Fabrication of CuFe2O4@g-C3N4@GNPs nanocomposites as anode material for supercapacitor applications

The aim of this study was to synthesize CuFe₂O₄ together with g-C₃N₄ and GNPs in various combinations on the surface of Ni foam for use as anode materials in supercapacitors. The fabricated electrodes were investigated by XRD, FTIR, XPS, BET, SEM and TEM for content and by CV, GCD and EIS analysis for electrochemistry. The characterization results showed that CuFe₂O₄ was successfully synthesized together with g-C₃N₄ and GNPs in a nanosponge-like geometry. The highest value of specific capacitance was found to be 989 mF/cm² at 2 mA measurement in the triple combination. Moreover, the stability of this electrode was measured to be 70% after 1500 cycles at 16 mA, while the energy and power densities were calculated to be 27.8 mWh/cm² and 300 mW/cm², respectively. The EIS results show that the carbon-based component increased the Cs value by decreasing the charge transfer and diffusion resistances of the electrodes. Compared to its counterparts in the literature, its Cs value is quite high, but its stability is low, so it can be used in low-cycle 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.     

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.     

Binder-less fabrication,some surface studies,and enhanced electrochemical performance of Co,Cu-embedded MnO2 thin film electrodes for supercapacitor application

We report the fabrication of nanocystalline MnO₂ thin film-based electrode on a predeposited indium tin oxide (ITO) film on the glass substrate, using a binderless and simple two-electrode electrofabrication approach. Effects of Co and Cu incorporation on microstructural and electrochemical performance of the electrode were optimally and extensively investigated. The experimental results for the optimum fabrication conditions for Co@MnO₂ and Cu@MnO₂ and pure MnO₂ thin film-based electrode samples showed uniqueness in microstructural features, degrees of crystallinity and roughness, and high electrochemical energy storage performance. Co@MnO₂ film electrode exhibited remarkable specific capacitance (1068 Fg^-1) and areal capacity (25.78 mAh cm^?2) as against other electrode films (Cu@MnO₂ and pure MnO₂) which exhibited specific capacitances 837 and 438 F g^?1 and areal capacities 10.6 and 4.9 mAh cm^?2, respectively. Exceptional stabilities were also recorded for the composite samples (87.2% and 84.4% for Cu@MnO₂ and Co@MnO₂ thin film electrodes, respectively) against the pure MnO₂ film electrode sample (77.8%), after 2000 cycles. In addition, the short time constants (1.27 s and 1.31 s) were respectively realized for the fabricated Co@MnO₂ and Cu@MnO₂ electrode films as against the pure MnO₂ electrodes (4.35 s). These features observed in the composite electrode samples demonstrated an exhibition of faster ion response and higher rate capability by the samples. Moreover, the incorporation of Co into the MnO₂ electrode material relatively improved the supercapacitive activeness by enhancing the charge transition and transport.     

Promising electrode material of Fe3O4 nanoparticles decorated on V2O5 nanobelts for high-performance symmetric supercapacitors

Bundled V₂O₅ nanobelts decorated with Fe₃O₄ nanoparticles (F3V nanostructures) were successfully synthesized to develop a low-cost electrode material for energy storage applications. The synthesized samples were subjected to structural, morphological and electrochemical studies. The Fe₃O₄ nanoparticles decorated over bundled V₂O₅ nanobelts exhibited better electrochemical properties than the pristine Fe₃O₄ nanoparticles and V₂O₅ nanobelts. The electrochemical behavior of the fabricated electrodes was investigated in an electrolyte of 3 M KOH, demonstrated an exceptional specific capacity values of 750.1, 660.3, and 1519 F g^–1 for V₂O₅, Fe₃O₄, and F3V respectively at a current density of 15 A g^–1. The assembled F3V symmetric supercapacitor (SSC) device exhibited an excellent specific capacitance of 93 F g^–1 at a current density of 0.5 A g^–1, delivering energy and power densities of 13 Wh.kg^–1 and 1530 W kg^–1, respectively, and superior long-term cycling stability of ～84% capacity retention over 5000 galvanostatic charge–discharge cycles. These findings demonstrate the extraordinary electrochemical characteristics of the F3V nanostructures, indicating their potential use in energy storage applications.     

ZnCo2O4/CNT composite for efficient supercapacitor electrodes

Due to their combination of enhanced electrical conductivity and high-performance electron and ion transport channels, binary metal oxides with well-morphological optimized electrode materials have been attracted the greatest research attention for high-performance supercapacitor applications. An easy co-precipitation method is used to synthesize ZnCo₂O₄ nanoparticles using NaOH and Urea as precipitation agents. To facilitate electrical conductivity, suitable carbon material such as carbon nanotube (CNT) has been added to make a composite material. The three-electrode system was preferred for estimating specific capacitance of prepared material and optimally efficient ZnCo₂O₄/CNT electrode delivered a moderate 888 F/g capacitance at 1 A/g in 3 M KOH and after 5000 charge discharge cycles 94.72% of cycling stability retained at 5 A/g. This paper presents a little price and simple procedure for preparation of ZnCo₂O₄/CNT electrode that promotes creative sprit for energy storage applications.     

NiCo2O4 arrays nanostructures on nickel foam: Morphology control and application for pseudocapacitors

The design of electrode materials with desirable morphology is of great importance and challenge to fabricate high-performance supercapacitors. In this work, NiCo₂O₄ nanopetal, nanosheet, nanoneedle and nanorod arrays on nickel foam have been synthesized through a facile hydrothermal method. The morphologies of NiCo₂O₄ arrays can be easily controlled by adjusting the kinds of alkali source and the addition of NH₄F. The electrochemical results show that the NiCo₂O₄ nanoneedles electrode has the optimal electrochemical performance among four samples, demonstrating its promising application potential for high performance supercapacitors. This investigation about morphology control of NiCo₂O₄ electrode materials and the relationship between the morphologies and corresponding electrochemical performances provides strategies to enhance the performance of supercapacitor electrodes.     

Electrochemical behavior of CuO/rGO nanopellets for flexible supercapacitor,non-enzymatic glucose,and H2O2 sensing application

In the present article, graphene oxide (GO) sheets and monoclinic copper oxide (CuO) nanocrystals are connected with each other and result in the formation of CuO/rGO nanopellets, and these nanopellets synthesized using coprecipitation method. The nanopellet structured CuO/rGO composite on carbon cloth, which act as current collector exhibits specific capacitance of 188 F g^?1 at a current density of 0.2 A g^?1 and up to 96.3% capacity retention after 2000 charge-discharge cycles. It shows a maximum energy density of 7.32 Wh kg^?1 and power density of 53 W kg^?1. The glucose sensing characteristics of CuO/rGO nanopellet is investigated on carbon cloth and ITO substrate. It shows glucose sensitivity of 0.805 mA mM^?1 cm^?2 and 0.2982 mA mM^?1 cm^?2 for a bundle like structured CuO/rGO composite on carbon cloth and ITO substrate, respectively. Further H₂O₂ sensing is studied on ITO substrate, which manifests H₂O₂ sensitivity of 84.39 μA mM^?1 cm^?2. The results indicate that nanopellet structured CuO/rGO composite could be a promising electrode material for supercapacitor, glucose, and H₂O₂ sensor.     

MnO2 depositing on the surface of hollow porous carbon microspheres for supercapacitor application

A supercapacitor electrode material was synthesized by using hollow carbon spheres prepared via high temperature sintering of dopamine hydrochloride and subsequent coating with MnO₂. SEM, TEM and analysis of energy pattern were used to characterize the structure, morphology and elemental composition of the material, which proved that the material had a good hollow structure and uniform surface morphology, and that MnO₂ was successfully coated on the surface of the carbon material. Electrochemical characterization using charge-discharge cycles at constant current and other methods show that the prepared materials have good specific capacitance and cycle stability, and have a specific capacitance of 198 F.g^?1 at a current of 1 A·g^?1. When the charge and discharge cycle is carried out at 10 A·g^?1 for 5000 cycles, the capacitance remains stable at more than 180 F·g^?1.     

Conformal coatings of NiCo2O4 nanoparticles and nanosheets on carbon nanotubes for supercapacitor electrodes

NiCo₂O₄ is a promising electrode material for supercapacitors and it has been widely investigated. However, its low conductivity restricts the reaction kinetics. Combining it with carbon materials can efficiently overcome the issue. But, very limited research about the homogenous coatings of NiCo₂O₄ nanocrystals on carbon nanotubes (CNTs) is reported. In this work, thin nanosheets and small nanoparticles of NiCo₂O₄ densely coated on CNTs are synthesized by tuning the annealing time with a hybrid of metal hydroxide@CNTs as a precursor. In the precursor, core−shell structures are formed by conformally coating 2D metal hydroxides on CNTs. After annealing it at 300 °C for different time, NiCo₂O₄ nanosheets or nanoparticles are then obtained and the core−shell structure is remained. Due to the reduced crystal size of NiCo₂O₄ and the high conductivity of CNTs, the composites have large specific capacitances, excellent rate performances, and good stability. The composite of NiCo₂O₄ nanoparticles on CNTs has a higher specific capacitance, about 1786 F g⁻¹ at 0.5 A g⁻¹, than the hybrid of NiCo₂O₄ nanosheets on CNTs due to their different morphologies. Using the composite as positive electrode and activated carbon as negative electrode, a hybrid capacitor cell can work in a voltage of 1.6 V, delivering an energy density of 32.5 Wh kg⁻¹ at 800 W kg⁻¹, showing a large potential for supercapacitors.     

石墨烯/δ-MnO2复合材料的制备及其超级电容器性能

采用螯合法制备了RGO/δ-MnO₂复合材料,并用X射线粉末衍射（XRD）、低压氮气吸附脱附（BET）、X射线光电子能谱（XPS）、扫描电子显微镜（SEM）、透射电子显微镜（TEM）、能谱（EDS）、热重（TGA）对其结构和物相进行表征。采用循环伏安测试（CV）、恒电流充放电（GCD）以及循环测试对所制材料电化学储能进行测试。结果表明RGO/δ-MnO₂复合材料比纯石墨烯和纯δ-MnO₂具有更优异的电化学性能。当电流密度为1 A·g^-1时,RGO/δ-MnO₂复合材料的比电容可达322.6 F·g^-1,比纯δ-MnO₂电极材料高234.2 F·g^-1,比纯石墨烯高212.1 F·g^-1。当电流密度放大10倍后,RGO/δ-MnO₂复合材料的比电容保留率为79.1%。在1000次恒流充放电测试后,比电容为252 F·g^-1（99.6%）,说明该方法制备的RGO/δ-MnO₂复合材料是一种有应用前景的超级电容器电极材料。     

Controllable synthesis and magnetic properties of hydrothermally synthesized NiCo2O4 nano-spheres

In the work, we explored an efficient synthetic platform to purposefully fabricate different morphologies of NiCo₂O₄ by controlling the hydrothermal temperature. All the obtained samples were characterized by means of X-ray diffraction, scanning electron microscopy, high resolution transmission electron microscopy. With the increase of hydrothermal temperature, the morphology of obtained samples transformed from spongy nanosphere to ellipse-like, then to peanut-like structure and an effective blue shifting of Raman spectroscopy occurred. The magnetic measurements indicated that the materials transform from paramagnetic to weak ferromagnetic with the increase of hydrothermal temperature.     

Impact of temperature-induced oxygen vacancies in polyhedron MnFe2O4 nanoparticles: As excellent electrochemical sensor,supercapacitor and active photocatalyst

Here, we investigate the effect of temperature on solution combustion synthesized MnFe₂O₄ nanoparticles (NPs) as supercapacitor electrode material that would affect the structural, optical, electrochemical, magnetic and sensing properties. The variation in temperature influences the structure and morphology of synthesized NPs which in turn produces defect states in NPs. Powder X-ray diffraction studies confirms the presence of cubic spinel structure with increase in crystallinity and crystallite size with increase in temperature. Scanning electron microscopy analysis indicates the morphology change in NPs from spherical to network like interlinking to the formation of polyhedron structure at higher temperature. Photoluminescence, energy dispersive X-ray analysis, X-ray photoelectron scpectroscopy and UV-visible diffused reflectance spectroscopy studies emphasize the increase in surface oxygen vacancies concentration with narrowing of band gap from 2.9 to 2.5 eV. Electrochemical studies designate the excellent performance and desirable cyclic stability of synthesized NPs. In particular, the specific capacitance of synthesized NP increases with increase in temperature, reaching highest specific capacitance from CV was 297.7 F/g for 0.1 M HCl and 158.85 F/g for 0.1 M NaNO₃ electrolytes for NP synthesized at 500 °C. The synthesized NPs show excellent stability with high capacity retention in both the electrolytes. The graphite modified electrode can also sense Paracetamol and d-Glucose at a very low concentration of 1–5 mM. Meanwhile, it acts as a very good photocatalyst to decolourize Methylene Blue and Alizarin Red S dye under Sunlight illumination due to the increase in concentration of surface oxygen vacancies with narrow band gap. Finally, the synthesized MnFe₂O₄ NP can be used as a potential supercapacitor electrode with excellent stability and recyclability, to sense the analyte even at very low concentration and also act as a photocatalyst with high recyclability with the help of magnetic nature towards environmental cleaning.     

Synthesis and characterization of MnCo2O4 microspheres based air electrode for rechargeable sodium-air batteries

In this work, the nanosized porous MnCo₂O₄ microspheres were synthesized by a hydrothermal method and their electrochemical behaviors were investigated based on a carbon supported composite air electrode for rechargeable sodium-air batteries. Under dry air test condition, the MnCo₂O₄/C air electrode demonstrated a stable working voltage of around 2.1 V vs. Na⁺/Na and a high initial discharge capacity of 7709.4 mA h g⁻¹, based on the active material mass, at a current density of 0.1 mA cm⁻². By a limit on the depth of discharge, the cell exhibited a specific capacity of 1000 mA h g⁻¹ with a high cycling stability up to 130 cycles. The considerable electrocatalytic activity suggests that the as-proposed MnCo₂O₄ is a highly efficient catalyst as air electrode for rechargeable sodium-air batteries.     

R&D considerations for the performance and application of electrochemical capacitors

Research and development (R&D) of electrochemical capacitors is discussed in terms of material characteristics and device performance and testing. Various chemistries and technologies being developed are identified and the status of and problems associated with each of the technologies are discussed. The technologies considered include those using various types of carbon and pseudo-capacitive materials such as metal oxides. What is needed to make the various electrochemical capacitor technologies cost competitive with batteries for different applications and markets is also considered.Electrochemical capacitors (especially double-layer capacitors) are intrinsically high power devices of limited energy storage capability and long cycle life; batteries are basically energy storage devices, which can be designed and used as relatively high power devices with a sacrifice in useable energy storage capacity. Both electrochemical capacitors and high power batteries are designed with thin electrodes, materials having nano-scale characteristics, and a minimum resistance. Much of the research on electrochemical capacitors is concerned with increasing their energy density with the minimum sacrifice in power capability and cycle life for deep discharges. Of special interest has been the development of advanced carbons with specific capacitance (F/g) significantly greater than the present values of 150-200 F/g in aqueous electrolytes and 80-120 F/g in organic electrolytes. Cost continues to be a major obstacle to the development of large markets for electrochemical capacitors particularly for vehicle applications. The development of lower cost carbons appropriate for use in electrochemical capacitors is underway by several speciality carbon suppliers. The goal is to reduce the cost of the carbon to $10-15/kg.     

Nanoengineering of ZnCo2O4@CoMoO4 heterogeneous structures for supercapacitor and water splitting applications

A hybrid ZnCo₂O₄@CoMoO₄ heterogeneous structure deposited onto nickel foam was synthesized via a two-step hydrothermal process. The results demonstrate that the hybrid architecture exhibits excellent electrochemical performance, including the specific capacitance of 1040C g^?1 at 1 A g^?1 for hybrid structures, high energy density of 87.3 Wh kg^?1 at a power density of 2700 W kg^?1 for an as-assembled supercapacitor and excellent cycle stability with a capacity retention of 99% undergoing 8000 charge-discharge for the device. Moreover, it also shows favorable electrocatalytic activity with low overpotentials of 237 mV at 20 mA cm^?2 for oxygen evolution reaction and 114 mV at 10 mA cm^?2 for hydrogen evolution reaction, and low cell voltage of 1.54 V at 10 mA cm^?2 for overall water splitting. In addition, the stability maintains well for the long-term use of 13 h. We believe that this hybrid ZnCo₂O₄@CoMoO₄ heterogeneous structure could be a promising candidate for future energy storage and conversion.     

Novel and efficient hybrid supercapacitor of chemically synthesized quaternary 3D nanoflower-like NiCuCo2S4 electrode

In this work, we employed a simple and cost-effective chemical route to obtain a highly stable and efficient quaternary mesoporous 3D nanoflower-like NiCuCo₂S₄ nanocomposite for supercapacitor applications. The NiCuCo₂S₄ composite exhibited a mixture of NiCo₂S₄ and CuCo₂S₄ phases, confirming the formation a quaternary NiCuCo₂S₄ thin film. A surface morphological analysis revealed the unique nanoflower-like nanostructure of the annealed composite. The electrochemical analysis of the NiCuCo₂S₄ electrode demonstrated a high specific capacity (Cs) of 414 mAh g^?1 at a lower scan rate of 10 mV s^?1 and a superior cycling stability up to 3000 cycles. A solid-state hybrid supercapacitor (SHS) was also constructed by the NiCuCo₂S₄ and AC powder as positive and negative electrodes, respectively. The NiCuCo₂S₄//AC hybrid cell produced a high Cs, energy density, and power density of 159 F g^?1, 35.19 Wh kg^?1, and 0.66 kW kg^?1, respectively at a current density of 10 mA with good cycling stability. The results demonstrated that the fabrication process is effective for the development of a novel quaternary transition metal sulfide (TMS) electrode.     

NiCo2O4 nanosheets and nanocones as additive-free anodes for high-performance Li-ion batteries

Development of novel electrode materials with high energy and power densities for lithium-ion batteries (LIBs) is the key to meet the demands of electric vehicles. Transition metal oxides that can react with large amounts of Li⁺ for electrochemical energy storage are considered promising anode materials for LIBs. In this work, NiCo₂O₄ nanosheets and nanocones on Ni foam have been synthesized via general hydrothermal growth and low-temperature annealing treatment. They exhibit high rate capacities and good cyclic performance as LIB anodes owing to their architecture design, which reduces ion and electron transport distance, expands the electrode–electrolyte contact, increases the structural stability, and buffers volume change during cycles. Notably, NiCo₂O₄ nanosheets deliver an initial capacity of 2239 mAh g⁻¹ and a rate capacity of 964 mAh g⁻¹ at current densities of 100 and 5000 mA g⁻¹, respectively. The corresponding values of nanocones are 1912 and 714 mAh g⁻¹. Hence, the as-synthesized NiCo₂O₄ nanosheets and nanocones, which are carbon-free and binder-free with higher energy densities and stronger connections between active materials and current collectors for better stability, are promising for use in advanced anodes for high-performance LIBs.     

Novel binder-free electrode of NiCo2O4@NiMn2O4 core-shell arrays modified carbon fabric for enhanced electrochemical properties

There is still a great challenge to develop new-style battery-type electrode materials with low resistance, large surface area, and stable microstructures on carbon fabric, which limited the development of flexible devices. In this work, NiCo₂O₄ nanoneedle@NiMn₂O₄ nanosheet core-shell arrays are constructed on the carbon fabric as a high-capacitance and long-life supercapacitor electrode for the first time. Benefiting from this kind of binder-free core-shell microstructure, the CF@NiCo₂O₄@NiMn₂O₄ electrode displays extraordinary specific-capacitance of 539.2 F g⁻¹ at a current density of 2 A g⁻¹, and nearly 93.0% retention of total capacitance even after discharging 5000 cycles. The outstanding properties of the hybrid electrode demonstrate that it is of great potential for flexible supercapacitors and batteries the application.     

An exploration of 3-methoxypropionitrile chemical sensor based on layered hexagonal NiCo2O4 nanoplates as electrode material

Binary metal oxide, nickel-cobalt oxide (NiCo₂O₄), was hydrothermally synthesized for the successful utilization as electrochemical electrode in chemical sensor. Benefited from the large surface area, binary NiCo₂O₄ stacked hexagonal nanoplates (HNPs) based electrode was utilized for the electrochemical sensing application towards teratogenic chemical i.e. 3-methoxypropionitrile (3-MPN). The sensing results displayed a reproducible sensitivity of ~605 μAμM^?1cm^?2, detection limit of ~11.8 μM with the correlation coefficient (R) of ~0.99502 and good linearity from ~10 μM to ~100 μM. Stability and repeatability of binary NiCo₂O₄ stacked HNPs based electrode was investigated with satisfactory results. Our synthesized binary NiCo₂O₄ stacked HNPs based electrode is promising for sensor applications and thus, enlightens the possibility of synthesizing other binary oxide materials.