Hierarchical NiCo2O4 Research Articles

Synthesis of hollow NiCo2O4 nanospheres with large specific surface area for asymmetric supercapacitors

Hollow micro-/nanostructured electrode materials with high active surface area are highly desirable for achieving outstanding electrochemical properties. Herein, we report the successful synthesis of hierarchical hollow NiCo2O4 nanospheres with high surface area as electrode materials for supercapacitors. Electrochemical measurements prove that such electrode materials exhibit excellent electrochemical behavior with a specific capacitance reaching 1229 F/g at 1 A/g, remarkable rate performance (∼83.6% retention from 1 to 25 A/g) and good cycling performance (86.3% after 3000 cycles). Furthermore, the asymmetric supercapacitor is fabricated with hollow NiCo2O4 nanospheres electrode and activated carbon (AC) electrode as the positive and negative, respectively. This device exhibits a maximum energy density of 21.5 W h/kg, excellent cycling performance and coulombic efficiency. The results show that hollow NiCo2O4 nanosphere electrode is a promising electrode material for the future application in high performance supercapacitors.

Facile preparation of urchin-like NiCo2O4 microspheres as oxidase mimetic for colormetric assay of hydroquinone

The hierarchical urchin-like NiCo2O4 microspheres were successfully fabricated by facile two-step method, including template-free hydrothermal and calcination. The prepared NiCo2O4 microspheres with amounts of absorbed oxygen were found to possess oxidase-like activity. They could catalytically oxidize 3,3′,5,5′-tetramethylbenzidine (TMB) without the exogenous addition of H2O2, causing typical color reaction. But hydroquinone (HQ) could induce the reduction of oxTMB and result in a conspicuous blue color fading. In this paper, a simple and rapid colorimetric method for detecting trace amount of HQ was explored in-depth. Excellent linear relationship (5–110μM) and a low detection limit of 2.7μM were achieved. Meaningfully, this method could be well applied in real environmental samples with outstanding recoveries ranging from 97.07% to 103.52%. These primary results demonstrated that the NiCo2O4 microspheres have a great potential for applications in environmental chemistry.

Polypyrrole-Decorated Hierarchical NiCo2O4 Nanoneedles/Carbon Fiber Papers for Flexible High-Performance Supercapacitor Applications

A novel polyprrole (PPy)-decorated hierarchical NiCo2O4 nanoneedles was grown on highly conductive carbon fiber paper (CFP) for high performance asymmetric supercapacitor applications. The PPy-decorated hierarchical NiCo2O4 nanoneedle on CFP (PPy-NiCo2O4@CPF) was grown by two steps. At first, NiCo2O4 nanoneedle was grown by hydrothermal process and followed by the deposition of PPy through electrochemical method. The fabricated PPy-NiCo2O4@CPF electrode displayed the higher electrochemical performance. The specific capacitance was ∼910F g-1 at a current density of 1Ag−1 and cyclic stability was ∼88% after 10,000 cycles. To explore real performance of the electrode, we have fabricated solid state asymmetric supercapacitor using PPy-NiCo2O4@CFP as positive and nitrogen doped reduced graphene oxide (N-rGO) as negative electrodes. The fabricated asymmetric device delivered a specific capacitance of 118.6F g-1 at a current density of 1.0Ag−1 with a maximum energy density of 40.81WhKg−1 (at a power density of 738.27WKg−1) and maximum power density of 3746.77WKg−1 (at an energy density of 13.53WhKg−1). The impressive results suggest that flexible PPy-NiCo2O4@CFPs can be a promising electrode material for supercapacitor applications.

Self-templated formation of hierarchical NiCo2O4 yolk-shell microspheres with enhanced electrochemical properties

Novel hierarchical NiCo2O4 microspheres with a yolk-shell structure are successfully constructed via a two-step synthetic method combining a facile and scalable spray pyrolysis with a simple but powerful heat treatment process. Polyvinylpyrrolidone (PVP) dissolved in precursor solution is used as a functional template playing a vital role in structural design. Hierarchical carbon combustion reactions of NiO@CoO@C precursor powder produce yolk-shell structure during the heat-treatment process. Heat-treated temperatures can be adjusted to obtain different structured nickel-cobalt oxide microspheres. As a potential anode material for Li-ion batteries, the hierarchical yolk-shell NiCo2O4 microspheres exhibit a large reversible specific capacity of 984mAhg−1 at a high current density of 1000mAg−1 after 100 cycles, representing a high capacity retention of 98.2%. When operating at a current density of 5Ag−1, it delivers ultrafast charge-discharge performance, exhibiting a high capacity of 813mAhg−1. These excellent electrochemical properties very likely originate from characteristic yolk-shell structures, which provide buffer areas for the enormous volume expansion caused by Li-ion insertion/extraction and shorten the diffusion path of Li ions by increasing the contact area between the electrode and the electrolyte. This work may serve as a reference for the design of structurally novel functional materials in other advanced energy conversion and storage areas, such as supercapacitors, lithium–sulfur batteries, fuel cells, and Na-ion batteries.

Hierarchical NiCo2O4 nanowalls composed of ultrathin nanosheets as electrode materials for supercapacitor and Li ion battery applications

In this work, NiCo2O4 nanowalls composed of ultrathin nanosheets are fabricated successfully on Ni foam by a facile one-pot solvothermal method followed by thermolysis of the precursors. The as-prepared NiCo2O4 products are evaluated as electrode materials for supercapacitors and lithium ion batteries. The results show high discharge capacitance of 925mF/cm2 at a current density of 5mA/cm2, with remarkable cycling stability (about 24.2% loss after 6000 cycles) and excellent rate performance (71.5% capacitance retention with current density range from 1mA/cm2 to 20mA/cm2). In addition, Ni foam supported NiCo2O4 nanowalls possess excellent discharge capacity of 1100mAh/g as lithium ion battery anode at a current density of 100mA/g. The excellent electrochemical performance of NiCo2O4 nanowalls could be ascribed to the unique spatial structure composed of interconnected ultrathin nanosheets, which facilitates ion penetration and electron transportation, demonstrating their potential applications as electrode materials for high performance supercapacitors and lithium ion batteries.

3D flower-like NiCo 2 O 4 electrode material prepared by a modified solvothermal method for supercapacitor

Novel 3D hierarchical mesoporous flower-like NiCo2O4 electrode material was prepared by water-ethanol mixed solvothermal method combining the calcination process. Nickel sulfate hexahydrate (NiSO4·6H2O), cobalt sulfate heptahydrate (CoSO4·7H2O), rare-used guanidine (CH6ClN3) were used as nickel and cobalt sources, precipitant of weak base, respectively. The resultant samples were characterized by X-ray diffraction, scanning electron microscopy, N2 adsorption and desorption and transmission electron microscopy. The prepared NiCo2O4 material exhibited excellent electrochemical performance-with a high specific capacitance of 1609 F g−1 at 1 A g−1, and high capacity retention of 85% after a 1000-cycle charge-discharge at 10 A g−1.

ZnWO4 nanoflakes decorated NiCo2O4 nanoneedle arrays grown on carbon cloth as supercapacitor electrodes

We have successfully realized a high-capacity, good-rate-capability, and long-life supercapacitor electrode by developing the hierarchical 3D NiCo2O4 nanoneedle arrays (NNAs)@ZnWO4 nanoflakes (NFs) core-shell structures on carbon cloth (CC) for the first time. The free-standing CC@NiCo2O4@ZnWO4 electrode gives rise to a high specific capacity of 296.5Cg−1 at a current density of 0.5Ag−1 and 269.0Cg−1 even at 10Ag−1, and retains ∼90.1% of the capacity even after 5000 cycles of charge and discharge. Compared with CC@NiCo2O4 electrode, the remarkable electrochemical behaviors demonstrate that ZnWO4 NFs decorated NiCo2O4 NNAs on CC as a new type of electrode is highly desirable for application as high-performance electrochemical supercapacitors.

Hierarchical NiCo₂O₄ Hollow Sphere as a Peroxidase Mimetic for Colorimetric Detection of H₂O₂ and Glucose.

In this work, the hierarchical NiCo2O4 hollow sphere synthesized via a “coordinating etching and precipitating” process was demonstrated to exhibit intrinsic peroxidase-like activity. The peroxidase-like activity of NiCo2O4, NiO, and Co3O4 hollow spheres were comparatively studied by the catalytic oxidation reaction of 3,3,5,5-tetramethylbenzidine (TMB) in presence of H2O2, and a superior peroxidase-like activity of NiCo2O4 was confirmed by stronger absorbance at 652 nm. Furthermore, the proposed sensing platform showed commendable response to H2O2 with a linear range from 10 μM to 400 μM, and a detection limit of 0.21 μM. Cooperated with GOx, the developed novel colorimetric and visual glucose-sensing platform exhibited high selectivity, favorable reproducibility, satisfactory applicability, wide linear range (from 0.1 mM to 4.5 mM), and a low detection limit of 5.31 μM. In addition, the concentration-dependent color change would offer a better and handier way for detection of H2O2 and glucose by naked eye.

Interconnected hierarchical NiCo2O4 microspheres as high-performance electrode materials for supercapacitors.

Herein, interconnected hierarchical NiCo2O4 microspheres (IH-NiCo2O4) were prepared via a solvothermal method followed by an annealing treatment. IH-NiCo2O4 possesses large tunnels and abundant mesopores, which are in favor of their applications in energy storage field. When employed as an electrode material for supercapacitors, IH-NiCo2O4 exhibits a high specific capacitance of 1822.3 F g-1 at a current density of 2 A g-1, an excellent rate property of 68.6% capacity retention at 20 A g-1, and an 87.6% specific capacitance retention of its initial value after 7000 cycles at a high current density of 10 A g-1, superior to those of IH-Co3O4. Furthermore, an optimal asymmetric supercapacitor (ASC) was also constructed with IH-NiCo2O4 as the positive electrode and graphene as the negative electrode. The ASC delivers a high energy density of 39.4 Wh kg-1 at a power density of 800 W kg-1. Even at a high power density of 8000 W kg-1, the energy density still reaches 27.2 Wh kg-1. Moreover, the ASC shows a good cycling stability with 80.1% specific capacitance retention after 5000 cycles at 6 A g-1. The excellent electrochemical performance of IH-NiCo2O4 makes it a promising electrode material in energy storage field.

Rapid synthesis of rGO conjugated hierarchical NiCo2O4 hollow mesoporous nanospheres with enhanced glucose sensitivity

NiCo2O4 nanospheres, a type of conjugated reduced graphene oxide (rGO), are compounded by a simple and easy synthesis of Cu2O/GO and fabricated NiCo2O4/rGO nanocomposites based on a Cu2O/GO template. The structure and morphology of the hierarchical NiCo2O4/rGO are characterized by x-ray diffraction, x-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy. The electrochemistry properties of NiCo2O4/rGO composites toward glucose are determined based on a glassy carbon electrode, and the results indicate that the hollow nanospheres of NiCo2O4/rGO could achieve high-sensitivity detections of glucose. The NiCo2O4/rGO composite has a detection range of 0.04 mM to 1.28 mM, a sensitivity of 2082.57 μA mM−1 cm−2, and a detection limit of 0.7 μM. The composite further exhibits obvious stability, superior reproducibility, and excellent selectivity. This study demonstrates that NiCo2O4/rGO is a unique and material with high potential in glucose sensing.

Facile synthesis of hierarchical mesoporous NiCo2O4 nanoflowers with large specific surface area for high-performance supercapacitors

Hierarchical mesoporous NiCo2O4 nanoflowers with large specific surface area have been prepared through a simple, low cost and green method. The electrochemical performances of the NiCo2O4 electrode materials have been investigated, and the results show that NiCo2O4 electrode materials exhibit high specific capacitances of 1635F/g at 2A/g, low internal resistance ~0.24Ω, and remarkable long-term cycling stability, demonstrating its excellent electrochemical performances for supercapacitors. Such enhanced electrochemical performances and the facile synthetic method of NiCo2O4 electrode materials can offer great promise in next generation supercapacitor applications.

Inside Cover: Hierarchical NiCo2O4 Hollow Microcuboids as Bifunctional Electrocatalysts for Overall Water‐Splitting (Angew. Chem. Int. Ed. 21/2016)

Inside Cover: Hierarchical NiCo₂O₄ Hollow Microcuboids as Bifunctional Electrocatalysts for Overall Water‐Splitting (Angew. Chem. Int. Ed. 21/2016)

Hierarchical NiCo2O4 hollow nanospheres as high efficient bi-functional catalysts for oxygen reduction and evolution reactions

High efficient, cost-effective catalysts for both the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are the key issue of the rechargeable lithium-air batteries. Herein, we report the facile synthesis of hierarchical NiCo2O4 (NCO) hollow nanospheres via a hard template method and following heat treatment. The synthesized hollow NCO consists of ultrathin nanosheets, which could provide larger specific surface area, more active sites and easy access channels for oxygen and electrolyte transport. The electrochemical studies reveal that the NCO hollow owns excellent ORR and OER catalytic activities, characterized with lower onset potential, higher diffusion limiting current density. Moreover, the NCO hollow shows superior stability compared to that of NCO urchin, Pt/C and RuO2 for ORR and OER, respectively. The excellent electrocatalytic activities, long-term stability for both the ORR and OER and the facile synthesis procedure make the NCO hollow a potential promising bi-functional catalyst for the metal-air batteries and fuel cells.

High electrochemical performances of hierarchical hydrangea macrophylla like NiCo2O4 and NiCo2S4 as anode materials for Li-ion batteries

In this work, hierarchical hydrangea macrophylla like NiCo2O4 has been synthesized by solvothermal method followed by calcination treatment in air. By using Na2S as sulfur source, the NiCo2O4 is converted into NiCo2S4. Such hierarchical NiCo2O4 exhibits a high specific capacity and excellent cycling stability (928mAhg−1 at a current density of 100mAg−1 after 100 cycles). Even at high current density of 2000mAg−1, the electrode still delivers a specific capacity of 371mAhg−1 after 50 cycles. When the NiCo2S4 is used as anode materials for lithium-ion batteries, a high discharge capacity of 1204mAhg−1 can be achieved. Meanwhile, the NiCo2S4 electrode displays good cycling stability and rate capability. The excellent electrochemical performances can be attributed to the unique porous structure, which can effectively reduce the diffusion length for lithium ions and electrons, and alleviate volume expansion during the charge-discharge processes.

Hierarchical NiCo2 O4 Hollow Microcuboids as Bifunctional Electrocatalysts for Overall Water-Splitting.

Bifunctional electrocatalysts for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in alkaline electrolyte may improve the efficiency of overall water splitting. Nickel cobaltite (NiCo2 O4 ) has been considered a promising electrode material for the OER. However, NiCo2 O4 that can be used as an electrocatalyst in HER has not been studied yet. Herein, we report self-assembled hierarchical NiCo2 O4 hollow microcuboids for overall water splitting including both the HER and OER reactions. The NiCo2 O4 electrode shows excellent activity toward overall water splitting, with 10 mA cm(-2) water-splitting current reached by applying just 1.65 V and 20 mA cm(-2) by applying just 1.74 V across the two electrodes. The synthesis of NiCo2 O4 microflowers confirms the importance of structural features for high-performance overall water splitting.

Hierarchical NiCo2O4 Hollow Microcuboids as Bifunctional Electrocatalysts for Overall Water‐Splitting

AbstractBifunctional electrocatalysts for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in alkaline electrolyte may improve the efficiency of overall water splitting. Nickel cobaltite (NiCo2O4) has been considered a promising electrode material for the OER. However, NiCo2O4 that can be used as an electrocatalyst in HER has not been studied yet. Herein, we report self‐assembled hierarchical NiCo2O4 hollow microcuboids for overall water splitting including both the HER and OER reactions. The NiCo2O4 electrode shows excellent activity toward overall water splitting, with 10 mA cm−2 water‐splitting current reached by applying just 1.65 V and 20 mA cm−2 by applying just 1.74 V across the two electrodes. The synthesis of NiCo2O4 microflowers confirms the importance of structural features for high‐performance overall water splitting.

Hierarchical 3D NiCo2O4 nanoflowers as electrode materials for high performance supercapacitors

Three-dimensional NiCo2O4 nanoflowers have been directly grown on a stainless steel substrate surface, using a facile chemical bath deposition (CBD) technique. The deposited thin films were characterized for their structural, morphological and electrochemical properties by using XRD, SEM, cyclic voltammetry and charge discharge methods. The 3D NiCo2O4 nanoflowers were used as working electrode to measure the supercapacitor performance. The 3D NiCo2O4 nanoflowers exhibit high specific capacitance of 543 Fg−1 at current density 1 Ag−1. The capacitance loss was 9.4 % after 1000 cycles at a current density of 3 Ag−1. This shows a good cycle stability and high rate capability of 3D NiCo2O4 nanoflowers. From this investigation it can be concluded that the low cost and environmental friendly CBD technique could be used to deposit efficient 3D NiCo2O4 nanoflowers for supercapacitor application.

Superior performance of 3 D Co-Ni bimetallic oxides for catalytic degradation of organic dye: Investigation on the effect of catalyst morphology and catalytic mechanism

An application of novel magnetic separable NiCo2O4 in microwave-induced catalytic degradation (MICD) of organic dye was found, and the structures of NiCo2O4 significantly affect its catalytic activity. Diverse NiCo2O4 structures, including NiCo2O4 nanoplates (NiCo2O4-P), NiCo2O4 nanorods (NiCo2O4-R), NiCo2O4 nanoparticles (NiCo2O4-N) and three-dimensional (3D) hierarchical dandelion-like NiCo2O4 spheres (3D NiCo2O4-S), have been successfully synthesized. Among them, 3D NiCo2O4-S displayed superior catalytic activity for congo red (CR) under microwave (MW) irradiation. Enhanced catalytic activity of 3D NiCo2O4-S can be attributed to the higher MW energy harvesting capacity resulted from multiple absorption of MW and relatively high specific surface area. Various scavengers, the band structure, as well as Mott–Schottky analysis, were utilized to identify the roles of active species. A possible catalytic mechanism was proposed. The 3D NiCo2O4-S is expected to have potential applications in pollutants degradation because of its efficient catalysis, easy separation and good reusability.

Time and temperature dependent multiple hierarchical NiCo2O4 for high-performance supercapacitors.

A multiple hierarchical NiCo2O4 (denoted as P-100), which was constructed of nanosheets covered with nanowires, was obtained by a facial hydrothermal method in combination with annealing treatment at 300 °C. The hydrothermal temperature and reaction time play key roles in the formation of the unique hierarchical NiCo2O4 based on the morphology evolution. As a supercapacitor electrode material, the obtained P-100 displays a high specific capacitance of 1393 F g(-1) at 0.5 A g(-1). Furthermore, the assembled P-100//AC asymmetric supercapacitor demonstrates a high energy density (21.4 Wh kg(-1)) at a power density of 350 W kg(-1) and remarkable cycling stability. The good electrochemical performances of the P-100 are mainly due to its three dimensional hierarchical porous nanostructure and high specific surface area as well as the synergetic effect of the nanosheets and nanowires in NiCo2O4. The experimental results demonstrated that the multiple hierarchical NiCo2O4 is a promising electrode material for high-performance supercapacitors.

Template-free synthesis of 3D hierarchical nanostructured NiCo2O4mesoporous ultrathin nanosheet hollow microspheres for excellent methanol electrooxidation and supercapacitors

Novel 3D hierarchical NiCo2O4mesoporous ultrathin nanosheets hollow microspheres upon a facile template-free solvothermal method followed air-annealing shows excellent methanol electrooxidation and supercapacitors performance.