NiO Co3O4 Research Articles

Investigation of the Electrochemical Behavior of CuO-NiO-Co3O4 Nanocomposites for Enhanced Supercapacitor Applications.

In the present study, composites incorporating NiO-Co3O4 (NC) and CuO-NiO-Co3O4 (CNC) as active electrode materials were produced through the hydrothermal method and their performance was investigated systematically. The composition, formation, and nanocomposite structure of the fabricated material were characterized by XRD, FTIR, and UV-Vis. The FE-SEM analysis revealed the presence of rod and spherical mixed morphologies. The prepared NC and CNC samples were utilized as supercapacitor electrodes, demonstrating specific capacitances of 262 Fg-1 at a current density of 1 Ag-1. Interestingly, the CNC composite displayed a notable long-term cyclic stability 84.9%, which was observed even after 5000 charge-discharge cycles. The exceptional electrochemical properties observed can be accredited to the harmonious effects of copper oxide addition, the hollow structure, and various metal oxides. This approach holds promise for the development of supercapacitor electrodes. These findings collectively indicate that the hydrothermally synthesized NC and CNC nanocomposites exhibit potential as high-performance electrodes for supercapacitor applications.

Transition metal oxide-based NiO–Co3O4 nanocomposite as an electrode material for the high-performance supercapacitor

Transition metal oxide-based NiO–Co3O4 nanocomposite as an electrode material for the high-performance supercapacitor

Crystalline Structure and Optical Properties of Cobalt Nickel Oxide Thin Films Deposited with a Pulsed Hollow-Cathode Discharge in an Ar+O2 Gas Mixture

Cobalt nickel oxide films are deposited on Si(111) or fluorine-doped tin-oxide-coated (FTO) glass substrates employing a pulsed hollow-cathode discharge. The hollow cathode is operated with argon gas flowing through the nozzle and with O2 gas admitted to the vacuum chamber. Three different cathode compositions (Co20Ni80, Co50Ni50, and Co80Ni20) are investigated. Deposited and annealed thin films are characterized by X-ray diffraction, infrared (Raman) spectroscopy, and ellipsometry. As-deposited films consist of a single mixed cobalt nickel oxide phase. Upon annealing at 600 °C, the mixed cobalt nickel oxide phase separates into two cystalline sub-phases which consist of cubic NiO and cubic Co3O4. Annealed films are investigated by spectroscopic ellipsometry and the optical bandgaps are determined.

Bimetal-organic layer-derived ultrathin lateral heterojunction with continuous semi-coherent interfaces for boosting photocatalytic CO2 reduction

Current heterojunction photocatalysts suffer from sluggish charge transfer due to the discontinuous interfaces at an atomic level. Herein, we report a NiO–Co3O4 ultrathin lateral heterojunction using NiCo-based bimetal–organic layers as precursors. The atomic-resolution images display a unique continuous semi-coherent interface between NiO and Co3O4. The experimental results confirm that the continuous semi-coherent interfaces effectively expedite the electron transfer from NiO to Co3O4. Concomitantly, the electron transfer raises d-band center of Co3O4 in NiO–Co3O4 toward Fermi level, as revealed by the density functional theory calculations. As a result, the *COOH intermediate can be strongly bound on cobalt reactive centers. The successful modulation of charge transfer and intermediate binding by continuous semi-coherent interfaces leads to a remarkable gas yield of 22.67 mmol h−1 from photocatalytic CO2 reduction over NiO–Co3O4. This work highlights the crucial roles of interface engineering in regulating carrier kinetics and surface reactions.

The photocatalytic hydrogen evolution and photoreduction CO2 selective enhancement of Co3O4/Ti3+-TiO2/NiO hollow core-shell dual pn junction

The potential and threshold would be the most important issues for photocatalysis, including hydrogen evolution reaction (HER) and CO2 selective photoreduction. The Co3O4/Ti3+-TiO2/NiO hollow core-shell heterojunction is fabricated via a continuous chemical-hydrothermal-annealing-reduction method. As demonstrated, the as-prepared Co3O4/Ti3+-TiO2/NiO hollow core-shell heterojunction exhibits remarkable photocatalytic performance enhancement than single TiO2, including H2 evolution (∼2134.63 μmol/g∙h, ∼80 folds) and CO2 photoreduction (H2/CH4/CO: ∼34.85/132.25/12.65 μmol/g∙h, ∼30 folds), and achieves enhanced CO2 photoreduction selectivity, which can be mainly ascribed to the synergism of Ti3+/Ov and dual pn junction. There, the Ti3+/Ov can not only increase the solar efficiency, but also decrease the threshold of H2O*→H* and *CO→*CHO to enhance HER and CH4 selectivity, including promote H+ diffusion and H2O/CO2/*CO absorption. All these can be supported by the density functional theory (DFT) calculation. Additionally, the formed Co3O4/Ti3+-TiO2/NiO dual pn junction can promote the photo-generated carrier separation/transport efficiently. Furthermore, the hollow core-shell structure obtained by Cobalt 2-methylimidazole (ZIF-67) self-template can increase solar efficiency, and the NiO nanosheets and Co3O4 nanoparticles can increase active sites.

NiO–Co3O4–rGO as a Multicomponent Transition Metal Oxide Nanocatalyst for Ultra‐level Detection of Nitrite in Beef and Tap Water Samples

AbstractThe detection of nitrite as a challenging compound in food industries has always been a necessity. To this purpose, herein, two transition metal oxide‐based nanocatalysts, NiO–Co3O4 (NC) and its reduced graphene hybridized form, NiO–Co3O4–rGO (NCR), are synthesized by a hydrothermal method and characterized by X‐ray diffraction, Raman spectroscopy, scanning electron microscope (SEM) images, and energy dispersive X‐ray analysis (EDAX) mapping. The synthesized materials are exploited to modify a glassy carbon electrode and fabricate an effective sensor for nitrite detection in real samples through differential pulse voltammetry (DPV). NCR shows excellent sensitivity (40.44 µA per dec), very low limit of detection (20 × 10‐9 m), significant accuracy, and good stability at the wide range of nitrite ions (100–500 × 10‐9 m) in real samples.

Improved proton conductivity in MoS2–NiO–Co3O4 filled chitosan based proton exchange membranes for fuel cell applications

Proton exchange membrane (PEM) is an essential component of the membrane electrode assembly in the polymer electrolyte fuel cells (PEFC) which should display efficient proton conduction for better performance. Chitosan (CS) based PEMs are proposed as proton conductors for PEFCs for their film-forming and biodegradable nature to replace the synthetic, hydrocarbon-derived PEMs. However, the crystalline nature as well as poor reinforcement of the saccharide backbone lowers the proton conductivity of CS, and this prevents its commercialization as state-of-the-art PEM for fuel cell applications. Here, we report a CS based nanocomposite membranes which delivers a maximum proton conductivity of 44.45 mS cm−1 at 80 °C under partially hydrated conditions. Exfoliated MoS2 nanosheets and magnetically active NiO–Co3O4 are introduced as active fillers in the CS matrix to improve the proton conductivity and stability of the prepared membranes. The fabricated CS nanocomposite membranes are also investigated for their mechanical characteristics, degree of swelling, water-retention and ion-exchange properties. The obtained results suggest the utility of these membranes as alternative PEMs for fuel cell applications.

Synthesis of Rod-like NiO–Co3O4 Composites for Sensitive Electrochemical Detection of Hydrogen Peroxide

Synthesis of Rod-like NiO–Co3O4 Composites for Sensitive Electrochemical Detection of Hydrogen Peroxide

Design of Hierarchical NiCo2O4 Nanocages with Excellent Electrocatalytic Dynamic for Enhanced Methanol Oxidation.

Although sheet-like materials have good electrochemical properties, they still suffer from agglomeration problems during the electrocatalytic process. Integrating two-dimensional building blocks into a hollow cage-like structure is considered as an effective way to prevent agglomeration. In this work, the hierarchical NiCo2O4 nanocages were successfully synthesized via coordinated etching and precipitation method combined with a post-annealing process. The nanocages are constructed through the interaction of two-dimensional NiCo2O4 nanosheets, forming a three-dimensional hollow hierarchical architecture. The three-dimensional supporting cavity effectively prevents the aggregation of NiCo2O4 nanosheets and the hollow porous feature provides amounts of channels for mass transport and electron transfer. As an electrocatalytic electrode for methanol, the NiCo2O4 nanocages-modified glassy carbon electrode exhibits a lower overpotential of 0.29 V than those of NiO nanocages (0.38 V) and Co3O4 nanocages (0.34 V) modified glassy carbon electrodes. The low overpotential is attributed to the prominent electrocatalytic dynamic issued from the three-dimensional hollow porous architecture and two-dimensional hierarchical feature of NiCo2O4 building blocks. Furthermore, the hollow porous structure provides sufficient interspace for accommodation of structural strain and volume change, leading to improved cycling stability. The NiCo2O4 nanocages-modified glassy carbon electrode still maintains 80% of its original value after 1000 consecutive cycles. The results demonstrate that the NiCo2O4 nanocages could have potential applications in the field of direct methanol fuel cells due to the synergy between two-dimensional hierarchical feature and three-dimensional hollow structure.

Atomic Layer Deposition of NiO on Self‐Supported Co3O4 Nanoneedle Array for Electrocatalytic Methanol Oxidation Reaction

Developing efficient transition metal oxide catalysts is still challenging for direct methanol fuel cells. Herein, an atomic layer deposition method to prepare NiO on a self‐supported Co3O4 nanoneedle array grown on a porous nickel foam substrate (NiO–Co3O4 NA@NF) as the electrode for the methanol oxidation reaction (MOR) is reported. The synergistic effect between the NiO and Co3O4 components as well as the specific 3D nanoarray structure can endow the prepared NiO–Co3O4 NA@NF with a very promising MOR catalytic activity. As a result, the NiO–Co3O4 NA@NF catalyst shows a low onset potential (1.27 V vs reversible hydrogen electrode [RHE]), a high current density (173 mA cm−2@1.524 V vs RHE), and good stability in MOR. This work demonstrates the feasibility of the atomic layer deposition strategy in fabricating complex oxides‐based high‐performance electrocatalysts.

Facile synthesis and characterization of conducting polymer-metal oxide based core-shell PANI-Pr2O–NiO–Co3O4 nanocomposite: As electrode material for supercapacitor

Metal oxide nanoparticles and their composites with conducting polymers, specifically Polyaniline (PANI) were utilized for fabricating nanoscale supercapacitor (SC) electrode materials. In the present study, we have synthesized pristine Pr2O3, NiO, Co3O4 nanoparticles, binary PANI-Pr2O3, PANI-NiO, PANI-Co3O4, ternary Pr2O3–NiO–Co3O4, and quaternary PANI-Pr2O3–NiO–Co3O4 spherical core-shell nanocomposite using co-precipitation and ultra-sonication methods. The grown samples were characterized with different analytical techniques. The XRD pattern revealed that the as-synthesized products were crystalline with Pr2O3 hexagonal phase, NiO cubic phase, and Co3O4 cubic phase in pure and nanocomposites. The Williamson-Hall, Scherrer, and size-strain plot methods were employed to study the crystalline development and contribution of micro-strain. FTIR pattern exhibited the metal-oxygen and PANI bond vibrations. FE-SEM images shown the spherical core-shell shape morphology of quaternary nanocomposite. EDX evident the presence of praseodymium, cobalt, and nickel in synthesized samples. UV–vis spectroscopy confirmed the absorption in the visible region. The IV graphs showed a higher conductivity of quaternary nanocomposite. The cyclic voltammetry results revealed that the quaternary nanocomposite has a higher specific capacitance 500 Fg-1 as compared to binary nanocomposites 134 F g−1 (PANI-Pr2O3), 143 F g−1 (PANI-Co3O4), 256 F g−1 (PANI-NiO), and PANI (90.8 F g−1) at a scan rate of 5 m Vs−1. The GCD results also showed that the quaternary nanocomposite has a higher specific capacitance of 905 F g−1 at current density 1 A g−1 with maximum energy density and power density of 87.99 kWhkg-1 and 2.6 k W kg−1, respectively. The EIS curve also confirmed that the quaternary nanocomposite has a lower polarization resistance (Rp) and solution resistance (Rs). The higher capacitance of quaternary nanocomposite can facilitate ion transfer, and the formation of its core-shell structure flourish to enhance surface-dependent electrochemical properties. Furthermore, this study gives a novel research idea to manufacture electrode materials for supercapacitors.

Effect of Ni/Co mass ratio and NiO-Co3O4 loading on catalytic performance of NiO-Co3O4/Nb2O5-TiO2 for direct synthesis of 2-propylheptanol from n-valeraldehyde.

In the direct synthesis of 2-propylheptanol (2-PH) from n-valeraldehyde, a second-metal oxide component Co3O4 was introduced into NiO/Nb2O5–TiO2 catalyst to assist in the reduction of NiO. In order to optimize the catalytic performance of NiO–Co3O4/Nb2O5–TiO2 catalyst, the effects of the Ni/Co mass ratio and NiO–Co3O4 loading were investigated. A series of NiO–Co3O4/Nb2O5–TiO2 catalysts with different Ni/Co mass ratios were prepared by the co-precipitation method and their catalytic performances were evaluated. The result showed that NiO–Co3O4/Nb2O5–TiO2 with a Ni/Co mass ratio of 8/3 demonstrated the best catalytic performance because the number of d-band holes in this catalyst was nearly equal to the number of electrons transferred in hydrogenation reaction. Subsequently, the NiO–Co3O4/Nb2O5–TiO2 catalysts with different Ni/Co mass ratios were characterized by XRD and XPS and the results indicated that both an interaction of Ni with Co and formation of a Ni–Co alloy were the main reasons for the reduction of NiO–Co3O4/Nb2O5–TiO2 catalyst in the reaction process. A higher NiO–Co3O4 loading could increase the catalytic activity but too high a loading resulted in incomplete reduction of NiO–Co3O4 in the reaction process. Thus the NiO–Co3O4/Nb2O5–TiO2 catalyst with a Ni/Co mass ratio of 8/3 and a NiO–Co3O4 loading of 14 wt% showed the best catalytic performance; a 2-PH selectivity of 80.4% was achieved with complete conversion of n-valeraldehyde. Furthermore, the NiO–Co3O4/Nb2O5–TiO2 catalyst showed good stability. This was ascribed to the interaction of Ni with Co, the formation of the Ni–Co alloy and further reservation of both in the process of reuse.

Surface engineered NiO–Co3O4 nanostructures as high-performance electrocatalysts for oxygen reduction reaction

The development of low-cost and high-performance oxygen reduction reaction (ORR) catalysts is important for renewable energy storage and conversion systems, such as fuel cell. Herein, we report a simple and facile surface engineering strategy for nickel and cobalt based (NiO–Co3O4) hybrid as efficient and robust ORR electrocatalyst. The surface nanostructure of NiO–Co3O4 nanohybrids can be easily tuned by controlling the precursor amounts of nickel and cobalt during a wet-chemical synthesis. With an optimal composition, an intriguing surface structure consisted of one dimensional (1D) nanorod with two dimensional (2D) nanosheet can be obtained for NiO–Co3O4 nanohybrids, which significantly boosts ORR electrocatalytic activity as well as stability. A facile charge or mass transfer within 1D and 2D open surface nanostructures is mainly responsible for an excellent catalytic performance of NiO–Co3O4 nanohybrids.

NiO@NiO and NiO@Co³O⁴ Hollow Core/Shell Composites for High-Performance Supercapacitor Electrodes.

In the present work, NiO@NiO and NiO@Co³O⁴ core/shell composites have been fabricated by a facile hydrothermal process and investigated as electrodes for supercapacitors. The structure and the morphology of as-prepared samples 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 NiO nanosheets and Co³O⁴ nanowires. Electrochemical properties were evaluated by cyclic voltammetry, galvanostatic charge/discharge measurements, and electrochemical impedance spectroscopy. According to the results NiO@NiO and NiO@Co³O⁴ core/shell composites exhibited high specific capacitance, being promising for high-performance supercapacitors.

Pseudocapacitive Charge Storage in Thin Nanobelts

This article reports that extremely thin nanobelts (thickness ~ 10 nm) exhibit pseudocapacitive (PC) charge storage in the asymmetric supercapacitor (ASC) configuration, while show battery-type charge storage in their single electrodes. Two types of nanobelts, viz. NiO–Co3O4 hybrid and spinal-type NiCo2O4, developed by electrospinning technique are used in this work. The charge storage behaviour of the nanobelts is benchmarked against their binary metal oxide nanowires, i.e., NiO and Co3O4, as well as a hybrid of similar chemistry, CuO–Co3O4. The nanobelts have thickness of ~ 10 nm and width ~ 200 nm, whereas the nanowires have diameter of ~ 100 nm. Clear differences in charge storage behaviours are observed in NiO–Co3O4 hybrid nanobelts based ASCs compared to those fabricated using the other materials—the former showed capacitive behaviour whereas the others revealed battery-type discharge behaviour. Origin of pseudocapacitance in nanobelts based ASCs is shown to arise from their nanobelts morphology with thickness less than typical electron diffusion lengths (~ 20 nm). Among all the five type of devices fabricated, the NiO–Co3O4 hybrid ASCs exhibited the highest specific energy, specific power and cycling stability.

Synthesis of NiO–Co3O4 nanosheet and its temperature-dependent supercapacitive behavior

A nanosheet of nickel and cobalt double hydroxides (NC RT) has been synthesized by the facile hydrothermal method. It has been treated at temperatures of 300 °C, 400 °C and 500 °C, namely NC 300, NC 400 and NC 500, respectively, to obtain a nanosheet of NiO–Co3O4. Samples have been investigated using XRD, Raman spectroscopy, FESEM and TEM. It can be observed that nickel hydroxide is converted to NiO at 300 °C, whereas cobalt hydroxide is converted to Co3O4 at 400 °C. The double hydroxide nanosheet leads to porous oxide nanosheet at an elevated temperature. The formation of porous structure could be attributed to the rapid release of water molecules during thermal treatment. Four symmetric supercapacitors are prepared with NC RT, NC 300, NC 400 and NC 500 as electrode materials, keeping 3 M KOH as an electrolyte and Whatman filter paper as a separator for all the symmetric supercapacitors. It can be seen that the specific capacitances of the NC RT, NC 300, NC 400 and NC 500 symmetric supercapacitors are decreased with increasing temperature in the range of 25 °C–80 °C and scan rate in the range of 10–500 mV s−1. It can be seen that the NC 300 has excellent supercapacitive behavior. The specific capacitance of NC RT decreased from 20 to 6 F g−1, NC 300 decreased from 324 to 57 F g−1, NC 400 decreased from 132 to 61 F g−1 and NC 500 decreased from 81 to 48 F g−1 with the variation of scan rate from 10–500 mV s−1. The decrement in the specific capacitance may be attributed to the increased bulk and charge transfer resistance at elevated temperature.

High-Valence-State NiO/Co3O4 Nanoparticles on Nitrogen-Doped Carbon for Oxygen Evolution at Low Overpotential

The electrocatalytic oxygen evolution reaction (OER) plays a critical role in sustainable energy conversion and storage, but OER is severely hampered owing to the lack of highly efficient catalysts. Here, we report an efficient electrocatalyst, with NiO/Co3O4 nanoparticles decorated on nitrogen-doped carbon (NiO/Co3O4@NC). Abundant high-valence Ni3+ and Co3+ species were observed on the surface of the hybrid due to the strong NC–metal oxide and NiO–Co3O4 interactions. This unique structure leads to excellent OER performance, delivering a very low overpotential of 240 mV@10 mA·cm–2 on glassy carbon and 200 mV@10 mA·cm–2 on Ni foam in KOH and having a turnover frequency (@350 mV overpotential) 6 and 16 times higher than that of IrO2 and RuO2, respectively.

Design and synthesis of ZnO–NiO–Co3O4 hybrid nanoflakes as high-performance anode materials for Li-ion batteries

ZnO–NiO–Co3O4 hybrid nanoflakes are fabricated via a simple hydrothermal method followed by a subsequent annealing process.

Enhancement of Low-field Magnetoresistance in Self-Assembled Epitaxial La0.67Ca0.33MnO3:NiO and La0.67Ca0.33MnO3:Co3O4 Composite Films via Polymer-Assisted Deposition.

Polymer-assisted deposition method has been used to fabricate self-assembled epitaxial La0.67Ca0.33MnO3:NiO and La0.67Ca0.33MnO3:Co3O4 films on LaAlO3 substrates. Compared to pulsed-laser deposition method, polymer-assisted deposition provides a simpler and lower-cost approach to self-assembled composite films with enhanced low-field magnetoresistance effect. After the addition of NiO or Co3O4, triangular NiO and tetrahedral Co3O4 nanoparticles remain on the surface of La0.67Ca0.33MnO3 films. This results in a dramatic increase in resistivity of the films from 0.0061 Ω•cm to 0.59 Ω•cm and 1.07 Ω•cm, and a decrease in metal-insulator transition temperature from 270 K to 180 K and 172 K by the addition of 10%-NiO and 10%-Co3O4, respectively. Accordingly, the maximum absolute magnetoresistance value is improved from −44.6% to −59.1% and −52.7% by the addition of 10%-NiO and 10%-Co3O4, respectively. The enhanced low-field magnetoresistance property is ascribed to the introduced insulating phase at the grain boundaries. The magnetism is found to be more suppressed for the La0.67Ca0.33MnO3:Co3O4 composite films than the La0.67Ca0.33MnO3:NiO films, which can be attributed to the antiferromagnetic properties of the Co3O4 phase. The solution-processed composite films show enhanced low-field magnetoresistance effect which are crucial in practical applications. We expect our polymer-assisted deposited films paving the pathway in the field of hole-doped perovskites with their intrinsic colossal magnetoresistance.

Preparation, ferromagnetic and photocatalytic performance of NiO and hollow Co3O4 fibers through centrifugal-spinning technique

Both NiO and hollow Co3O4 fibers with the diameter of about 10μm have been successfully prepared through spinning high viscous sols into precursor fibers and followed calcination process. The evolution process from precursor to crystalline fibers and the microstructures of the obtained fibers were characterized by TG-DSC, FT-IR, XRD, HRTEM, SEM and the like. The method is facile and cost-effective for mass production of fibers and the obtained fibers are pure phase with high crystallinity. Their magnetic properties were investigated, showing that both the fibers are ferromagnetic. Meanwhile, the NiO fibers exhibit good photocatalytic performance for the removal of Congo red from water under UV light irradiation.