Urchin like NiCo2O4/rGO nanocomposite for high energy asymmetric storage applications

New attractive advances in electrode preparation for supercapacitor applications with rGO based composite materials are eye-catching attention of researchers. Cobalt oxide is considered as an effective electrode for full cell fabrication due to its high specific capacitance. Cost effective solvothermal method was used to prepare pristine Co₃O₄ nanorods, NiCo₂O₄ nanorods and NiCo₂O₄/rGO urchin like nanocilia structure composite materials. The complete electrochemical studies were used to check the obtained product electrochemical activity. The high specific capacitance values are obtained for NiCo₂O₄/rGO urchin like nanocilia composite electrode material which leads to design a full cell and make use as practical applications with illuminating red, green, blue LED source. The capacitive retention of 92.28% even after 5000 cycles achieved in GCD cyclic performance at a high current density implies its excellent stability.     

Enhancing the performance and stability of NiCo2O4 nanoneedle coated on Ni foam electrodes with Ni seed layer for supercapacitor applications

We introduce a facile way to improve the performance of NiCo₂O₄ electrode by including a Ni seed layer. The seed layer deposited on Ni foam electrode (NiCo₂O₄/Ni@NF) shows the superior specific capacity of 1142 C g⁻¹ at 1 A g⁻¹ with the excellent cycle stability of ∼96% even after 5000 cycles at a higher current density of 5 A g⁻¹. These values are about 3.7 times higher than that of the electrode (NiCo₂O₄@NF) without a seed layer, which shows the specific capacity of 305 C g⁻¹@1 A g⁻¹ with cycle stability of 84% even at a lower current density of 1 A g⁻¹. The enhanced performance of the NiCo₂O₄/Ni@NF electrode may be attributed to lower interface resistance, fast redox reversible reaction, and improved surface active sites. Further, the asymmetric solid-state supercapacitor device is fabricated by using the NiCo₂O₄/Ni@NF electrode as a positive and reduced graphene oxide (rGO)-Fe₂O₃ nanograin as a negative electrode with PVA-KOH gel electrolyte, and the NiCo₂O₄/Ni20@NF//rGO-Fe₂O₃@NF asymmetric solid state device delivers an areal capacitance of 446 mF cm⁻² with a low capacitance loss of 18% even after 10000 cycles. Further, the fabricated asymmetric solid state device shows a maximum energy density of 124.3 Wh cm⁻² (at 3.58 kW cm⁻²) and power density of 14.88 kW cm⁻² (at 31.41 Wh cm⁻²).     

Flower-like NiCo2O4/NiCo2S4 electrodes on Ni mesh for higher supercapacitor applications

In this research, we have effectively synthesized a novel NiCo₂O₄/NiCo₂S₄ powder by co-precipitation and thin films prepared using a screen-printing method on Ni mesh for supercapacitor applications. Herein, we report the effect of unique hierarchical nanostructures and the systematic effect of Ni and Co on the structural, morphological and electrical properties of the NiCo₂O₄/NiCo₂S₄ electrodes. The optimized NiCo₂O₄/NiCo₂S₄ electrode shows outstanding performance with a specific capacitance of 1966 F g⁻¹ at 5 mV s⁻¹. The cycling stability reports indicate the NiCo₂O₄/NiCo₂S₄ electrodes have an outstanding cyclic stability with 91% capacity retention. From the supercapacitor performance results, we confirmed that the NiCo₂O₄/NiCo₂S₄ electrode is useful for the fabrication of symmetric supercapacitors. These results reveal that the NiCo₂O₄/NiCo₂S₄ electrodes is a capable electrode material for supercapacitor applications in the future.     

Hydrothermal and soft-templating synthesis of mesoporous NiCo2O4 nanomaterials for high-performance electrochemical capacitors

Mesoporous nickel cobaltite (NiCo₂O₄) nanoparticles were synthesized via a hydrothermal and soft-templating method through quasi-reverse-micelle mechanism. The physicochemical properties of the NiCo₂O₄ materials were characterized via X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectra, and nitrogen sorption isotherms measurements. The electrochemical performances of the NiCo₂O₄ electrode were investigated by cyclic voltammetry, chronopotentiometry, and electrochemical impedance spectroscopy tests. The obtained NiCo₂O₄ materials exhibit typical mesoporous structures, with an average particle size of about 200 nm, a specific surface area of 88.63 m² g^?1, and a total pore volume of 0.337 cm³ g^?1. The facile electrolytes penetration for the mesoporous structures favors high-performance of the NiCo₂O₄ electrode. The NiCo₂O₄ electrode shows a high specific capacitance (591 F g^?1 at 1 A g^?1), high-rate capability (248 F g^?1 at 20 A g^?1), and a good cycling behavior for tested 3,000 cycles, indicating a promising application for electrochemical capacitors.     

Hierarchical mesoporous nickel cobaltite nanoneedle/carbon cloth arrays as superior flexible electrodes for supercapacitors

Hierarchical mesoporous NiCo₂O₄ nanoneedle arrays on carbon cloth have been fabricated by a simple hydrothermal approach combined with a post-annealing treatment. Such unique array nanoarchitectures exhibit remarkable electrochemical performance with high capacitance and desirable cycle life at high rates. When evaluated as an electrode material for supercapacitors, the NiCo₂O₄ nanoneedle arrays supported on carbon cloth was able to deliver high specific capacitance of 660 F g^-1 at current densities of 2 A g^-1 in 2 M KOH aqueous solution. In addition, the composite electrode shows excellent mechanical behavior and long-term cyclic stability (91.8% capacitance retention after 3,000 cycles). The fabrication method presented here is facile, cost-effective, and scalable, which may open a new pathway for real device applications.     

Amaryllis-like NiCo2S4 nanoflowers for high-performance flexible carbon-fiber-based solid-state supercapacitor

Low-cost dynamic materials for Faradaic redox reactions are needed for high-energy storage supercapacitors. A simple and cost-effective hydrothermal process was employed to synthesize amaryllis-like NiCo₂S₄ nanoflowers. The sample was characterized by X-ray powder diffraction, Brunauer–Emmett–Teller method, scanning electron microscopy, and transmission electron microscopy. NiCo₂S₄ nanoflowers were coated onto carbon fiber fabric and used as a binder-free electrode to fabricate a solid-state supercapacitor compact device. The solid-state supercapacitor exhibited excellent electrochemical performance, including high specific capacitance of 360 F g⁻¹ at scan rate of 5 mV s⁻¹ and high energy density of 25 W h kg⁻¹ at power density of 168 W kg⁻¹. In addition, the supercapacitor possessed high flexibility and good stability by retaining 90% capacitance after 5000 cycles. The high conductivity and Faradic-redox activity of NiCo₂S₄ nanoflowers resulted in high specific energy and power. Thus, NiCo₂S₄ nanoflowers are promising pseudocapacitive materials for low-cost and lightweight solid-state supercapacitors.     

Synthesis of 3D nanoflower-like mesoporous NiCo2O4 N-doped CNTs nanocomposite for solid-state hybrid supercapacitor; efficient material for the positive electrode

In this research work, we report a novel method for developing ternary NiCo₂O₄ compounds using deep eutectic solvents (DESs) and a strategy for improving their pseudocapacitive performance. NiCo₂O₄ composites with N-doped carbon nanotubes (NCNTs) were fabricated on Ni foam using a hydrothermal method. The electrochemical performance of the NiCo₂O₄ was altered with the change in the reaction temperature. The composite of NiCo₂O₄ and NCNTs demonstrated a maximum value of specific capacity of 303 mAh g⁻¹ at a scan rate of 5 mV s⁻¹. The specific capacity for the composite compound was 1.3-fold greater than that of the pristine NiCo₂O₄ sample. For practical applications, we constructed a flexible solid-state hybrid supercapacitor comprised of NiCo₂O₄/NCNTs//activated carbon (AC) cells with an excellent energy density of 12.31 Wh kg⁻¹, outstanding power density of 8.96 kW kg⁻¹, and tremendous electrode stability. The three-dimensional mesoporous nanoflowers and nanotubes-like nanostructures of NiCo₂O₄ are well-suited for use in hybrid devices as well as convenient for flexible electronic devices.     

Hierarchical porous NiCo2O4 nanomaterials with excellent cycling behavior for electrochemical capacitors via a hard-templating route

Hierarchical porous nickel cobaltite (NiCo₂O₄) nanomaterials were synthesized via a hard-templating route. The obtained materials consist of nanostructured cubic NiCo₂O₄ spinels and a spot of cubic NiO nanoparticles, and the materials display a typical hierarchical porous structure. The NiCo₂O₄ electrode displays quasireversible dynamics characteristics, mainly Faradaic capacitance behavior and capacitance relaxation feature. The NiCo₂O₄ electrode exhibits an excellent long cycling behavior with no capacitance decays during 5,000 cycles at a current density of 2?A?g^?1 in 1?M KOH electrolytes, and the NiCo₂O₄ electrode exhibits both high power and energy performances even after 5,000 cycles with respective value of 1,758?W?kg^?1 and 8.3?W?h?kg^?1 in 1?M KOH electrolytes, indicating that the NiCo₂O₄ nanomaterials are promising candidates for electrochemical capacitors.     

Spinel nickel cobaltite nanoflakes anchored multiwalled carbon nanotubes driven photocatalyst for highly efficient degradation of organic pollutants using natural sunlight irradiation

Natural sun light driven photocatalytic materials have received remarkable attention due to their imminent applications in environmental remediation and energy conversions. In this study, natural sun light driven hierarchal spinel nickel cobaltite nanoflakes (NiCo₂O₄) anchored multiwalled carbon nanotubes (MWCNTs) nanocomposite was synthesized by using simple chemical route. The structural, morphological and functional group of as-prepared NiCo₂O₄ anchored MWCNTs was studied by using X-ray diffractometry, field emission scanning electron microscopy and Fourier transform infrared spectroscopy. The UV–vis diffusive reflectance spectroscopy results demonstrated decrease in optical bandgap from 1.32 to 1.16eV compared with pristine spinel NiCo₂O₄ nanoflakes. MWCNTs anchored NiCo₂O₄ showed extremely good photocatalytic behavior and we verified 98% degradation of MB in 35 min under natural sun light. NiCo₂O₄ anchored MWCNTs also confirmed its excellent stability and reusability by retaining 96% of photocatalytic efficiency after 7 cycles of operation. Improved photocatalytic behavior of NiCo₂O₄ anchored MWCNTs nanocomposite in comparison to NiCo₂O₄ nanoflakes is mainly attributed to excellent electron storage ability of MWCNTs which made catalyst a great acceptor. Moreover, porous structure of MWCNTs not only provides large surface area with more active sites but also increases conductivity and decreases agglomerations on the surface of material which render e^-/h⁺ pair recombination. Overall, this work shed new light for the synthesis of NiCo₂O₄ anchored MWCNTs with enhanced photocatalytic properties.     

NiFe-NiFe2O4/rGO composites: Controlled preparation and superior lithium storage properties

Binary transition-metal oxides with spinel structure have great potential as advanced anode materials for lithium-ion batteries (LIBs). Herein, NiFe-NiFe₂O₄/ reduced graphene oxide (rGO) composites are obtained via a facile cyanometallic framework precursor strategy to improve the lithium storage performance of NiFe₂O₄. In the composites, NiFe-NiFe₂O₄ nanoparticles with adjustable mass ratios of NiFe₂O₄ to NiFe alloy are homogeneously deposited on rGO sheets. As anode material for LIBs, the optimized NiFe-NiFe₂O₄/rGO composite displays remarkably enhanced lithium storage performance with an initial specific capacity as high as 1362 mAh g⁻¹ at 0.1 A g⁻¹ and a decent capacity retention of ca. 80% after 130 cycles. Besides, the composite delivers a reversible capacity of 550 mAh g⁻¹ at 1 A g⁻¹ after 300 cycles. During the charge–discharge cycles, the aggregation of the NiFe-NiFe₂O₄ nanoparticles and the structural collapse of the electrode can be well alleviated by rGO sheets. Moreover, the conductivity of the electrode can be significantly improved by the well-conductive NiFe alloy and rGO sheets. All these contribute to the improved lithium storage performance of NiFe-NiFe₂O₄/rGO composites.     

In situ synthesis of integrated dodecahedron NiO/NiCo2O4 coupled with N-doped porous hollow carbon capsule for high-performance supercapacitors

NiO and NiCo₂O₄ exhibit excellent synergistic effects and broad application prospects in electrochemical applications. However, the apparent interfacial instability between NiO and NiCo₂O₄ limits ion transport kinetics, charge/ion transfer, and electrochemical stability. In response, we developed and designed an integrated dodecahedron NiO/NiCo₂O₄ by a facile in-situ calcination method. Moreover, by utilizing the porous hollow structure of nitrogen-doped carbon capsules (N-Cc) as a conductive network, the N-Cc_x@NiO/NiCo₂O₄ heterostructures with stable interface structure, excellent electrolyte adsorption, and electron transfer pathways were carefully designed. The N-Cc_1.0@NiO/NiCo₂O₄ heterostructures are found to deliver an outstanding specific capacitance of 658.8 F g⁻¹, and a high energy density of 101.40 Wh kg⁻¹ at a power density of 775.03 W kg⁻¹, along with capacitance retention of more than 93.5% after 8000 cycles. Based on the DFT calculations and electrochemical experimental results, this work provides an effective in situ route for the construction of high-performance metal oxide heterostructure electrode materials for new energy storage devices.     

Studies on synergetic effect of rGO-NiCo2S4 nanocomposite as an effective counter electrode material for DSSC

Nanocomposites of reduced graphene oxide (rGO) and NiCo₂S₄ with different amount of graphene oxide (GO) are synthesized through a one- step solvothermal method and their catalytic activity towards I^-/I₃^- redox electrolyte for dye-sensitized solar cell (DSSC) application are reported. The growth mechanism of the pristine hierarchical marigold like microspheres of NiCo₂S₄ that formed without rGO and the nanocomposite of rGO-NiCo₂S₄ are also proposed. Electrochemical studies confirmed the synergetic effect of nickel and cobalt ions with the high electrical conductive rGO networks that enhance the electrocatalytic activity of NiCo₂S₄ nanostructures. The synergistic effect between NiCo₂S₄ and rGO may be attributed to the higher conductivity of rGO and the inverse spinel crystal structure of NiCo₂S₄ that have more octahedral catalytic active sites of Co³⁺. The amount of graphene oxide plays the important role of controlling the DSSC performance and the power conversion efficiency. The efficiency achieved for the rGO-NiCo₂S₄ counter electrode (CE) based DSSC is 8.15%, which is remarkably higher than that of pristine NiCo₂S₄ (7.36%), and Pt (7.23%) under the same experimental conditions.     

Ni@NiCo2O4 core/shells composite as electrode material for supercapacitor

A novel Ni@NiCo₂O₄ core/shells structure consisting of the Ni microspheres skeletons and nanosheet-like NiCo₂O₄ skins was designed and investigated as the electrochemical electrode for supercapacitor. Due to the unique architecture with Ni microspheres as the highly conductive cores improving the electrical conductivity of electrode and external nanosheet-like NiCo₂O₄ shells as the efficient electrochemical active materials facilitating the contact between the electrode and electrolyte, the as-prepared Ni@NiCo₂O₄ exhibited excellent electrochemical performance with high specific capacity of 597 F g⁻¹ (1 A g⁻¹) as well as remarkable capacitance retention of 96% (3000 cycles). These impressive results pave the way to design high-performance electrode materials for energy storage.     

Materials and electrode designs of high-performance NiCo2S4/Reduced graphene oxide for supercapacitors

NiCo₂S₄ is one of the most promising bimetallic sulfides for use in energy-storage systems, but more studies are needed to endow NiCo₂S₄ with a high electrochemical reaction capability and reversibility. In this work, we present rationally materials design of an optimal NiCo₂S₄ nanoparticle in a reduced graphene oxide (RGO) matrix as a NiCo₂S₄/RGO nanocomposite. Furthermore, we report the improvements in the materials technology, demonstrating the NiCo₂S₄/RGO nanocomposite electrode with an excellent specific capacitance of 963–700 F g⁻¹ at 1–15 A g⁻¹, high capacitance retention of 70%, and long cycle life of 3000 cycles. The practical application is showcased in an asymmetric supercapacitor with a high active-material loading. The NiCo₂S₄/RGO nanocomposite shows a high energy density of 31 Wh kg⁻¹ at a power density of 987 W kg⁻¹ and maintains an excellent density of 23 Wh kg⁻¹ at a high power density of 7418 W kg⁻¹. The outstanding electrochemical utilization and stability of the NiCo₂S₄/RGO nanocomposite confirm that our systematic optimization in the materials science and technology in terms of the active-material synthesis, the electrode development, and the device design/fabrication would benefit the future development of high-performance supercapacitors.     

Structural rearrangement by Ni,Cr doping in zinc cobaltite and its influence on supercapacitance

Transitional metal oxides are prevalent in the energy storage devices due to their remarkable electrochemical activity and charge storage capability. In this study, a spinel structured zinc cobaltite (ZnCo₂O₄) is doped with Ni and Cr to form a novel (Ni,Cr:ZnCo₂O₄) electrode material towards supercapacitor (SC) applications. Dopants served as a conductivity booster, particle size reducer and active sites provider benefitting the electrochemical activity. Comparatively, the doped sample delivered a higher capacitance value of 575 Fg^-1 in the potential range of 0–0.6V with 1 M KOH solution as an electrolyte which is higher than that of the pristine material and better cyclic stability is improved from 82.2% to 90.24% for 2000 cycles. The specific capacitance value of 30 Fg^-1 and 73 Fg^-1 at 0.75 Ag^-1 is achieved for the fabricated asymmetric supercapacitor device with Ni,Cr:ZnCo₂O₄ using Cu foil and Ni foam as current collector respectively. The device assembled with doped sample using Ni foam current collector has an energy density of 16.3 WhKg^?1 and a power density of 0.9 KWKg^?1 superseding the performance of the devices constructed with the pristine ZnCo₂O_4. The performance of Ni and Cr doped spinel structured zinc cobaltite device indicates a notable progress towards the direction of better performance supercapacitor applications.     

Iron oxide supercapacitor of high volumetric energy and power density using binder-free supersonic spraying and self-healing rGO

Iron oxide (Fe₂O₃) nanoparticles and reduced graphene oxide (rGO) sheets were supersonically sprayed onto a nickel substrate to fabricate flexible supercapacitors. The supersonic impact velocity was adjusted by varying the air chamber pressure from 2 to 6 bar, which facilitated the self-healing of Stone-Wall defects in rGO sheets. Supersonic spraying caused exfoliation of the rGO sheets, which in turn increased the surface area and adherence of the Fe₂O₃ nanoparticles. The optimal case exhibited a specific capacitance of 1.44 F?cm^-2 at a current rate of 1.5 mA?cm^-2 and the energy density was 14.23 mWh?cm^-3 at 250 mW?cm^-3. The width of the potential window increased to 1.4 V, implying a significant increase in the energy storage capability. The energy density of the supersonically sprayed Fe₂O₃/rGO electrode also showed no signs of deterioration even when the increased current density interfered with the electrode performance.     

Preparation of scale-like nickel cobaltite nanosheets assembled on nitrogen-doped reduced graphene oxide for high-performance supercapacitors

Ultrathin scale-like nickel cobaltite (NiCo₂O₄) nanosheets supported on nitrogen-doped reduced graphene oxide (N-rGO) are successfully synthesized through a facile co-precipitation of Ni²⁺ and Co²⁺ in the presence of sodium citrate and hexamethylenetetramine and subsequent calcination treatment. The composition and morphology of NiCo₂O₄ nanosheets@nitrogen-doped reduced graphene oxide (denoted as NiCo₂O₄ NSs@N-rGO) were characterized by Scanning electron microscope, Transmission electron microscope, X-ray diffraction, Raman spectra, X-ray photoelectron spectroscopy, Brunauer–Emmett–Teller and thermogravimetric analysis. The thickness of NiCo₂O₄ nanosheets anchored on the reduced graphene oxide is around 4 nm. The capacitance of NiCo₂O₄ NSs@N-rGO is evaluated by cyclic voltammogram and galvanostatic charge/discharge with the result that the NiCo₂O₄ NSs@N-rGO could deliver a specific capacitance of 1540 F g⁻¹ after 1000 cycles at 10 A g⁻¹.     

Synthesis of In2O3/GNPs nanocomposites with integrated approaches to tune overall performance of electrochemical devices

The electroactive material with a porous structure, good electrical conductivity, hybrid composition, and a higher surface is considered more suitable for applications as an electrode in the energy storage device. Herein, we report the preparation of In₂O₃ nanoparticles via a simple chemical route and their nanocomposites with 10% (IOG-10), 30% (IOG-30), 50% (IOG-50), 70% (IOG-70), and 100% G-100 graphene nanoplatelets (GNPs) via ultra-sonication. The presence of GNPs in the nanocomposite samples was verified by powder X-ray diffraction (PXRD), Raman, and scanning electron microscopy (SEM) results. The prepared samples were loaded onto the porous 3D nickel foam (NF) substrate to manufacture the working electrode for electrochemical testing. The cyclic voltammetry (CV), as well as galvanostatic charge/discharge (GCD), results proposed the IOG-30@NF as a suitable electrode for electrochemical applications. More precisely, the IOG-30@NF electrode shows a specific capacitance of 1768 Fg^-1 at 1 Ag^-1, which is considerably higher than that of either G-100@NF or In₂O₃@NF electrodes. Besides, the IOG-30@NF electrode shows good cyclic stability of 92.2% after 4000 GCD tests completed at 12 Ag^-1. When increasing the current density value from 1 to 4, the IOG-30@NF electrode maintains a specific capability of 81%, ensuring its exceptional rate capability. The higher specific capacity, higher rate-performance, and better cyclic activity of the IOG-30@NF electrode can be ascribed to its hybrid-composition, nanoarchitecture In₂O₃, 3D but porous nickel foam substrate, appropriate graphene content, and interaction between In₂O₃ nanoparticles and GNPs nanosheets.     

Hierarchical 3D starfish-like Ni3S4–NiS on reduced graphene oxide for high-performance supercapacitors

In this research, Ni₃S₄–NiS with starfish morphology was synthesized with a simple hydrothermal method and then hybridized with reduced graphene oxide (rGO) as a material for high-performance supercapacitors. The crystal structure and morphology of the as-prepared materials were studied by X-ray diffraction spectroscopy and electron microscopy. Uniform distribution of Ni₃S₄–NiS on rGO was observed from electron microscopy images. The results showed that Ni₃S₄–NiS/rGO with a specific capacitance of 1578 Fg^-1 and discharge time of 603 s at the current density of 0.5 Ag^-1 has more capacity and stability relative to Ni₃S₄–NiS. The cyclic stability after 5000 cycles showed that the Ni₃S₄–NiS/rGO electrode is stable, and 91% of its corresponding initial capacitance retained at the end of 5000 cycles. The good results in capacitance and stability of this electrode can be regarded as an improvement for the development of highly efficient and economic supercapacitors for portable electronic devices.     

Sol–gel approach for controllable synthesis and electrochemical properties of NiCo2O4 crystals as electrode materials for application in supercapacitors

In this work, NiCo₂O₄ coral-like porous crystals, nanoparticles and submicron-sized particles have been systematically prepared via a facile sol–gel method, using citric acid as the chelating ligand and H₂O (H₂O-DMF) as solvent. The experimental results reveal that the initial molar concentration of reactants, reaction time and solvent species involved are crucial for preparing the target products. The as-obtained samples were characterized by means of XRPD, FESEM, HRTEM, EDS and SAED techniques. Finally, the electrochemical performances of NiCo₂O₄ crystals with distinct morphologies were evaluated by cyclic voltammetry, and galvanostatic charge–discharge cycling techniques. The results show that submicron-sized NiCo₂O₄ particles exhibit the best capacitive properties with high specific capacitance and excellent cycle stability. At a high mass loading (5.6 mg cm⁻²), specific capacitance value of submicron-sized NiCo₂O₄/Ni electrode reaches as much as 217 F g⁻¹, and 96.3% of which can be still maintained after 600 charge–discharge cycles. Therefore, NiCo₂O₄ crystal is very promising for real application in supercapacitors.