Pristine NiO Research Articles

A facile electrochemical lithiation method to prepare porous nickel oxide electrodes with high electrochromic performance

A facile electrochemical lithiation method was developed in the framework of the wet chemical route, and NiO films with various lithium contents have been successfully prepared. The structure and electrochromic properties were characterized using SEM, HRTEM, XRD, XPS, etc. The results indicate that all NiO films show a porous morphology, and the ratio of Ni3+/Ni2+ increases from 1.12 to 1.46 after electrochemical lithiation. The storage capacity in lithium electrolytes, effective ionic diffusion rate, transmittance modulation, and coloring efficiency are effectively improved. The optimized NiO electrode exhibits an excellent storage capacity of 6.4 mC/cm2 and transmittance modulation at 550 nm of 35.7%, compared to the pristine NiO (Q = 4.4 mC/cm2, ΔT = 24.3%). Two electrochromic devices were respectively assembled with the pristine and lithiated NiO electrodes as the anodic electrochromic layer. The latter exhibits higher transmittance modulation and coloring efficiency, proving that the electrochemical lithiation method is an effective way to prepare high-performance electrochromic devices.

Role of surface defects in the third order nonlinear optical properties of pristine NiO and Cr doped NiO nanostructures

Pristine NiO and 2% Cr doped NiO nanostructures are successfully synthesized by the modified auto–combustion method for the determination and improvement of linear and nonlinear optical behaviours, and for identifying them as suitable materials for optical limiting applications. Vibrational and linear optical properties of both nanostructures are investigated, and structural and morphological studies are carried out using XRD, FE-SEM, and HR-TEM. From the Kubelka-Munk model, the energy band gaps for pristine and doped samples are found to be 3.52 eV and 3.44 eV, respectively. Both pristine as well as Cr-doped NiO nanostructures reveal substantial nonlinear optical behaviour at the excitation wavelength of 532 nm, arising from the presence of strong reverse saturable absorption. The third order nonlinear absorption coefficients have values of the order of 10−10 m/W and 10−6 m/W, under pulsed (5 ns) and continuous wave laser excitations, respectively. These values confirm the suitability of these nanostructures for fabricating efficient optical limiting devices for safeguarding human eyes and optical sensors from hazardous laser radiation.

Synthesis of p-n NiO-ZnO heterojunction for photodegradation of crystal violet dye

Photocatalytic treatment of wastewater utilizing oxides of metals as photocatalysts has merged a subject of major concern. The photocatalytic efficiency can be increased by the separation of electrons and holes formed by the absorption of photons. The development of heterojunction between two semiconductors is one of the methods used for the separation of photo-induced electrons and holes. Herein, we report a p-n NiO-ZnO heterojunction photocatalyst for efficient photodegradation of crystal violet dye. The homogeneous precipitation method was used for the synthesis of p-n NiO-ZnO in this study. The synthesized heterojunction was characterized by XRD, SEM, EDX, and TGA techniques. The aqueous solution of crystal violet dye was used as model wastewater for the evaluation of the photocatalytic efficiency of as-synthesized material. The photocatalytic performance of p-n NiO-ZnO for photodegradation of crystal violet dye was significantly higher than pristine NiO and ZnO. The photocatalytic activities of NiO, ZnO and NiO-ZnO were found in the ratio of 1: 3.8: 7.8, respectively. Similarly, the ratio of photocatalytic activities of 5% NiO-ZnO, 10% NiO-ZnO, and 15% NiO-ZnO was 1: 1.2: 0.8, respectively. The degradation data was analyzed for kinetics analyses using the Langmuir-Hinshelwood mechanism.

Enhanced electrochemical performance of facilely synthesized cobalt doped cubic NiO nanoflakes for supercapacitor application

Being inexpensive, nontoxic and environmental friendly, NiO has caught special attention as a promising electrode material for supercapacitors. We recently reported facile synthesis of porous NiO nanocrystallites for energy storage application. A sophisticated strategy to improve the electrochemical properties of NiO which is a p-type semiconductor is the incorporation of 3d metal ions into it. In this article, we present successful fabrication of highly porous cobalt doped NiO nanostructures through a facile, low cost, one step solution combustion method without a post calcination treatment and demonstrate the influence of cobalt content on structural properties and electrochemical behavior. The thus prepared Co doped NiO samples were systematically characterized by X-ray diffraction, Fourier transform infrared spectroscopy, Field emission scanning electron microscopy, High resolution transmission electron microscopy, X-ray photoelectron spectroscopy, Brunauer-Emmett-Teller measurements, cyclic voltammetry, chronopotentiometry and electrochemical impedance spectroscopy. It was found that the phase structure of pristine NiO remains unaffected by the process of doping. But doping obviously influences the textural and morphological properties, more importantly, enhances the electrochemical properties of pristine NiO. A maximum specific capacity of 746 C/g (specific capacitance of 1244 F/g) was obtained for an optimum cobalt dopant ratio, which is superior to undoped NiO (295 C/g). Moreover, cobalt doped NiO nanostructures exhibited a good rate capability (71 % capacity retention from 1 to 15 A/g) and long term cycling stability (83.7 % after 5000 cycles at 100 mV/s). An asymmetric device fabricated using Co doped NiO electrode as the positive electrode and activated carbon as the negative electrode delivered an energy density of 32.7 Wh/kg at a power density of 261 W/kg.

The preparation of NiCo2O4 nanoboulders and their application in the electrochemical detection of ofloxacin drug

A sensitive electroactive platform relies directly upon the efficient and conductive interface. This work offers a simple and effective method for synthesizing NiCo2O4 using CTAB surfactant, suited for trace-level antibiotic detection. The route realized the controlled growth of tiny NiCo2O4 nanoboulders with an exposed interface. A comparative evaluation of the bimetallic nanostructures with their pristine compositional counterparts, i.e., NiO and Co3O4, supports its superior electrochemical characteristics based on the synergism of strong redox activity and conductivity from the bimetallic components. The NiCo2O4 nanoboulders exhibited strong electrochemical activity when configured as electrode material for detecting ofloxacin (OFL), a common antibiotic. The sensor exhibited excellent working linearity in a low-concentration range of 0.01–5 ​μM with a detection limit of 1 ​× ​10−3 ​μM for OFL. The kinetics of the NiCo2O4 further supported the electrocatalytic oxidation of OFL to be diffusion controlled with an estimated diffusion coefficient of 2.03310−6 ​cm2 ​s−1. Moreover, the constructed sensor is applicable for detecting OFL from environmental samples, reflecting its workability in complex real-environment.

Nickel Site Modification by High-Valence Doping: Effect of Tantalum Impurities on the Alkaline Water Electro-Oxidation by NiO Probed by Operando Raman Spectroscopy.

In an effort to support the large-scale implementation of clean hydrogen in industry and society, the electrolytic decomposition of water is considered a realistically enticing prospect, provided the guarantee of affordable and durable material components. Within alkaline systems, earth-abundant electrocatalysts could provide both these requirements. However, a continued exploration of the reactivity and the causes behind different behaviors in performance are necessary to guide optimization and design. In this paper, Ta-doped NiO thin films are prepared via DC magnetron sputtering (1–2–4 at % Ta) to demonstrate the effect of surface electronic modulation by non-3d elements on the catalysis of the oxygen evolution reaction (OER). Material properties of the catalysts are analyzed via Rutherford backscattering spectrometry, X-ray diffractometry, photoelectron spectroscopy, and Raman spectroscopy. Ta impurities are shown to be directly responsible for increasing the valence state of Ni sites and enhancing reaction kinetics, resulting in performance improvements of up to 64 mV at 10 mA cm–2 relative to pristine NiO. Particularly, we show that by applying operando Raman spectroscopy, Ta enhances the ability to create high-valence Ni in γ-NiOOH at a lower overpotential compared to the undoped sample. The lowered overpotentials of the OER can thus be attributed to the energetically less hindered advent of the creation of γ-NiOOH species on the pre-catalyst surface: a phenomenon otherwise unresolved through simple voltammetry.

Hetero-epitaxy growth of cobalt oxide/nickel oxide nanowire arrays on alumina substrates for enhanced ethanol sensing characteristics

In this work, Co3O4 nanowire arrays are prepared in-situ on the flat alumina substrates via a simple hetero-epitaxial growth without adding seed layers. It is found that the density of Co3O4 nanowires can be regulated by varying the concentration of NH4F that acts as substrate activation promoting the formation of nuclei on alumina substrate. In order to improve the gas-sensing performance, porous NiO nanosheets are anchored on the surface of Co3O4 nanowire arrays to form a novel heterostructure (Co3O4/NiO). Gas-sensing tests indicate a higher response value of these array composites towards ethanol (Rg/Ra = 4.26) than that of pristine Co3O4 nanowire arrays (Rg/Ra = 1.27) and NiO nanosheets (Rg/Ra = 1.89). The improved gas-sensing performances resulting from the special array structures and novel heterojunctions can provide abundant diffusion channels for gas molecules as well as a synergistic effect between Co3O4 and NiO.

Room-temperature processed hole-transport layer in flexible inverted perovskite solar cell module

Metal oxide-based electrodes are considered to have a key role in the future production of perovskite solar cells (PSCs). Here, we report a high-quality hole transport material deposited by solution-processed vanadium (V) substituted NiO nanomaterial at room-temperature, which holds better electrical conductivity and hole extraction ability as a reference sample. The smaller crystallite size of vanadium-substituted NiO than that of pristine NiO, decreased the surface roughness and significantly improved the surface wetting of the perovskite film. Therefore, vanadium-substitution improved the quality of the perovskite film. Furthermore, the presence of V5+ effectively enhanced the electrical conductivity of the NiO film as determined from the photovoltaic properties of the inverted PSC. The increase in electrical conductivity promoted charge transport and reduced interfacial charge accumulation. These enhanced performances and room-temperature deposition method validate the feasibility of the V-incorporated NiO for flexible PSC module with promising efficiency.

Nickel Cobaltite Nanoplate-Based Electrochemical Sensing Platform from Printable Inks for Simultaneous Detection of Dopamine and Uric Acid.

2D metal oxide-based nanomaterials have emerged as an exciting area of research owing to their rich electrochemical properties and diverse applications, including biosensors. In this work, we have synthesized ultra-thin Co3 O4 , NiO, and NiCo2 O4 nanostructures supported on a carbon cloth and printed graphite/Kapton substrates following thermal reduction of self-assembled metal alkanethiolates. These nanostructures act as a sensing platform for simultaneous detection of dopamine (DA) and uric acid (UA), important biological molecules in physiological and pathological tests. The ultrathin 2D nanoplates of NiCo2 O4 spinel formed in this study exhibit high electrochemical activity than pristine NiO and Co3 O4 . The electrochemical characterization studies indicate that NiCo2 O4 possesses a high potential for DA and UA with a peak separation of ∼140 mV, high sensitivity, and excellent selectivity. The low-cost and disposable, single-shot probe biosensors fabricated in this work possess a wide working range of 0.001-1000 μM with detection limits of 0.33 and 0.49 nM for DA and UA, respectively, with a practically achievable limit of quantification of ∼1 nM. Multiple sensing electrodes are printed on graphite/Kapton all at once following this method with improved reproducibility for DA and UA sensing further extending the scope of work towards mass fabrication and practical usage.

Synergistic effect of Cu-doped NiO for enhancing urea electrooxidation: Comparative electrochemical and DFT studies

In the present work, Cu-doped NiO is fabricated and synthesized using a microwave-assisted sol-gel method using different Ni and Cu precursors ratios supported on commercial graphite rod (G) and examined as an efficient electrocatalyst toward urea electrochemical oxidation (UEO). The morphology and chemical structure of the prepared electrocatalysts is confirmed by XRD, XPS, and SEM techniques. The catalytic activity of the prepared materials is measured and examined toward UEO as a function of current density and compared with different Ni-based catalysts in NaOH solution using cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy (EIS). The oxidation current density of G/Ni0.9Cu0.1 reached 32 mA cm-2, and its onset potential of urea oxidation peak is shifted from 0.43 V (vs. Ag/AgCl) in NiO catalyst to 0.40 V (vs. Ag/AgCl) for G/Ni0.9Cu0.1. The charge transfer resistance for different modified surfaces at various conditions (e.g., urea concentration, electrolyte concentration, and oxidation potential) is measured using the electrochemical impedance spectroscopy (EIS). The CO tolerance is studied using the DFT method to prove the stability of the electrodes and the performance efficiency due to Cu atoms dopping into NiO crystal. The adsorption of CO is studied upon Cu-doped NiO and compared with pristine NiO alloy at different adsorption sites- top and hallow.

NiO-TiO2 p-n Heterojunction for Solar Hydrogen Generation

Photocatalytic water splitting for hydrogen production has been widely recognized as a promising strategy for relieving the pressure from energy crisis and environmental pollution. However, current efficiency for photocatalytic hydrogen generation has been limited due to a low separation of photogenerated electrons and holes. p-n heterojunction with a built-in electric field emerges as an efficient strategy for photocatalyst design to boost hydrogen evolution activities due to a spontaneous charge separation. In this work, we investigated the effect of different preparation methods on photocatalytic hydrogen production over NiO-TiO2 composites. The results demonstrated that a uniform distribution of NiO on a surface of TiO2 with an intimate interfacial interaction was formed by a sol-gel method, while direct calcination tended to form aggregation of NiO, thus leading to an uneven p-n heterojunction structure within a photocatalyst. NiO-TiO2 composites fabricated by different methods showed enhanced hydrogen production (23.5 ± 1.2, 20.4 ± 1.0 and 8.8 ± 0.7 mmolh−1g−1 for S1-20%, S2-20% and S3-10%, respectively) as compared with pristine TiO2 (6.6 ± 0.7 mmolh−1g−1) and NiO (2.1 ± 0.2 mmolh−1g−1). The current work demonstrates a good example to improve photocatalytic hydrogen production by finely designing p-n heterojunction photocatalysts.

Assembly of In2O3 nanoparticles decorated NiO nanosheets heterostructures and their enhanced gas sensing characteristics

In this work, a series of In2O3/NiO composites with hierarchical structure were prepared through an efficient synthesis method based on electrospinning technique and ion exchange reaction. Material characterization confirmed that the composite was composed by one-dimensionally aligned NiO nanosheets with In2O3 nanoparticles evenly attached to them. Gas sensing properties of the In2O3/NiO series composites were systematically investigated, accompanying with pristine NiO sample for comparison. An obvious enhancement in ethanol sensing performance was discovered for the NiO based sensor via decoration with In2O3 nanoparticles. The gas sensing mechanism of In2O3/NiO composite towards ethanol based on the formation of nanoscale p-n heterojunction structure was discussed. Besides, gas response properties of the In2O3/NiO series sensors to some harmful gases (including ethanol, DMF, acetone and ammonia) were found out to be highly dependent on the component content within the composites. The different gas sensing patterns of In2O3/NiO series sensors could be utilized to discriminate among these target gases.

Effect of co-dopant proportion on the structural, optical and magnetic properties of pristine NiO nanoparticles synthesized by Sol–gel method

Effect of co-dopant proportion on the structural, optical and magnetic properties of pristine NiO nanoparticles synthesized by Sol–gel method

Effects on size, optical and antibacterial activity of pristine and Cr-doped NiO prepared by microwave-assisted method

In this work pristine and Cr-doped NiO were synthesized by microwave-assisted method. The products were characterized by X-ray diffraction (XRD), UV–vis absorption spectroscopy and photoluminescence (PL) spectroscopy. The significant feature of this manuscript is that the effects of pristine and Cr-doped NiO on the structural and optical properties of Cr-doped NiO were investigated for the first time. The average particle size of different samples was below 24 to13 nm. Pristine and Cr-doped NiO antibacterial activity is shown by all the prepared samples.

Synthesis of novel Co3O4 nanocubes-NiO octahedral hybrids for electrochemical energy storage supercapacitors

Fabrication of novel metal oxide nanostructured composites is a proficient approach to develop efficient energy storage devices and development of cost-free and eco-friendly metal oxide nanostructures for supercapacitor applications received considerable attention in recent years. The Co3O4 nanocubes-NiO octahedral structured composite was constructed using facile and one-step calcination process. Cyclic voltammetry, charge-discharge, and electrochemical impedance spectral techniques have been employed to analyze the specific capacitance of the synthesized nanostructures and the composites. Specific capacitance and cycling stability of the composites were evaluated with the pristine Co3O4 and NiO nanostructures. The composite showed a specific capacitance of 832 F g−1 at a current density of 0.25 A g−1, which was ~1.5 and ~1.9-times higher than pristine Co3O4 nanocubes and NiO octahedral structure, respectively. On the other hand, electrode showed approximately 50 % capacity retention at a higher current density (5 Ag-1) because of the uniform morphology of Co3O4 and NiO. The charge-discharge stability measurements of the composite showed an admirable specific capacitance retention capability, which was 94.5 % after 2000 continuous charge-discharge cycles at a current density of 5 A g−1. The superior electrochemical performance of the nano-composite was ascribed to synergistic effects and uniform morphology. Efficient nanostructure development using facile and one-step calcination process and electrochemical performance make the synthesized composite a promising device for supercapacitor applications.

Modification of TiO2 and NiO charge selective mesoporous layers using excessive Y and Li additions for carbon based perovskite solar cells

Carbon based perovskite solar cells are rapidly emerging as promising photovoltaic devices, combining low cost production and prolonged device operation, due to the exclusion of polymeric conductors and integration of highly durable metal oxide charge selective layers. Modification of metal oxide mesoporous layers via element additions and enhancement of electrical conductivity is a major strategy for reduced internal resistances inside the cell. This work investigates the effect of excessive Y and Li additions on the charge selective mesoporous layers. A novel flame synthesis method can be successfully employed for production of yttrium added TiO2 (Y:TiO2) and conductive lithium added NiO (Li:NiO) nanoparticles. This novel methanol combustion method is an effective strategy for incorporation of additives into host lattices, resulting in modified mesoporous layers. Ultraviolet photoelectron spectroscopy studies reveal a profound effect of Li and Y additions on the electronic band structure of the particles. Electrochemical impedance studies confirms that modification of TiO2 with excessive yttrium atoms results in suppressed charge injection, where excessive lithium addition enhances the charge transport properties of the NiO layer. Power conversion efficiency of the pristine NiO based cells are enhanced from 8.38% to 9.63% upon lithium addition, in a TiO2/MgO/Li:NiO/carbon configuration.

Introduction of surface defects in NiO with effective removal of adsorbed catalyst poisons for improved electrochemical urea oxidation

The electrochemical urea oxidation reaction (UOR) is a promising low cost method to replace water oxidation reaction for low energy electrochemical hydrogen production. The important factors to be considered in order to attain better UOR efficiency are electrocatalyst design by tuning defects and surface area and effective removal of CO2 poisoning on the catalyst surface. In this study, we have prepared surface oxidised NiO (e-NiO) with surface defects by electron beam bombardment and shown it to oxidize urea more effectively than pristine NiO with an onset potential of 0.33 V vs Ag/AgCl(sat.KCl) and Tafel slope of 34.69 mV/dec for 0.4 M urea in 1 M KOH electrolyte. The higher UOR current density exhibited by e-NiO is associated with the higher number of Ni3+ ions on the surface as revealed by X-ray photoelectron spectroscopy, leading to enhanced formation of NiO(OH) active species. A combination of voltammetry and impedance studies are presented to understand the active species formation and surface poisoning by released CO2 species. The dominant surface poisoning on e-NiO resulting from enhanced defects can be removed by increasing KOH concentration and the impedance spectra discloses effective removal of CO2 in 6 M KOH and 0.4 M urea. This is reflected in the UOR performance of e-NiO as drastic reduction in Tafel slope (22.29 mV/dec), lower onset potential (0.24 V vs Ag/AgCl(sat.KCl)) and high UOR current maxima of 20 mA/cm2 at the applied potential of 0.35 V vs Ag/AgCl(sat.KCl). The correlation of indirect and direct electrochemical urea oxidation reactions in pristine and e-NiO catalysts can be explained in terms of the strength of urea adsorption on surface sites derived from voltammograms and fitted impedance spectra.

Structure and reaction mechanism of binary Ni-Al oxides as materials for lithium-ion battery anodes.

A nanometer sized solid solution of NiO and Al2O3 was synthesized by calcination of Ni-Al layered double hydroxides (LDHs). The crystal structure of the obtained compound was determined by XRD and XAFS analyses: Ni2+ and Al3+ ions are located at the metal ion site of the rock salt structure and a certain amount of cation vacancies are also introduced for charge compensation. The electrochemical properties of the Ni-Al binary metal oxide as an anode material for lithium ion batteries were examined by the constant current charge-discharge test. Ni-Al oxide showed higher charging capacity in comparison with pristine NiO. In particular, the capacity in the lower voltage region (below 1.5 V), the limited capacity in this region is the weak point of the conversion anode, was improved to 540 mA h g-1 that is about twice that of pristine NiO. This improvement in the capacity in the lower voltage region is concluded to be due to the redox activity of Al3+ ions during the charge-discharge on the basis of the results of electrochemical measurements and ex situ XAFS measurements at the Ni and Al edge. The reaction mechanism of this compound is investigated using ex situ XRD and XAFS methods. For the charge (reduction) in the higher voltage region (OCV-1.0 V), lithium ion intercalation into the cation vacancy sites and/or lithium ion adsorption on the surface of particles are proceeding. For the charge in the lower voltage region (1.0-0.03 V), conversion reaction occurs by the reduction of Ni2+ and Al3+ ions to metal particles with surface electrolyte interface (SEI) layer formation. For the discharge in the lower voltage region (0.03-1.5 V), only Al metal particles are oxidized to Al3+ ions and some intermediate complexes are formed. For the discharge in the higher voltage region (1.5-3.0 V), the lattice of the Ni-Al binary oxide solid solution is reconstructed with the oxidation of Ni to Ni2+.

A universal electrochemical lithiation-delithiation method to prepare low-crystalline metal oxides for high-performance hybrid supercapacitors.

The electrochemical performance of transition metal oxides (TMOs) for hybrid supercapacitors has been optimized through various methods in previous reports. However, most previous research was mainly focused on well-crystalline TMOs. Herein, the electrochemical lithiation–delithiation method was performed to synthesise low-crystallinity TMOs for hybrid supercapacitors. It was found that the lithiation–delithiation process can significantly improve the electrochemical performance of “conversion-type” TMOs, such as CoO, NiO, etc. The as-prepared low-crystallinity CoO exhibits high specific capacitance of 2154.1 F g−1 (299.2 mA h g−1) at 0.8 A g−1, outstanding rate capacitance retention of 63.9% even at 22.4 A g−1 and excellent cycling stability with 90.5% retention even after 10 000 cycles. When assembled as hybrid supercapacitors using active carbon (AC) as the active material of the negative electrode, the devices show a high energy density of 50.9 W h kg−1 at 0.73 kW kg−1. Another low-crystallinity NiO prepared by the same method also possesses a much higher specific capacitance of 2317.6 F g−1 (302.6 mA h g−1) compared to that for pristine commercial NiO of 497.2 F g−1 at 1 A g−1. The improved energy storage performance of the low-crystallinity metal oxides can be ascribed to the disorder of as-prepared low-crystallinity metal oxides and interior 3D-connected channels originating from the lithiation–delithiation process. This method may open new opportunities for scalable and facile synthesis of low-crystallinity metal oxides for high-performance hybrid supercapacitors.

CuxNi1-xO nanostructures and their nanocomposites with reduced graphene oxide: Synthesis, characterization, and photocatalytic applications

NiO nanostructure was synthesized using a simple co-precipitation method and was embedded on reduced graphene oxide surface via ultrasonication. Structural investigations were made through X-ray diffraction (XRD) and functional groups were confirmed by Fourier transform infrared spectroscopy (FTIR). XRD analysis revealed the grain size reduction with doping. Fourier transform infrared spectroscopy confirmed the presence of metal-oxygen bond in pristine and doped NiO nanostructure as well as the presence of carbon containing groups. Scanning electron microscopy (SEM) indicated that the particle size decreased when NiO nanostructure was doped with copper. BET surface area was found to increase almost up to 43 m2/g for Cu doped NiO nanostructure/rGO composite. Current-voltage measurements were performed using two probe method. UV–Visible spectroscopic profiles showed the blue and red shift for Cu doped NiO nanostructure and Cu doped NiO Nanostructure/rGO composite respectively. Rate constant for Cu doped NiO nanostructure/rGO composite found to increase 4.4 times than pristine NiO nanostructure.