Nickel Cobalt Oxide Research Articles

Controllable growth of flower-like hierarchical CoNiO2 nanoflakes anchored on Nitinol fiber substrate with good selectivity for highly efficient solid-phase microextraction of polycyclic aromatic hydrocarbons in water

The flower-like hierarchical cobalt nickel oxide nanoflakes (CoNiO2NFs) with a porous structure were fabricated on Nitinol (NiTi) fiber substrate by a hydrothermal reaction and subsequent annealing treatment. The morphology affected by the molar ratios of Ni to Co and counter ions in starting precursors as well as hydrothermal reaction temperature and time was investigated in detail. The obtained CoNiO2NFs coating exhibited outstanding performance for the selective extraction of PAHs. After optimizing the main parameters that affected extraction through orthogonal experiments, the developed method showed good linearity in the ranges of 0.05 μg L−1 - 200 μg L−1 with the determination coefficient >0.999. LODs were between 0.006 μg L−1 and 0.114 μg L−1, LOQs were in the ranges of 0.020–0.376 μg L−1 and RSDs were below 5.19% and 5.71% for intra-day and inter-day analyses, respectively. The developed method was successfully applied to selective enrichment and determination of target PAHs in real water samples. Moreover, the fabricated fiber exhibited high chemical and mechanical stability, and could withstand more than 260 extraction-desorption cycles without loss of its extraction efficiency.

High-Energy Asymmetric Supercapacitor Based on the Nickel Cobalt Oxide (NiCo2O4) Nanostructure Material and Activated Carbon Derived from Cocoa Pods

Nickel cobalt oxide (NiCo2O4) nanoagglomerates were effectively synthesized through a simplistic low-temperature co-precipitation technique. The obtained material was further calcined to enhance its morphological properties and reduce the size of its individual particle of agglomerates. The as-synthesized NiCo2O4 agglomerates were characterized through the employment of various techniques, which include scanning/transmission electron microscopies (SEM/TEM), X-ray diffraction, Raman spectroscopy and X-ray fluorescence spectroscopy (XRF), and thermogravimetric analysis (TGA). Electrochemical performances of the as-synthesized electrode materials evaluated in a three-electrode configuration could deliver an optimized specific capacity of 95.6 mA h g–1 at a 0.5 A g–1 specific current. A fabricated hybrid asymmetric supercapacitor (SC) composed of NiCo2O4 and the activated carbon obtained from cocoa pods (Cocoa AC-700) as the positive and negative electrodes (NiCo2O4//AC cocoa-700), respectively, delivered a specific capacity of around 168.7 mA h g–1 at 0.5 A g–1 and a corresponding specific energy and power of 47.7 W h kg–1 and 430.0 W kg–1, respectively. The SC exhibited a substantial cycling stability, resulting in a Coulombic efficiency of 97.2% with a related capacity retention of 96.6% recorded after a cycling test of over 11,000 cycles at 5 A g–1.

Electrochemical behavior of nickel cobalt oxide micro-flowers in different electrolytic systems

Here, nickel cobalt oxide micro-flowers (NCO-F) have been prepared by the hydrothermal method for their application as electrode material in supercapacitors. The electrochemical performance of the prepared material has been studied in three different aqueous electrolytes (1 M Na2SO4, 1 M KOH, and 1 M Na2SO4 with hydroquinone (Hq) and benzoquinone (Bq) as redox additives). The NCO-F shows maximum specific capacitance in 1 M KOH (470 Fg−1) followed by 1 M Na2SO4 with Hq and Bq additives (173 Fg−1) and 1 M Na2SO4 (101 Fg−1) at the scan rate of 5 mVs−1. However, the higher value of energy density and power density is obtained in 1 M Na2SO4 (35.80 Whkg−1 at 424 Wkg−1). This is because of the higher potential window possessed by NCO-F in 1 M Na2SO4. The results illustrate that the role of the potential window is important which in turn is governed by the type of electrolyte.

Bimetallic nickel-cobalt oxides: A comprehensive insight into Ni/Co ratio, intrinsic structure and electrochemical behaviors

As a widely explored batty-type electrode materials, bimetallic nickel-cobalt oxides with different Ni/Co ratios were synthesized. The influence of Ni/Co ratios on the as-synthesized products is emphasized and systemically studied from the aspect of morphology and microstructure, phase and composition, electrochemical performance, activity as well as energy storage mechanism. The results demonstrated the dependence of phase and composition, morphology and microstructure on Ni/Co ratios. When nickel and cobalt nitrate coexist in the reactant, the as-prepared samples are composed of multiphases instead of a single-phase material. Ni/Co ratio of the reactant is not necessarily related to the proportion of nickel and cobalt of the product. Therefore, it is recommended that the author should clearly state the nickel/cobalt ratio in the product rather than in the reactant. Additionally, the capacity of all samples is mainly originated from pseudo-capacitive capacity, demonstrating a more capacitive behavior in nickel-cobalt oxides. Moreover, theoretical calculation verified that nickel/cobalt substitution could lower OH− adsorption energy and facilitate the electrochemical activity on the active site. This paper conducts a comprehensive understanding of the influence of component and microstructure on electrochemical energy storage behaviors of nickel-cobalt-based oxides, which has a certain value for the follow-up study of nickel-cobalt-based compounds.

Simultaneous electrochemical deposition of nickel cobalt oxide-reduced graphene oxide composites for high performance asymmetric supercapacitors

In this work, a one-step electrodeposition approach was applied for nanosheets fabrication of binder free nickel cobalt oxide (NCO) and NCO-reduced graphene oxide (NCO-rGO) composites on the nickel-foam substrate by repetitive cyclic voltammetry (rCV). The NCO-rGO hybrids were firstly fabricated on Ni foam surface with the reduction of GO and electrodeposition of NCO simultaneously. Interaction of NCO particles with rGO sheets increased the conductivity of the composite and consequently facilitated the electron transfer rate. Electrochemical measurements proved that specific capacitance and cyclic performance of as-prepared materials were improved with the synergistic effect of rGO in the hybrid structure. The optimized NCO-rGO electrode exhibited a specific capacitance of 1916.5 F g−1 at 1 A g−1 with superior stability of 95.6% at a high current density of 10 A g−1 even after 3000 cycles. To explore its practical applications, an asymmetric supercapacitor (ASC) based on NCO-rGO as a positive electrode and rGO as a negative electrode was constructed, which exhibited a prominent specific energy of 45.22 Wh kg−1 at 400 W kg−1. As a result, NCO-rGO hybrid structure as the functional electrode material for the supercapacitors with remarkable electrochemical performance were obtained, thanks to the increased conductivity and decreased mass by removing binders.

Polymerization of lactic acid produced from food waste by metal oxide-assisted dark fermentation

Lactic acid (LA) is the precursor monomer used in the production of biodegradable and eco-friendly polylactic acid (PLA) polymer. The purpose of this study was to first determine the role of nano-metal oxides in improving the production of L-LA from food waste via the dark fermentation process and then to compare the conversion of L-LA to PLA using conventional and novel catalysts. Compared to the control run without nanoparticles (NPs) addition, maximum L-LA concentration (38.86 g/L), yield (0.194 g/g- TS), and productivity (3.88 g/L-day) were achieved for iron oxide (FeOx) nanoparticles (NPs)-assisted fermentation at an optimal dosage of 15 mg/L. Nickel oxide (NiOx) and cobalt oxide (CoOx) NPs also showed similar enhancing effects for L-LA production. However, high dosages of the metal oxide NPs decreased the LA production in the medium. Moreover, a new nanocatalyst, iron phosphate (FePO4), was prepared and examined for PLA production from the as-synthesized L-LA monomeric units by ring-opening polymerization. A high yield of lactide (84.71%) was produced in a shorter reaction time (10 h) using FePO4 than the conventional tin chloride (SnCl2) catalyst. PLA polymer with molecular weights in the range of 4,900–5,200 Da was obtained using FePO4 and tin chloride dihydrates (SnCl2) catalysts under the optimized conditions. As such, this work has demonstrated a practical way to improve LA production from organic waste streams and its effective conversion to PLA for potential applications in the biomedical and bioplastic sectors.

Development of Three-Dimensional Nickel-Cobalt Oxide Nanoflowers for Superior Photocatalytic Degradation of Food Colorant Dyes: Catalyst Properties and Reaction Kinetic Study.

In this work, we present three-dimensional flower-like nickel-cobalt oxide (F-NCO) nanosheets developed in a facile, eco-friendly hydrothermal route to apply as photocatalysts for food colorant Allura Red AC dye removal under light illumination. Using Brunauer-Emmett-Teller analysis, it was found that the F-NCO nanosheets displayed a surface area of ∼53.65 m2/g and a Barrett-Joyner-Halenda pore size of ∼14 nm, which was also confirmed by the calculated crystallite size of ∼15 nm using powder X-ray diffraction (XRD) analysis. From Williamson-Hall analysis of XRD spectra, F-NCO nanosheets revealed a crystal-lattice strain of ∼3.42 × 10-3 and a dislocation density of ∼4.397 × 1015 lines/m2 in the crystal structure. Transmission electron microscopy analysis revealed that F-NCO nanosheets accumulated to form flower-like nanostructures of <100 nm length with a d-spacing of ∼2.6 Å, which is attributed to the (311) crystallographic plane (α = γ = β = 90°, a = b = c = 8.110 Å, JCPDS No. 00-020-0781) of the cubic phase. The F-NCO nanosheets exhibited an excellent photocatalytic efficiency of ∼94.75% in ∼10 min with sodium borohydride under UV light. The Langmuir-Hinshelwood model determined pseudo-first-order reaction kinetics of dye degradation using the versus time plot. The kinetic study produced a first-order rate constant (k) of ∼0.219 min-1, resulting in ∼3.16 min half-life (t1/2) for the F-NCO-catalyzed degradation reaction. Thus outstanding photocatalytic performance of F-NCO nanosheets would display their huge potential for organic-pollutant removal from water with exceptional recyclability for wide research applications in the future.

A New Insight into the Simulation of Blended Electrodes

State-of-the-art lithium ion batteries often use blended electrodes to enhance performance. Many electric vehicles are using a mix of Lithium Manganese Nickel Cobalt oxide (NMC) and Lithium Manganese oxide (LMO) as positive electrodes and most newer batteries are using a mix of Silicon oxide (SiOx) and graphite (G) as negative electrodes. The blended nature of the electrodes is complicating electrode modeling and the diagnosability of cell degradation. Relatively few modeling studies are considering blended electrodes and those that do often assume that both components of the electrodes are subject to the same current.HNEI previously investigated the current distribution in blended electrodes by testing different materials in parallel to mimic the blending. We used a custom experimental set-up to test material couples with distinct (LFP+LMO), fully overlapping (NMC+NCA) and partially overlapping (G+SiOx and NMC+LMO) electrochemical responses. Results indicated that the constant current hypothesis for simulating blends might only be valid for materials whose electrochemical behaviors are separate or completely overlapping. In such cases, the current on each component of the blend is either equal to that of the applied current if the electrochemical active ranges are separated or pondered if the active ranges overlap. If the electrochemical behaviors do not fully overlap, the constant current hypothesis appears invalid. This work will present the mechanistic modeling results associated with these complex current distributions and showcase that a constant current approach, like the one used previously, might not be the most accurate.

Dicobalt Nickel Oxides With a Sugar-Based Carbon Precursor for Water Splitting Applications

In order to effectively reduce carbon emissions and achieve the goal of providing alternate energy sources hydrogen energy has high hopes as a representative of new energy. According to current research compounds of cobalt and nickel have been widely studied as alternative noble metal materials as catalysts for electrolysis of water. Based on other research reports, a simple hydrothermal method is proposed to grow cobalt-nickel oxide on nickel foam that has been pre-carbonized with a glucose source in advance. In order to compare the modification results of the materials by different activation methods high-temperature treatment and sulfurization of the materials were carried out. Among them, the sulfurized material not only has a relatively good performance in the catalytic reaction of hydrogen evolution and oxygen evolution but also has a good performance as an energy storage material for supercapacitors.

One-step preparation of cobalt nickel oxide hydroxide@cobalt sulfide heterostructure film on Ni foam through hydrothermal electrodeposition for supercapacitors

Development of technologies or strategies to achieve efficient and low-cost electrode materials for high-performance supercapacitors is highly desirable in the field of renewable energy. In this study, a novel route for preparation of a two-phase film of 4Ni(OH)2·NiOOH@Co9S8 on Ni foam was developed through chemical bath followed by hydrothermal electrodeposition, which was carried out by a one-step process in an autoclave. This strategy first grew nano-sheets of 4Ni(OH)2·NiOOH phase crystals (NiCo-OH) on Ni foam in the stage of elevating temperature, and then start to deposit Co9S8 phase species (CoS) onto the surface of NiC-oOH through hydrothermal electrodeposition during heat preservation, forming a cheek to cheek heterostructure. The resultant composite film as an electrode material for supercapacitors could deliver specific capacities of 1083.6 (2.709), 856.8 (2.142), 624.6 (1.562), 502.2 (1.256), 419.4 (1.049) and 279.2 (0.698) C·g−1 (C·cm−2) at 5, 10, 20, 30, 40 and 50 mA·cm−2, and long lifespan (no decay after 12,000 cycles), which is far higher than the single NiCo-OH film. The excellent capacitive performance is ascribed to the synergistic effect of NiCo-OH and CoS which could provide fast ion and electron conductions, respectively. When the NiCo-OH/CoS composite was utilized as the positive electrode material and active carbon as the negative material, an asymmetric supercapacitor device (ASC) was assembled and could achieve high specific capacitance (1.52 F·cm−2 at 5 mA·cm−2), good rate capability (a capacitance retention of 59% with an 10-fold increase in the discharge current density), high energy density (8.2 Wh·kg−1 (15.1 mWh·cm−3) at 542.8 W·kg−1 (111.1 mW·cm−3)), high power density (5440.2 W·kg−1 (1111.1 mW·cm−3) at 39.8 Wh·kg−1 (8.1 mWh·cm−3)) and excellent cycling stability (a capacitance retention of 85.5% after 12,000 cycles). The results prove that this novel strategy exhibits a promising prospect of direct fabrication of a heterostructure electrode with advantageous features, like convenience and time/cost saving, for high-performance supercapacitors.

In-situ formed hierarchical transition metal oxide nanoarrays with rich antisite defects and oxygen vacancies for high-rate energy storage devices

Developing transition metal oxides (TMOs) with high energy, power, and long cycle lifetime for electric energy storage devices remains a critical challenge to date. Herein, we demonstrate a facile method that enables in-situ transformation of nickel cobalt oxide nanowire arrays (NiCoO NWA) into hierarchical nanowire-nanosheet arrays (ac-NiCoO NWSA) for enhanced energy storage properties. More specifically, the method leads to formation of atomically thin nanosheets (only 2.0 nm) and creates abundant antisite defects and oxygen vacancies. Owing to these merits, the as-prepared ac-NiCoO NWSA electrode exhibits over five-fold higher specific capacity, superior rate capability (up to 100 A/g), and excellent cycling stability of 10,000 cycles at 50 A/g in alkaline electrolyte compared to pristine NiCoO NWA. Density functional theory (DFT) simulations elucidate the electrochemical activity enhancement mechanism of the TMOs. Moreover, our method triggers similar structural reconstruction phenomenon on other TMOs including ZnCo-, CoMn- and ZnNiCo-oxides, proving the universality of the method. Our findings provide a general method towards simultaneously manipulating the micro-morphologies and defects of TMOs for advanced energy storage devices.

Three-dimensional NiCo2O4 nanosheets arrays on carbon nanofibers for high-performance asymmetric solid-state supercapacitor

A hybrid nanocomposite (NCO-CNF) with 3D hierarchical porous nickel cobalt-oxide (NCO) nanosheets structure was successfully constructed on the surface of the N-doped carbon nanofiber (CNF) through the combination of electrospinning, hydrothermal and heat-treatment process, where the CNF as a structural scaffold and excellent conductor to improve the conduction of electrons and effectively prevent aggregation of NCO-CNF nanosheets. Thus, generating a synergistic electrochemical enhancement through maximize utilization of two components and strong coupling interaction between 1D CNF and 2D NCO nanosheets. The resultant NCO-CNF delivered outstanding specific capacitance as high as 343 F g−1 in three electrode system. Furthermore, the obtained NCO-CNF can as the positive electrode while the CNF serves as the negative electrode to assemble the solid asymmetric supercapacitor and the energy density of NCO-CNF//CNF is up to 44.8 Wh kg−1 (44.8 μWh cm−2). This work leaves more strategies for utilizing effectively 2D nanomaterials and carbon fiber.

Nickel doped Nano Cobalt (II) Oxide used as Photocatalyst for Degradation of Evans Blue Dye

The photocatalytic degradation of Evans blue (EB) has been studied under visible light in the presence of nanocrystalline nickel doped cobalt (II) oxide as a photocatalyst. Nickel-cobalt (II) oxide was synthesized by using Sol-gel technique. The photocatalyst was characterized by Field Emission Scanning Electron Microscopy (FESEM), Energy-dispersive X-ray spectroscopy (EDX), X-ray Diffraction (XRD), Fourier-transform infrared (FTIR) and High-resolution transmission electron microscopy (HRTEM). Effect of various working parameters like pH, concentration, amount of nickel doped and undoped cobalt (II) oxide, dose of dopants, light intensity etc. on the rate of degradation of Evans blue was also investigated. On the basis of observations, a suitable mechanism for the photocatalytic degradation of Evans blue dye has been proposed.

Hierarchical NiCo / NiO / NiCo 2 O 4 composite formation by solvothermal reaction as a potential electrode material for hydrogen evolutions and asymmetric supercapacitors

Electrochemical energy storage and conversion mechanisms are highly viable routes in the current scenario, and hence supercapacitor and electrolysis of water splitting have gained significant attention in recent times. Thus, transition metal nickel cobalt oxides are widely inspected as promising electrode materials for electrocatalysis and supercapacitors. However, the pure NiCo2O4 was highly hindered by its widespread uses due to low electronic conductivity and deficient active edges. This study is aimed to fabricate the NiCo/NiO/NiCo2O4 composite using a solvothermal process with different ratios of solvents. The inherent NiCo/NiO/NiCo2O4 composite holds plentiful active edges and improved electrical conductivity than the pure. Interestingly, the electrocatalytic results revealed that the NiCo/NiO/NiCo2O4 (NC) composite prepared by a solvent ratio of (double distilled water (DDW) to N, N-Dimethylformamide (DMF)) 2:1 (NC1) displayed the small overpotentials of 144 and 142 mV to realize 10 mA cm−2 with the robust durability during a 24 hours hydrogen evolution reaction (HER) test in the acid and alkaline electrolyte, respectively. Moreover, the designed NC1 composite as a supercapacitor electrode exhibited considerable capacitance of 638 F g−1 at a current density of 1 A g−1. In comparison, the analog DDW to DMF ratio 1:1 (NC2) and 1:2 (NC3) structures showed 514 F g−1 and 415 F g−1, respectively. Further, a dual-electrode device was fabricated using the NC1 composite and activated carbon, exhibited an energy density of 28.14 W h kg−1 at 414.45 W kg−1 power density with excellent device stability (89.4%) for 10 000 charge/discharge cycles.

Synergistic engineering of morphology and electronic structure in constructing metal-organic framework-derived Ru doped cobalt-nickel oxide heterostructure towards efficient alkaline hydrogen evolution reaction

Hydrogen generation by alkaline electrochemical water splitting urgently requires new techniques capable of fabricating efficient and robust electrocatalysts for hydrogen evolution reaction (HER). However, it remains a major challenge to achieve this aim through a conjoint modulation in morphology and electronic structure. Herein, a metal–organic framework-derived (MOF-derived) Ru doped cobalt–nickel oxide heterostructure grown on Ni foam (Ru-Co3O4-NiO-NF) is fabricated by a simple and scalable preparation method. Systematic experimental characterizations verify that through a tailored low-temperature annealing process, the resulted Ru-Co3O4-NiO-NF can effectively inherit the advantageous two-dimensional (2D) nanosheet morphology of Co-MOF precursor and simultaneously maintain the mechanical robustness of three-dimensional (3D) Ni foam, which are beneficial for active site exposure and charge or mass transport. Furthermore, X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculation are hired to reveal that Ru-doping and Co3O4-NiO heterointerface can collectively regulate the electronic state of Ni and Co sites, thus optimizing the H2O adsorption/desorption and proton adsorption in alkaline HER process. As expected, the optimized Ru-Co3O4-NiO-NF is much more active than the commercial Pt-C (20 wt%) for electrocatalytic HER in 1 M KOH, exhibiting the low overpotential of 44 mV and 115 mV at the current density of 10 mA cm−2 and 100 mA cm−2. Moreover, the obtained self-supported electrode material can maintain catalytic activity over 60 h at 100 mA cm−2 without significant decay. This study provides a new perspective for constructing the advanced MOF-derived alkaline HER self-supported electrocatalysts by synergistic engineering of morphology and electronic structure for future energy application.

Effect of cobalt (nickel) oxide on the properties of zinc\u2013titanium sorbents for high temperature desulphurization of model coal gas

Zn–Ti–Co(Ni) sorbents for H2S removal from model hot coal were prepared and characterized. Effects of cobalt (Co) and nickel (Ni) on the sorbents texture, structure, H2S sorption capacity and regeneration properties were determined. TiO2 formed mixed metal oxides with CoO and NiO in the fresh sorbents, while TiO2 and nanocrystalline sulfides of Zn, Co, Ni were found in sulphided ones. The oxidative regeneration of sulphided sorbents re-formed mixed oxides. Sorption capacity of studied materials increased along with an increase of the amount of added Co (Ni) and also with the number of work cycles. Co-doped Zn–Ti materials adsorbed up to 244% more sulfur than these of Zn–Ti, while Ni-doped materials adsorbed ca. twice more H2S than the corresponding Co-doped sorbents. The addition of Co (Ni) decreased the temperature of ZnS oxidation. The catalytic effect of the Co (Ni) oxides on the oxidation of ZnS was suggested.

Nanoflakes-like nickel cobaltite as active electrode material for 4-nitrophenol reduction and supercapacitor applications

Catalytic reduction of nitroaromatic compounds present in wastewater by nanostructured materials is a promising process for wastewater treatment. A multifunctional electrode based on ternary spinal nickel cobalt oxide is used in the catalytic reduction of a nitroaromatic compound and supercapacitor application. In this study, we designed nanoflakes- like nickel cobaltite (NiCo2O4) using a simple, chemical, cost-effective hydrothermal method. Nanoflakes- like NiCo2O4 samples are tested as catalysts toward rapid reduction of 4-nitrophenol and as electrode materials for supercapacitors. The conversion of 4-nitrophenol into 4-aminophenol is achieved using a reducing agents like sodium borohydride and NiCo2O4 catalyst. Effect of catalyst loading, 4-nitrophenol and sodium borohydride concentrations on the catalytic performance of 4-nitrophenol is studied. As sodium borohydride concentration increases the catalytic efficiency of 4-nitrophenol increased due to more BH4- ions available which provides more electrons for catalytic reduction of 4-nitrophenol. Catalytic reduction of 4-nitrophenol using sodium borohydride as a reducing agent was based on the Langmuir–Hinshelwood mechanism. This mechanism follows the apparent pseudo first order reaction kinetics. Additionally, NiCo2O4 electrode is used for energy storage application. The nanoflakes-like NiCo2O4 electrode deposited at 120 °C shows a higher specific capacitance than samples synthesized at 100 and 140 °C. The maximum specific capacitance observed for NiCo2O4 electrode is 1505 Fg−1 at a scan rate of 5 mV s−1 with high stability of 95% for 5000 CV cycles.

Nanostructured Nickel-Cobalt Oxide and Sulfide for Green Energy Production Using Waste Water

With the advancement in technology, demand for green energy production is increasing year by year. To meet the increasing demand for green energy, there has been continuous research in a bid to find better materials and efficient ways to generate energy. Transition metals such as Fe, Mo, Ni, etc. based materials have shown great potential to be used as electrocatalysts for water splitting, and the urea oxidation reaction (UOR). In this work, nanostructured nickel-cobalt oxide and nickel-cobalt sulfide were synthesized using a facile hydrothermal method for their applications in water splitting and UOR. It was observed that the properties of nickel-cobalt oxide improved significantly after converting it to nickel-cobalt sulfide. Nickel-cobalt sulfide showed an overpotential of 282 mV while nickel-cobalt oxide displayed an overpotential of 379 mV to generate a current of 10 mA/cm2 , towards oxygen evolution. After introduction of 0.33 M urea, the potential for oxidation of urea for both nickel-cobalt oxide and nickel-cobalt sulfide is decreased to 1.34 V.

Two dimensional layered nickel cobaltite nanosheets as an efficient electrode material for high‐performance hybrid supercapacitor

Nickel cobalt oxide (NCO) is considered an auspicious electrode candidate for the reinforcement of energy-storage devices. Currently, an immense interest is devoted to modifying the morphological aspects of the NCO to boost their surface texture and electrochemical performances, which is feasible for the development of high energy density and durable devices. Herein, we report the synthesis of layered NCO nanosheets via solvothermal reaction by tuning the solvent volume ratio (water/N,N-Dimethylformamide [DMF]) for supercapacitor electrode material. The nickel cobalt oxide is prepared utilizing a 1:2 (DMF:water) ratio of solvent (NCO1) displays a controlled growth of 2D nanosheets with excellent surface texture. Moreover, NCO1 demonstrates the battery type charge storage properties with a maximum specific capacitance (Csp) of 731 F g−1, which is far better than NCO2 (623 F g−1) and NCO3 (556 F g−1) prepared in other solvent proportions. Besides, the constructed hybrid supercapacitor utilizing activated carbon (AC) and NCO1 as the negative and positive electrodes, respectively, exhibits the Csp of 120 F g−1, and maximum specific energy 37.33 W h kg−1 for the specific power 691.31 W kg−1 and demonstrates excellent stability ~80.56% for 20 000 cycles.

Graphene oxide template based synthesis of NiCo2O4 nanosheets for high performance non-enzymatic glucose sensor

While glucose detection is ruled by enzyme-based glucose test strips, the chemically and thermally sensitive enzymes motivate the researchers to inspect chemically and thermally stable metal oxides as alternate sensing constituents for non-enzymatic glucose detection. Here, we report a synthesis of spinel nickel cobalt oxide (NiCo2O4) nanosheets-based catalyst for enzyme-free glucose sensing application via sonochemical approach using graphene oxide (GO) as nanosheets template and zeolitic imidazolate frameworks (ZIF-67) type nickel-cobalt metal-organic frameworks as oxide precursors (the catalyst named as gt-NiCo2O4 NSs). The physical characterization techniques confirmed that the as-synthesized gt-NiCo2O4 exhibited uniform porous and nanosheets morphology which can be obtained due to the ZIF-67 and GO template, respectively. Cyclic voltammetry and amperometric techniques employed for glucose oxidation at + 0.55 V using gt-NiCo2O4 NSs electrode in 0.1 M KOH. This sensor exhibited an excellent linear range (150 nM–8.86 mM), sensitivity (729.72 µA mM−1 cm−2) and lower detection level (7.35 nM; S/N ratio = 3) to glucose. Interestingly, the gt-NiCo2O4 NSs electrode displayed good recoveries to glucose in human blood serum and urine samples. Hence, the results indicates that gt-NiCo2O4 NSs is a promising electrode matrix with high sensitivity, excellent stability and good reproducibility that can enable the progress of enzyme-free glucose sensors.