NiCo2O4 Materials Research Articles

Separation of valuable metals from low nickel matte to prepare NiCo2O4 materials: Optimization of oxidative leaching process and improvement of electrochemical properties of materials

The economical and efficient utilization of intermediate low nickel matte has become an important goal of nickel smelting industry. In this work, an innovative process of oxidative leaching of valuable metal from low nickel matte to prepare NiCo2O4 materials was proposed based on the materials utilization of mineral. The addition method and speed of ammonium persulfate in the oxidative leaching process was investigated to improve the extraction of valuable metals. The key factors affecting the leaching of valuable metals and the optimum leaching condition were determined by orthogonal experiments, and the extraction of Ni, Cu, and Co was 92.3 %, 97.1 % and 96.6 %, respectively. The leaching mechanism was clarified and the advantages of the leaching process were compared and analyzed. The kinetics of oxidative leaching process was studied by timing sampling method, and the control model, activation energy and kinetic equation of Ni, Cu and Co leaching were determined by analyzing the data with unreactive shrinkage model. The effects of Ni:Co ratio and calcination temperature of precursor on the properties of NiCo2O4 were investigated using the leaching solution removing iron and copper as raw materials. The NiCo2O4 material with the Ni:Co ratio of 1:2 prepared by calcining precursor at 750 ℃ for 3 h has a specific capacitance of 864F/g when the current density is 1 A/g. The prepared NiCo2O4 materials show good capacitance performance and has potential to be used as capacitor electrodes. This work combines metal extraction with product materialization, which is expected to help the metallurgical industry effectively shorten the industrial production process and reduce production costs.

One-step synthesis of double-walled NiCo2O4 hollow nanotubes using hollow fiber templates created by airflow-coaxial electrospinning

Metal oxide electrode material NiCo2O4 has significant potential for application as an Electrode material due to its excellent electrochemical performance and environmentally friendly characteristics. This paper utilizes a unique airflow-coaxial electrospinning technique combined with a simple one-step solution reaction to prepare NiCo2O4 nanotubes with a complex double-walled hollow structure. The XPS and XRD results demonstrated the synthesis of the NiCo2O4 materials, while the SEM and TEM results verified the presence of a double-walled hollow structure in the NiCo2O4 nanotubes. The electrochemical performance of the NiCo2O4 double-walled hollow nanotubes is significantly improved compared to those single-layer hollow nanotubes. The maximum specific capacitance of those two kinds of nanotubes is 437.5 F/g and 336.7 F/g under the current density of 1 A/g, respectively. The origin of the electrochemical performance improvement can be attributed to the increased specific surface area and the presence of interlayer ion transport channels in the double-walled hollow structure. The study is very helpful in improving the application prospect of NiCo2O4 material as the electrode material of supercapacitors. Equally important, this study also presents an efficient method to fabricate double-walled hollow nanostructures based on special templates.

Carbon-modified NiCo2O4 as an electrode material for supercapacitors

Transition metal oxides are a promising class of electrode materials for pseudocapacitors due to their high electrochemical activity and eco-friendly nature. However, they possess poor intrinsic conductivity which results in the low energy density of the assembled supercapacitors. In this study, electrodes composed of amorphous C-modified NiCo2O4 (C/NiCo2O4/NF) on nickel foam substrate were prepared by electrochemical deposition and thermostatic heating method. The incorporation of amorphous C compensates for the low electrical conductivity of NiCo2O4 materials, thereby significantly enhancing the electrochemical performance. The galvanostatic charge-discharge (GCD) test results reveal an impressive specific capacitance of 379.4 mF/cm2 at a current density of 1.5 mA/cm2, and with a capacitance retention rate of 87.1 %. In addition, the symmetric supercapacitor assembled using C/NiCo2O4 electrode materials exhibits exceptional energy density and power density, reaching maximum values of 522.3 μWh/cm2 and 900 μW/cm2 respectively. The device is capable of illuminating LED for up to 8 min, further demonstrating its practical applicability. These results underscore the feasibility and promise of C/NiCo2O4 as an electrode material for the advancement of high-performance supercapacitors.

Electronic and structural disorder of NiCo2O4 nanostructures using phytochemicals from desert gourd offered efficient asymmetric supercapacitor and oxygen evolution reaction

In this study, we have utilized the raw material of desert gourd fruit juice which distributed in the wide range of desert areas of the world. The desert gourd juice carries a significant content of acidic compounds which can slightly decrease the pH of growth solution, hence it could impart a significant role in the morphological transformation. Also, the purpose of using desert gourd fruit juice was the availability of rich amount of green reducing, capping and stabilizing agents for obtaining the short range and closely packed nanoparticles of NiCo2O4. The preparation of nanostructured NiCo2O4 materials was carried out by using desert gourd fruit juice through hydrothermal process followed by thermal annealing in air. The morphology, crystalline structure, surface chemical composition and localized atomic investigations were performed by several analytical techniques. The role of desert gourd fruit juice on the structural and functional features of NiCo2O4 was also explored. The desert gourd juice through the decrease in the pH of growth solution and carrying green reducing, capping and stabilizing agents originating closely packed NiCo2O4 nanoparticles instead of nanorod like morphology. The oxygen evolution reaction (OER) half-cell characterization demonstrated overpotential of 260 mV@10 mAcm−2, Tafel slope of 62 mV dec−1 and durability of 40 h using NiCo2O4 nanostructures prepared with 2 mL of desert gourd juice. Moreover, energy storage aspects of NiCo2O4 nanostructures prepared with desert gourd juice were studied for supercapacitor application and an asymmetric supercapacitor (ASC) was developed. The findings of presented study revealed a high specific capacitance (Cs) 1958.17 F/g for newly developed ASC and high retention percentage of 99–90 % during cycling stability was also notice. The enhanced performance of as prepared NiCo2O4 nanostructures are attributed from the formation of unique architecture, surface oxygen vacancies, high ionic diffusion, high exposure of surface active sites, fast electron communication, swift charge transport at the interface between electrode and electrolyte.

Promoted electrocatalytic water splitting by regulating the concentration of oxygen vacancies

Among the many methods of hydrogen production, the electrolysis of water has a broad prospect. In this experiment, NiCo2O4 nanosheets with different degrees of oxidation were synthesized on nickel foam by the hydrothermal method, air calcination and reduction steps. The experimental results show that reduction treatment significantly improved the catalytic activity of NiCo2O4 materials under alkaline medium conditions of 1.0 mol/L KOH. V–NiCo2O4-4 shows better catalytic activity with an overpotential of 285 mV and 340 mV for the oxygen evolution reaction (OER) at 10 mA cm−2 and 50 mA cm−2, respectively. The better catalytic activity of V–NiCo2O4-4 is mainly assigned to the flower-like structure of the catalyst surface and the moderate reduction of NaBH4, resulting in more oxygen vacancies and active sites. Density functional theory calculation also indicates that the V–NiCo2O4-4 material has a stronger water absorption energy (0.75 eV) compared to the V–NiCo2O4-2 and V–NiCo2O4-6 materials, which provides a new foundation for the construction of binder-free high-performance electrodes for water splitting.

A novel template processing method for preparing spinel oxides with various morphologies to assemble high-performance supercapacitors

With the increasing complexity of the application scenarios of nanomaterials, transition metal oxides (TMOs) have shown excellent development potential. However, the synthesis of TMOs with customized morphologies for different application environments is still challenging. Herein, an acid-alcohol treatment based on the different intensities of the redox reactions between nitric acid and ethanol was developed to prepare different carbon templates. Through impregnation and annealing of the templates, NiCo2O4 (NCO) materials with hollow spherical (NCO-HS), multi-shell spherical (NCO-MS), and lamellar (NCO-L) morphologies were obtained. The characterization was performed through different analytical methods, which revealed various structures, morphologies, and surface chemistry of the materials. NCO-HS, NCO-MS, and NCO-L were tested for supercapacitor applications and exhibited a high specific capacitance of 402.6, 1037.1, and 531.4 F g−1, respectively. Overall, the proposed method can be used to customize the synthesis of functional materials with various morphologies for future advanced applications.

Construction of NiCo2O4@CNPs core-shell nanocomposites with 2D leaf-like structure for high-performance supercapacitor

Exploitation of NiCo2O4-based novel composite electrode materials with enhanced comprehensive properties is essential for high-performance supercapacitors. Herein, ultrathin NiCo2O4 nanosheets wrapped carbon nanoplates (NiCo2O4@CNPs) are fabricated by co-precipitation method and subsequent thermal annealing treatment. Characterization results indicate that 2D leaf-like NiCo2O4@CNPs is synthesized and NiCo2O4 nanosheets with thickness of 4 nm are tightly wrapped on CNPs. The NiCo2O4@CNPs is possessed of enhanced electrochemical properties in comparison to bare CNPs, bare NiCo2O4 and other NiCo2O4-based materials reported in literatures. The NiCo2O4@CNPs electrode shows higher specific capacitance (1265 F g−1 at 1 A g−1) and remarkable rate capability. Furthermore, the NiCo2O4@CNPs electrode has excellent cycling stability, and 97.3% of the initial specific capacitance still remains after 2000 cycles. Reasons for the enhanced electrochemical properties of NiCo2O4@CNPs were analyzed. In addition, the supercapacitor of NiCo2O4@CNPs//NiCo2O4@CNPs displays a high energy density of 32.4 Wh kg−1 at 435 W kg−1 and a high power density of 8676 W kg−1 at 14.4 Wh kg−1. The above results manifested that NiCo2O4@CNPs is an potential electrode material for fabricating high-performance supercapacitor.

Magnetic urchin‐like NiCo2O4 material derived from wastes as a peroxymonosulfate activator for the degradation of bisphenol A

AbstractIn this study, the magnetic urchin‐like NiCo2O4 materials (NiCo2O4‐w) were successfully prepared from the waste during the preparation of NiCo2O4/carbon cloth composite, and further evaluated as a peroxymonosulfate activator for removing bisphenol A (BPA). The effect of various factors such as initial solution pH, peroxymonosulfate (PMS) concentration, catalyst concentration, and coexisting ions on the BPA removal were evaluated. The optimal factors were 0.20 g L−1 catalyst, 0.10 g L−1 PMS, 7.14 pH (unadjusted). Moreover, the NiCo2O4‐w exhibited good catalytic effects over wide ranges of pH (3.73 to 12). SO42− and H2PO4− remarkably inhibited the BPA removal, NO3− obviously inhibited the BPA removal, while Cl− and HCO3− had a little effect on the BPA removal. Singlet oxygen (1O2), superoxide radical (O2•−), hydroxyl radical (•OH) and sulfate radical (SO4•−) participated in the BPA degradation, of which O2•− and 1O2 played the leading role, especially O2•−. Oxygen vacancies, redox cycling pairs of Co(III)/Co(II) and Ni(III)/Ni(II) were responsible for PMS activation. Moreover, the degradation routes of BPA were rationally put forward. This present work not only presents that NiCo2O4‐w has a low‐cost, magnetically recoverable catalyst for high efficient degradation of wastewater containing BPA, but also opens up a new avenues to reduce environmental problems associated with waste treatment during the preparation of heterogeneous catalyst.

Preparation and properties of nickel site doped material Ni1-yXyCo2O4 as supercapacitor materials by in-situ growth method

Although NiCo2O4 has been widely applied in supercapacitors, its actual capacity has been limited by the low conductivity and reactivity. Due to the relationship between the performance of the spinel-structured NiCo2O4 electrode material and its microstructure, in this paper, in order to modify the nanostructure of NiCo2O4 to improve its electrochemical performance, hydrothermal method is adopted to synthesize Ni0.98X0.02Co2O4(X = Fe, Cu, Mg, V, Ag, Mn, Mo, Ti) grown on nickel foam. After the synthesis, the physical morphology of the selected Ni0.98Mg0.02Co2O4 and Ni0.98Mn0.02Co2O4 are tested and analyzed by XRD, SEM, XPS and FT-IR. According to the characterization results, it can be found that different kinds of metals are doped in the nickel site of NiCo2O4, and the microscopic morphology of materials is different. It can be seen from the SEM figure that Ni0.98Mg0.02Co2O4 is a small nano-scale particle, while Ni0.98Mn0.02Co2O4 presents rod-like braided structure, and doping at the nickel site does not affect the main structure of the material. It can be seen from EDS data that the atomic ratio and weight ratio of nickel and cobalt elements are consistent with the molecular formula. The XPS spectra of the corresponding elements showed that Ni, Co and O elements were corresponding to NiCo2O4 materials. In conclusion, the result of physical morphology characterization analysis shows that the material is still in standard NiCo2O4 spinel structure.

High-performance hybrid supercapacitor with electrochemically exfoliated graphene oxide incorporated NiCo2O4 in aqueous and non-aqueous electrolytes

Hydrothermal approach is employed to synthesize electrochemically exfoliated graphene oxide (EGO) integrated NiCo2O4 micro-flowers with nano petals. Specific capacity of 59 mAh g−1 (530 F g−1) is achieved by the optimized weight percentage of EGO in NiCo2O4 with long cyclic stability over 10,000 cycles. Detailed analysis on charge-storage properties of NiCo2O4–EGO composite reveals individual capacitive and diffusive contributions at various scan rates. An asymmetric supercapacitor device is fabricated with EGO incorporated NiCo2O4 composite material and commercial YP-50F carbon as positive and negative electrodes in 1 M TEABF4 acetonitrile organic electrolyte for the first time. The device delivers promising electrochemical performance with energy and power densities of 37.8 Wh kg−1 and 1350 W kg−1. Present work suggests an eco-friendly synthesis of EGO and provides a cost-effective facile approach for improving the overall electronic conductivity and cyclic stability of NiCo2O4 and other similar metal oxide materials for high-performance supercapacitors.

Facile Cetyl Trimethyl Ammonium Bromide-assisted Hydrothermal Synthesis of Spinel NiCo2O4 Nanoplates as an Electrode Material for Supercapacitor Application

Ternary NiCo2O4 has paying more attention as a class of potential electrochemical energy storage materials. In the present endeavor, we report spinel NiCo2O4 nanoplates, which were prepared by cetyl trimethyl ammonium bromide (CTAB)-assisted hydrothermal technique followed by proper calcination process. The structural and morphological features were characterized by x-ray diffraction, Fourier transform infrared spectra, scanning electron microscope and high-resolution transmission electron microscopic analyses. The supercapacitive properties of the materials were evaluated using cyclic voltammetric, electrochemical impedance spectroscopy and galvanostatic charge/discharge analysis in 1 M NaOH electrolyte. The freshly prepared NiCo2O4 materials offer the specific capacitance of 329 mA h g−1 at a current density of 1 A g−1, and it provides superior long-term cyclic stability, which retained 97% of initial capacitance after 2000 continuous CV cycles at a high scan rate of 100 mV s−1. These outcomes demonstrate thus prepared spinel NiCo2O4 as a significant electrode material for supercapacitor application.

Multicomponent hierarchical NiCo2O4@CoMoO4@Co3O4 arrayed structures for high areal energy density aqueous NiCo//Zn batteries

Directly growing nickel/cobalt-based cathode materials on current collectors as binder-free electrodes for rechargeable aqueous nickel/cobalt-Zn-based (NiCo//Zn) batteries have attracted tremendous attentions. However, most of the present binder-free cathodes suffer from low areal capacity and energy density, which severely restrict their practical applications. Herein, we demonstrate an efficient metal-organic framework (MOF)-involved strategy to rationally integration of the active NiCo2O4, CoMoO4 and Co3O4 cathode materials into one hierarchical arrayed structure that uniformly grown on nickel foam (NF) substrate (denoted as NF–NCO@CMO@CO) with a high mass loading of 9.6 ​mg ​cm−2. Such electrode design possesses favorable merits in the aspects of high electrical conductivity, robust arrayed architectures, abundant electrochemical active sites, rich redox reactions, facile ion diffusion and components’ synergetic effect. As a result, the aqueous NiCo//Zn battery based on NF–NCO@CMO@CO binder-free cathode exhibits an ultrahigh areal capacity of 2.51 ​mAh cm−2 at a current density of 2 ​mA ​cm−2, as well as good rate capability and long-term cycling stability. Impressively, the aqueous NF–NCO@CMO@CO//Zn battery shows a maximum areal energy density of 4.09 ​mWh cm−2 (corresponding to 424.5 ​Wh kg−1), which is superior to most of the previously reported aqueous NiCo//Zn batteries. Electrode reaction kinetics analysis reveals that both capacitive and diffusion-controlled behaviors are involved during the charge storage processes. Moreover, a quasi-solid-state NF–NCO@CMO@CO//Zn battery is also assembled by replacing the liquid electrolyte with gel electrolyte, suggesting the potential for practical applications. This work might shed light on the rational construction of advanced binder-free cathodes for high-performance aqueous NiCo//Zn batteries.

Glycine-assisted solution combustion synthesis of NiCo2O4 electromagnetic wave absorber with wide absorption bandwidth

Design of high-performance electromagnetic (EM) wave absorbing materials has been regarded as an effective solution to excessive EM wave interference problem. As a promising candidate, NiCo2O4 absorbers have attracted enormous research attentions. However, currently reported morphology-manipulation synthetic methods of NiCo2O4 absorbers are time-consuming and require high energy consumption, which inhibit their practical applications. Herein, a more facile and cost-effective solution combustion synthesis was utilized to fabricate NiCo2O4 materials. The absorber prepared by using glycine as fuel displayed the best EM wave absorption performance. Impressively, ultra wide absorption bandwidth of 7.44 GHz from 10.56 GHz to 18 GHz could be achieved with relatively thin thickness of 2.1 mm NiCo2O4 sample fabricated in this work displayed the widest effective absorption bandwidth (EAB) among reported NiCo2O4-based EM wave absorbing materials so far. In view of its simple and low-cost synthetic process and excellent EM wave dissipation capacity, NiCo2O4 samples in this work showed great feasibility as practical absorber. In addition, our findings may also provide new sight for facile preparation of other high-performance EM wave absorbers by solution combustion synthesis instead of complex morphology-manipulation routes.

Influence of Urea on the Synthesis of NiCo2O4 Nanostructure: Morphological and Electrochemical Studies

The widespread use of miniature electronic devices calls for energy-dense storage strategies. The supercapacitor-based energy storage devices with high areal capacitance are desired energy storage alternative. It is still a challenge to fabricate supercapacitor-based energy devices with consistent performance. The porous metal oxides with large areal capacitance are desired materials for electrode, but there exists a limited understanding of the influence of synthesis parameters on microstructural properties, which largely govern their electrochemical performance. In the present work, hierarchal spinel nickel cobaltite (NiCo₂O₄) nanostructures were synthesized in the presence of the varying amount of hydrolyzing agent via a simple hydrothermal method coupled with a simple post-annealing process. This work focuses on understanding the influence of hydrolyzing agent in controlling the microstructure and hence ensuing electrochemical properties of the NiCo₂O₄ based electrode. Based on the urea hydrolyzing content, the as synthesized NiCo₂O₄ nanostructure varied from the rod, plate to nanoflower. The mesoporous nanostructures, with urea content 1.49 gm, exhibit a sizeable BJH surface area (79.2 m² g-1) and high mesopore volume (0.140 cm³ g-1). Remarkably, the NiCo₂O₄ nanoflower shows high specific capacitance of 3143.451 F/g at 2 mV/s scan rate, 1264.5 F/g at 1 A/g current density, energy density of 56 Wh/kg and power density of 8,400 W/kg in 3 M KOH electrolyte. The capacitance loss after 5000 cycles is 48% at the current density of 10 A/g, indicating their excellent cycling stability. The impressive electrocatalytic activity is largely ascribed to the high intrinsic electronic conductivity, superior mesoporous nanostructures and rich surface Ni active species of the NiCo₂O₄ materials, which can largely boost the interfacial electroactive sites and charge transfer rates indicating promising applications as electrodes in future supercapacitors.

Hollow fibrous NiCo2O4 electrodes with controllable Zn substitution sites for supercapacitors

Abstract This study provides a detailed investigation on using two hollow micron-fibrous Zn-doped NiCo2O4 materials as supercapacitor electrodes. These materials can be easily prepared using a simple hydrothermal, calcination process, employing cotton fiber as a template. By changing the content of metal salts in the precursor, the Zn substitution can be controlled in the octahedral Ni-site (NiOh) and tetrahedral Co-site (CoTd). These results are supported using XRD refinements and XPS fine spectra. Furthermore, the phase structure, morphology and pore characteristics of two Zn-doped samples are characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and N2 adsorption-desorption isotherms. The improved intrinsic conductivity and interfacial diffusion are further verified by ultraviolet-visible (UV-vis) spectroscopy, density of states (DOS), and electrochemical impedance spectroscopy (EIS). When used in supercapacitors, both Zn-modified NiCo2O4 materials, despite the different in substitution sites, show a significant improvement in specific capacitance and cyclic retention. Particularly, the tetrahedral Co-site substitution results in the best electrochemical performance. The fabricated electrode at a current density of 2.0 A g−1 exhibits a high specific capacitance of 1344 F g−1 and good capacitance retention of ∼92% after 3000 cycles.

Fabrication of hybrid supercapacitor device based on NiCo2O4@ZnCo2O4 and the biomass-derived N-doped activated carbon with a honeycomb structure

Highly efficient supercapacitor devices are fabricated with the hybrid nanocomposite material and biomass-derived N-doped activated carbon with tunable morphology, composition and structures. NiCo2O4 materials with different morphologies including spherical, urchin, rod and granular are synthesized using different surfactants. These electrode materials display the maximum specific capacity of 419, 543, 506, and 456 C g−1 at 1 A g−1 respectively in 2 M KOH. The optimized urchin-like NiCo2O4 is hybridized with different concentration of ZnCo2O4 nanosheets. The hybridization process significantly increased the specific capacity to 1029 C g−1 at 1 A g−1 for NiCo2O4@ZnCo2O4-2 (NZC2). In order to make the hybrid supercapacitor device, honeycomb porous structured N-doped activated carbon is prepared with the Ricinus Communis seed. The prepared material shows an interconnected pore structure with a high nitrogen content and exhibits the maximum specific capacity of 236 C g−1 at a current density of 1 A g−1. The hybrid supercapacitor device made from NZC2 and the N-doped activated carbon offers the highest energy density of 101.6 W h kg−1 with the corresponding power density of 1.62 kW kg−1.

Dual-template hydrothermal synthesis of multi-channel porous NiCo2O4 hollow spheres as high-performance electromagnetic wave absorber

Dual-template hydrothermal method was adopted for the synthesis of NiCo2O4 materials. The D-glucose acted as the hard template and the three kinds of soft templates, i.e., nonionic polyvinylpyrrolidone (PVP), anionic sodium dodecyl benzene sulfonate (SDBS) and cationic hexadecyl trimethyl ammonium bromide (CTAB) were selected to synthesize NiCo2O4 materials. We found that the species of the soft templates play significant role in the determination of products’ morphologies. Flower-like, flower-like spherical and multi-channel porous hollow spheres structured NiCo2O4 could be obtained by utilization of PVP, CTAB and SDBS, respectively. When employed as the electromagnetic (EM) wave absorbers, the multi-channel porous NiCo2O4 hollow spheres possessed the best EM wave absorption performance. The reflection loss (RL) value lower than −10 dB was up to 5.44 GHz and could be achieved at thin thickness of 1.8 mm. The minimum RL value corresponding to this thickness reached to −31.1 dB as well. The outstanding EM wave absorption performance was ascribed to the unique multi-channel porous hollow spheres structure, which could provide abundant interfaces between absorbers-air thus promoting the interfacial polarization. Additionally, the multiple reflections and scattering, dipole polarization and eddy current loss conjointly accounted for the superior attenuation behavior. The facile synthetic route and the high EM wave absorption performance of multi-channel porous NiCo2O4 hollow spheres may offer a novel strategy for the preparation of high-performance ferrite EM wave absorbers.

Soft-templating and hydrothermal synthesis of NiCo2O4 nanomaterials on Ni foam for high-performance supercapacitors

Nickel cobalt oxide (NiCo2O4) was successfully grown on the nickel foam by a mild hydrothermal method combined with a simple annealing treatment, utilizing SDS, PVP, CTAB, and PVA as template agents. The effect of different template agents on the morphology and electrochemical performance of NiCo2O4 electrode for supercapacitor was further investigated in detail. The physicochemical properties of the NiCo2O4 materials were examined via the X-ray diffraction and the scanning electron microscopy. It could be seen from the XRD patterns that there were no other clear clutter peaks, which indicated that the purity of the material was relatively high. As shown by the SEM diagram, the prepared NiCo2O4 showed different morphology structures via the addition of the template agent, which exhibited high capacitance and cycling stability. Specially, the NiCo2O4 electrode with the usage of 0.75 g SDS, PVP, CTAB, PVA, and none template agents showed high capacitance of 1357, 1469, 1290.6, 1297.4, and 863.8 F g−1 at 1 A g−1. In addition, asymmetric supercapacitors (ASC) were assembled with the brilliant binary oxides as the positive electrode, activated carbon as negative electrode, and 6 mol/L KOH solution as electrolyte. The ASC device demonstrated a high energy density of 64.76 Wh kg−1 at a power density of 774.8 W kg−1. Remarkably, it still displayed desirable cycle retention of 84.39% over 5000 cycle numbers at a current density of 10 A g−1, and the excellent electrochemical performance suggested its potential application in electrode material for supercapacitor.

Facile Synthesis of Mesoporous Nickel Cobalt Oxide for OER – Insight into Intrinsic Electrocatalytic Activity

AbstractThe development of novel metal oxide catalysts for electrochemical water splitting has been one of the future challenges in catalysis. We present the development of structured spinel based NiCo2O4 materials using in‐situ hydrothermal synthesis and KIT‐6 as a template. Their electron transfer kinetics in the oxygen evolution reaction (OER) at pH 14 are studied. Structuring of NiCo2O4 via KIT‐6 improves the intrinsic catalyst performance, e. g., a lower overpotential of ∼350 mV and a good long‐term stability could be observed compared to 385 mV and poor stability of commercially available NiCo2O4. Kinetic studies provided insights into structure‐activity relations and the nature of the electrode/electrolyte interface. Interestingly, structuring via KIT‐6 increases not only the electrochemical surface area but also the current density accompanied by superior charge transfer capacity.

Facile synthesis of mesoporous NiCo2O4 fibers with enhanced photocatalytic performance for the degradation of methyl red under visible light irradiation

Mesoporous NiCo2O4 fibers were synthesized by the coordination co-precipitation-decomposition method using ammonia as morphology-controller. The as-prepared NiCo2O4 powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–vis absorption spectra and photoluminescence (PL) analysis. The as-prepared NiCo2O4 materials showed typical intertwined porous nanofibrous structures with specific surface area of 74.6 m2/g and average pore size of 11.79 nm. The mesoporous NiCo2O4 fibers showed remarkably enhanced photocatalytic performance towards methyl red (MR) degradation under visible-light irradiation compared to the Co3O4 and NiO. The degradation efficiency of MR over the NiCo2O4 reached up to 95.1% after irradiation for 120 min. Superior photocatalytic activity of 1D NiCo2O4 fibers can be attributed to the higher light harvesting capacity resulted from large surface area and unique mesoporous structure. Finally, a possible mechanism for the photodegradation of MR over the NiCo2O4 was proposed.