, and electrical properties of the TZO and NiO thin films and NiO/TZO heterojunction devices were investigated with scanning electron microscopy, X-ray diffraction (XRD) patterns, UV-visible spectroscopy, Hall effect analysis, and current-voltage (I-V) analysis. XRD analysis showed that only the (111) diffraction peak of NiO and the (002) and (004) diffraction peaks of TZO were observable in the NiO/TZO heterojunction devices, indicating that the TZO thin films showed a good c-axis orientation perpendicular to the glass substrates. When the sputtering deposition power for the TZO thin films was 100, 125, and 150 W, the I-V characteristics confirmed that a p-n junction characteristic was successfully formed in the NiO/TZO heterojunction devices. We show that the NiO/TZO heterojunction diode was dominated by the space-charge limited current theory.     

Preparation and electrochemistry of NiO/SiNW nanocomposite electrodes for electrochemical capacitors

This paper studies nickel oxide/silicon nanowires (NiO/SiNWs) as composite thin films in electrodes for electrochemical capacitors. The SiNWs as backbones were first prepared by chemical etching, and then the Ni/SiNW composite structure was obtained by electroless plating of nickel onto the surface of the SiNWs. Next, the NiO/SiNW nanocomposites were fabricated by annealing Ni/SiNW composites at different temperatures in an oxygen atmosphere. Once the electrodes were constructed, the electrochemical behavior of these electrodes was investigated with cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). In 2 M KOH solution, the electrode material was found to have novel capacitive characteristics. Finally, when the NiO/SiNW composites were annealed at 400 °C, the maximum specific capacitance value was found to be as high as 681 F g⁻¹ (or 183 F cm⁻³), and the probing of the cycling life indicated that only about 3% of the capacity was lost after 1000 charge/discharge cycles. This study demonstrated that NiO/SiNW composites were the optimal electrode choice for electrochemical capacitors.     

Electrochemical evaluation of binary Ni2V2O7 nanorods as pseudocapacitor electrode material

Pyrochlore structured nickel vanadate nanorods had been prepared by simple co-precipitation method. It was examined for pseudocapacitor electrode material. Morphological, optical and structural aspects of synthesized materials had been studied using a high-resolution transmission electron microscopy, UV–Visible absorption spectroscopy and powder X-ray diffraction analysis, respectively. The functional groups, stretching and bending vibrations were traced by Fourier transform infrared spectroscopy and the formation of nickel vanadate nanorods was confirmed by the binding energy analysis through X-ray photoelectron spectroscopic studies. The rod-shaped nanostructures of pyro nickel vanadate were confirmed by the scanning electron microscopy and HR-TEM analysis. Electrochemical techniques such as cyclic voltammetry, chronopotentiometry and electrochemical impedance spectroscopy techniques were used to analyse the supercapacitive behaviour of the prepared nanorods. Pyro nickel vanadate nanorods possesses excellent electrochemical stability up to 3000 cycles and the performance retention of about 94.1% was achieved even after 3000 repetitive charge-discharge cycles.