Temperature Dependent Synthesis of NiCo₂O₄ Nanostructures and Their Supercapacitor Performance: Morphological Transitions from Spherical to Flower-Like Structures

Temperature Dependent Synthesis of NiCo₂O₄ Nanostructures and Their Supercapacitor Performance: Morphological Transitions from Spherical to Flower-Like Structures | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Temperature Dependent Synthesis of NiCo₂O₄ Nanostructures and Their Supercapacitor Performance: Morphological Transitions from Spherical to Flower-Like Structures Suraj D. Pathan, Bismilla B. Mulla, Mahendra R. Waikul, Nanaji G. Durage This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8333957/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract In this paper, we searching the temperature dependant and temperature changing effect of the morphology of material, porosity and electrochemical performance of NiCo₂O₄ nanostructures synthesized material at 140°C, 160°C and 180°C for supercapacitor applications. With a temperature step wise rise, the obtained materials have clear morphological transformation starting from spherical nanoparticles to structures transferring to flower-like morphologies which are a type of grass over the sphere. These structural changes have definitely affected the material porosity and surface area, two major factors to enhance energy storage of supercapacitor performance. Electrochemical experiments such as electrochemical impedance, galvanostatic charge discharge and cyclic voltammetry reveal the optimum temperature for outstanding performance with regard to specific capacitance and cycle stability. The results show that the synthesis temperature regulation is a valid strategy for tuning the characteristics of NiCo₂O₄ toward high-performance energy storage. Symmetric super capacitor Nanomaterial Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Introduction With the desirable structural type and electrochemical action of metal oxides have received more attention as energy storge supercapacitor electrodes. The metal oxide could overcome the low capacity of carbon materials and avoid inferior cycle stability. In the past, pseudocapacitive materials such as Manganese Oxide (MnO₂), Cobalt Tetra oxide (Co3O4), Nickel Oxide (NiO), Vanadium Oxide (V2O5) and Molybdenum Trioxide (MoO3) were widely used because of their increasing specific capacitance and energy and power densities. The binary or ternary transition metal oxides due to their promising electrochemical performance and also increasing electrical conductivity have define the central area of energy storge research. When compared with single-metal oxides as seen in a study. The binary metal oxides like Nickel Cobaltite (NiCo2O4), Spinel Oxide of Cobalt Manganese (MnCo2O4), Spinel Copper Cobaltite (CuCo2O4) and Zinc Cobaltite (ZnCo2O4) originating from Co3O4 have demonstrated outstanding performance in supercapacitors. These materials will further promote the capabilities of supercapacitor technology due to their superior electrochemical attributes and conductivity. The electrochemical double layer capacitors (EDLCs) collect the charge through physical adsorption occurring at the electrode electrolyte interference. However, pseudo capacitors offer excellent energy storage through quick and reversible redox reaction processes on the surface of the electrode. The different materials are used in pseudo capacitors [ 7 – 8 ]. The charge separation occurs across a very short distance within an electrical double layer which forms at the boundary between an electrode and the adjacent electrolyte. Also, more charges can be accommodated on the large surface area of the electrodes. Which further augmented by a multitude of pores in a high surface area electrode material [ 9 ]. Due to these two major reasons the supercapacitor can store more energy. The electrode is the most crucial part of the supercapacitor and the selection of the material has a huge effect on the way the device functions. Thus, the development of the supercapacitor based on an aqueous metal oxide requires the careful selection of the electrode material, optimisation of the process and performance simulation. The statistical analysis and material characterisation can help solve such issues. The main factors that usually affect the selection of electrode materials include is; a high specific surface area, the addition of metal oxides, large pore size, the low internal resistance, low cost and less volume [ 10 ]. Transition metal oxides including MnO2, NiO, Co3O4, V2O5, RuO2 and MoO3 [26] are widely employed due to their significant specific capacitance, high power and energy densities. Due to their superior electrical and electrochemical performance compared to single metal oxides, binary or ternary transition metal oxides have been gaining popularity. Binary metal oxides such as NiCo2O4, MnCo2O4, CuCo2O4 and ZnCo2O4 are derived from the fundamental Co3O4 spinel structure [ 11 ]. Nickel cobaltite (NiCo2O4), with its transition metal oxide spinel structure has been of great interest for supercapacitors. Due to its low toxicity, low manufacturing costs, environmental friendliness, high electrical conductivity, superior redox properties and increased stability during electrochemical processes. As a result of the combined action of Ni and Co ions, which facilitate fast electron and ion movement under charge-storage conditions, NiCo2O4 shows better electrochemical performance than single-component oxides such as NiO or Co2O4. The presence of both Ni²⁺/Ni³⁺ and Co²⁺/Co³⁺ redox couples enhance the kinetic advantages of charge transfer and hence there is higher specific capacitance and a greater rate capability [ 12 – 13 ]. Even though these advantages exist, the shape, surface area and porosity of NiCo2O4 have a major impact on its electrochemical performance. In other words, in order to achieve a high charge storage capacity, nanostructure and morphology should be optimised so as to increase active surface area, reduce ion diffusion resistance and increase electrolyte accessibility [14–15]. In a recent literature a no studies were conducted on morphology modification of NiCo2O4. A variety of NiCo2O4 morphologies are obtained by different researchers like Urchin-like, nanoflowers, nanostructures, nanosheets and Nanoflakes [ 16 ] etc. Each one of the morphologies shows different electrochemical performance [ 17 ]. Recently, a two-stage hydrothermal process was used in the most recent work by Niraj et al. to produce binder-free, uniform one-dimensional (1D) structures of vanadium dioxide utilising a unique chemical procedure. The monoclinic phase of these VO2 nanostructures ranged in size from 10 to 100 nm in cross-sectional diameter. At a current density of 2 A g-1, it demonstrated an excellent specific capacity of 615.8C g-1 when tested in a three electrodes setup with 1M Na2SO4 electrolyte [ 18 ]. NiCo2O4 nanoflower thin films were successfully prepared by the chemical bath deposition process. The deposition temperature has a great influence on the shape of the resulting sample nanoflowers. The mature NiCo2O4 nanoflowers prepared at 363 K have a very high specific capacitance of 628 F/g at 5 mV/s [ 19 ]. The large-scale syntheses of urchinlike NiCo2O4 nanostructures by a simple hydrothermal process yielded NiCo2O4 urchins that had outstanding specific capacitance of 1650 and 1348 F g-1 at current densities of 1 and 15 A g-1 [ 19 ]. It is found that, the NiCo2O4 nanoflake array grown on Ni foam has a highly ordered structure with a large specific surface area providing a large quantity of reactive sites and facilitating the transportation of electrons and electrolyte ions. This leads to an enhanced specific capacitance of 854.7 F g-1 at 1 A g-1 and even maintained at 745.1 F g-1 at 10 A g-1 for the NiCo2O4 nanoflake array [ 20 – 21 ]. One step hydrothermal synthesis is an efficient technique in the preparation of a wide range of materials and chemical compounds in one reaction process. It involves the mixing of selected precursors in water and then heating the mixture inside a sealed high-pressure reactor usually a Teflon-lined stainless-steel autoclave. Under high temperature and pressure water acts as a highly reactive medium that enables controlled nucleation, crystal growth and structural evolution. Because of its simplicity, versatility and capability to produce materials with tunable structures this method has been widely adopted in materials science, nanotechnology and chemistry. By controlling reaction parameters such as temperature, pressure, pH, precursor ratio and reaction duration it allows the tuning of morphology, particle size, crystallinity and overall physicochemical properties of the synthesised products. These advantages make the one-step hydrothermal method particularly valuable for developing advanced nanomaterials with application specific functionalities. Hydrothermal synthesis is particularly favoured for the preparation of nanomaterials, including metal oxides, sulfides and composite structures. In general hydrothermal treatment involves the preparation of aqueous precursor solutions which are then transferred to a Teflon container placed inside an autoclave the latter is then heated inside an oven. During heating different stages of the reactions may appear in sequence such as nucleation, cluster formation, aggregation and crystallization due to increased temperature and autogenous pressure. Organic additives, surfactants and structure-directing agents often influence the final particle shape, degree of agglomeration and surface features. Several hydrothermal routes have been published over the years for the synthesis of nickel cobaltite (NiCo₂O₄) nanopowders enabling the control of morphology and optimization of properties for different applications. The main goals of the present study are; to synthesize the nanostructured NiCo₂O₄ by hydrothermal technique and systematically investigate their morphological variations. It helps us to evaluate how the reaction parameters like reaction time, temperature, precursor ratio and pH influence the structural and morphological features NiCo₂O₄ samples regarding specific capacitance, rate capability and long-term cyclic stability. Though several researchers report on the synthesis of NiCo₂O₄ the exact information about the influence of each synthesis parameter on morphology is still limited. Because the electrochemical performance of NiCo₂O₄ is strongly dependent on morphology one has to investigate the optimised synthesis conditions. This investigation covers the existing gaps in offering indepth insights into the hydrothermal approach and its potential to produce improved materials for renewable energy storage and environmental applications. Further the results can be used to develop next-generation electrode materials possessing superior performance and stability. Although much work has already illustrated the suitability of NiCo₂O₄ for high performance supercapacitors hydrothermal synthesis in particular offers better control over particle shape and size than more conventional solid state or high temperature combustion routes. Complementing the previous literature, the emphasis of the present work is thus on morphology optimization in NiCo₂O₄ structures through a soft chemical and solution-based approach. Reviewing the papers from 2001 up to the present it has been seen that a wide range of metal oxides of different morphologies have been synthesized by various chemical and physical methods. However better synthetic strategies must be developed continuously to tune morphology for their performance improvements. Between the years 2001 and 2005, the significant efforts were being directed toward the development of various metal oxide and polymer based electrode materials for energy storage applications. Various compositions, including PEO-KOH-H₂O polymer electrolytes, RuO₂·xH₂O/C composites, Mn₂O₃, SnO₂ xerogels, MnO₂, RuO₂ and RuO₂/CNT hybrids, were prepared through sol-gel processing, solution casting cathodic electrodeposition, electrochemical potential cycling and reduction-based chemical methods. Cyclic voltammetry, galvanostatic charge-discharge measurements and thermogravimetric analysis are some of the electrochemical studies conducted on these systems, showcasing attractive cycle efficiencies and capacitance values. Capacitive performances vary broadly generally between 90 to 720 F g-1 and up to 45 mF cm-2 and demonstrate early developments made in metal oxide based supercapacitor systems [ 23 – 31 ]. From 2006 to 2010, the field advanced further with the synthesis of materials such as polyaniline, metallic Ni, Co(OH)₂/CNT composites, RuO₂/CNT structures, single-walled carbon nanotubes (SWNTs), CrO₂, MnO₂/polypyrrole hybrids, graphite derivatives, Na₂Co₄- based compounds and RuCl₃·xH₂O. These materials were prepared through potentiodynamic deposition, general electrochemical deposition, cathodic methods, sol-gel synthesis, anodic techniques and precipitation routes. The resulting microstructures were highly varied, including spongy and porous textures, multi-walled tubular assemblies, spherical aggregates and mud cracked surface features. Electrochemical testing mainly cyclic voltammetry, galvanostatic charge discharge and thermal stability analysis demonstrated improvements in capacitive behavior, with reported values reaching as high as 785 F g-1. These findings confirmed the impact of controlled synthesis methodologies on enhancing electrochemical efficiency [ 32 – 38 ]. From 2011 to 2015, the investigations were increasingly focused on multicomponent and structurally engineered electrode materials. Typical synthesized compositions included Ni-Co alloys, NiCo₂, Ni₁/₃Co₁/₃Mn₁/₃(OH)₂, Ni-Co-Sn materials, NiCo₂O₄-rGO composites and NixCo₁-x(OH)₂. Representative synthesis methods in these works included the use of sol-gel routes, chemical reduction routes, Pechini methods, electrochemical approaches, precipitation, co-precipitation and template-free synthesis. The obtained morphologies were also highly varied, consisting of amorphous phases, nanowires, flower-like morphologies and highly porous structures. The corresponding electrochemical measurements continued to rely on cyclic voltammetry, galvanostatic charge discharge and thermogravimetric analysis. The life cycle of several materials was also extended to 5000 cycles. The capacitance values for this period have significantly increased, attaining a value as high as 2360 F g-1, reflecting major advances in morphological control and optimization of the material [ 30 – 43 ]. Within the period from 2016 to 2024, research was extended rapidly upon the development of advanced nanostructured and composite materials for high-performance energy storage. Materials synthesized include NiCo₂O₄, Zn-Ni-Co oxides, biomass-derived carbons such as glucose-based carbon, NiCo₂, NiCo₂S compounds and multifunctional composites like CFAC/Ni-Co and Ni(OH)₂/N-Co the approaches used for their synthesis were also getting highly sophisticated and varied comprising the low-temperature chemical approach, coprecipitation, microwave assisted routes, hydrothermal processing and various wet chemical approaches. The morphologies obtained included well defined nanostructures, hierarchical flower-like shapes, hollow spheres and dandelion inspired architectures. The electrochemical performance increased remarkably, with some materials exhibiting capacitance values of up to 2525 F g-1, showing remarkable progress in electrode design and fabrication for next-generation supercapacitors. The collective developments hence show the uninterrupted evolution of material science toward higher efficiency, tunable morphology and enhanced energy storage capabilities [44–53]. Experimental work Materials: Nickel nitrate hexahydrate (Ni(NO3)2·6H2O), Cobalt nitrate hexahydrate (Co(NO3)2·6H2O), Urea as a precipitating agent, Distilled water, Propanol, Glycerine. Synthesis: Ni/Co oxides were prepared by a facile hydrothermal synthesis method as described below. Firstly, a different molar ratio of nickel nitrate (Ni(NO3)2·6H2O) and cobalt nitrate (Co(NO3)2·6H2O) were dissolved in deionized (DI) water. Subsequently, certain amount of urea solution was slowly added dropwise into the above solution with vigorous stirring for 1 hour. After complete dissolution, the solution was transferred into a 100 ml Teflon lined autoclave and kept at 140°C for 6 hours. After reaction, the precipitate was collected and washed with deionised water and ethanol for several times. The obtained product was then dried in oven at 85°C for 12 hours and then calcined in air at 350°C step wise room temp to 350°C, 5°C for each minute and also next 2 hours to get the final sample. Then the product is obtained labelled as “NCO140”. For the comparison of different morphologies, the two other modified morphology material are synthesized by a using same precursors but different reaction condition i.e. varying the reaction conditions. The material synthesized at 160°C with the denoted as NCO160 while NCO180 is synthesized at 180°C. For a both material synthesis, the autoclave was kept for 6 hours at specified temperatures. The calcination and purification were carried out following the same process as similar for NCO140. Result and Discussion Material Characterization X-ray diffraction (XRD ) X-ray diffraction is a powerful analytical technique that is widely used to determine the crystallographic structure, phase composition, and structural integrity of material. In addition to confirming the crystal structure, XRD allows information on deviations from the ideal lattice due to internal stresses, strain and structural defects. Typically, such imperfections will manifest themselves as line broadening, shifting or change of intensity in the diffraction pattern, thereby allowing for evaluating microstructural characteristics. Due to its accuracy and reliability, XRD is a widely adopted technique in several fields, such as ceramics, metallurgy, pharmaceuticals, catalysis and energy storage. Therefore, it is also imperative for quality control because the presence of additional peaks in the diffractogram is indicative of secondary phases or impurities. The X-ray diffraction analysis confirms the characteristic spinel-type crystal structure of NiCo₂O₄, thereby indicating that the nickel and cobalt ions occupy both tetrahedral and octahedral lattice sites in mixed valence states. The typical XRD pattern exhibits sharp diffraction peaks, which are indexed to the planes {111}, {220}, {311}, {400} and {511}, matching the standard spinel NiCo₂O₄ reference data. The sharp and intense peaks indicate good crystallinity and the formation of a single-phase structure free from impurity phases. Estimation of the size of crystallites through the analysis of peak broadening with the Scherrer equation provides information on microstrain and lattice distortions that may become significant from peak characteristics. The lattice parameters are calculated and they will be very useful in understanding structural stability, defect chemistry and potential electronic behavior. Also, confirmation of phase purity was made by comparing the obtained pattern with the standard JCPDS data, hence ensuring the successful synthesis of NiCo₂O₄ with an expected spinel configuration. Fourier-transform infrared (FTIR) Fourier-transform infrared spectroscopy of nickel cobaltite provides important information about the vibrational properties of the material, thus helping the researchers understand the bonding environment and functional groups associated with its spinel structure. A typical FTIR spectrum of NiCo₂O₄ shows distinct absorption bands mainly due to the metal-oxygen (M-O) vibrations involving Ni²⁺ and Co³⁺ ions. The most important peaks appear in the low-wavenumber region, normally within 400-600cm⁻¹, representing the stretching vibration of metal-oxygen bonds in the spinel lattice. These bands are representative of the octahedral and tetrahedral coordination sites occupied by the metal ions. In some cases, extra broad features in the region of 1000-1300cm⁻¹ may also appear, which can arise from complex metal-oxygen interactions or residual surface groups formed during synthesis. The positions, shapes and intensities of these peaks reflect the symmetry and structural integrity of the spinel framework. By comparing the obtained FTIR spectrum with the standard reference data, it allows for confirmation of the successful formation of a spinel phase of NiCo₂O₄ and allows the detection of surface modifications, structural distortions or impurities introduced during its synthesis. Thus, FTIR becomes a valuable complementary technique to verify structural and chemical characteristics of NiCo₂O₄. Scanning Electron Microscopy (SEM): The morphology of the NiCo₂O₄ prepared at 180°C was investigated by using Scanning Electron Microscopy (SEM) and the results are represented in Fig. 3 (a-c). The SEM images reveal that, the sample is composed of uniform spherical nanoparticles with an average particle size of about 11.9nm. At high magnification, the particles have a rough surface with porosity, indicating the presence of interconnected pores throughout the structure. This kind of porosity is beneficial for electrochemical applications in supercapacitors and electrocatalysis since it maximises the surface area and allows faster ion transportation during charge discharge processes. The SEM micrographs taken within the range of magnifications from 50,000X to the nanometre scale up to the 1000 nm view clearly show the hierarchical features of this material. In addition to the spherical nanoparticles, the NiCo₂O₄ sample also exhibited nanoflower-like morphologies where the structures seem to self-assemble in flower-shaped clusters with diameters varying from ca. 5 µm up to 50 µm. This kind of combination of nanoscale spheres and microscale flower-like architecture implies an effective growth mechanism favourable to improve electrochemical performance by giving rise to a high degree of surface accessibility and structural stability. Energy Dispersive X-ray (EDAX) The EDAX analysis of the synthesised NiCo₂O₄ was performed to determine its elemental composition and confirm the stoichiometric ratio of the mixed metal oxide. The atomic ratio between nickel and cobalt has been confirmed to be approximately 1:2 with the appearance of well-defined characteristic X-ray peaks such as the Ni Kα peak at about 7.78 keV and the Co Kα peak at about 7.01 keV. Oxygen is part of the basic oxide lattice component, direct EDAX detection has a limitation due to the low atomic number. Hence the presence of oxygen can be inferred from the structural composition and the overall stoichiometric balance. No additional peak obviously signifies the absence of impurities or unwanted elemental contamination in the sample. This suggests successful synthesis with high purity. Further confirmation of elemental mapping also proved that Ni and Co were distributed quite homogeneously across the entire sample, reflecting good homogeneity in the material. These are particularly important in order for the material to be used in supercapacitors, electrocatalysis and other energy storage devices where performance strongly relies on the correct elemental ratio and appropriate distribution of its active components. X-ray Photoelectron Spectroscopy (XPS) The XPS analysis further confirms the successful formation of pure spinel NiCo₂O₄ without any impurities detectable by this technique. Only nickel, cobalt and oxygen elements could be identified from the survey spectrum, which confirms that high chemical purity is realised from this 180°C synthesised sample. The two major spin-orbit peaks in the Ni 2p spectrum occur at binding energies of ~ 855.6 eV (Ni 2p₃/₂) and ~ 873.2 eV (Ni 2p₁/₂) respectively with well-defined satellite peaks. These features indicate the coexistence of mixed oxidation states Ni²⁺ and Ni³⁺, a characteristic feature of inverse spinel structures that enhances electronic conductivity and therefore promotes fast redox reactions. Similarly, the Co 2p spectrum displays strong peaks at about 780.4 eV (Co 2p₃/₂) and 795.6 eV (Co 2p₁/₂), which confirm the existence of both Co²⁺ and Co³⁺ cations within the host lattice. The shake-up satellite peaks associated with these further supports the mixed valency nature of cobalt, which plays a crucial role in enhancing charge-transfer kinetics in electrochemical systems. The major peak at approximately 529.3 eV in the O 1s spectrum is assigned to lattice oxygen (O 2− ). The additional peaks at higher binding energy in the region of 531.0-532.0 eV are ascribed to surface hydroxyl groups and adsorbed oxygen species. Such surface oxygen states enhance the electrochemical activity due to the promotion of surface redox behavior and the improvement of wettability. The presence of mixed oxidation states of Ni and Co atoms, demonstrates strong electronic interactions within the spinel. Enhanced redox activity and enhanced electronic conductivity make NiCo₂O₄ synthesized at 180°C an extremely promising material for supercapacitors, batteries, electrocatalysis and other energy-storage applications. Brunauer Emmett Teller (BET) The mesoporous characteristic of NiCo₂O₄ prepared at 180°C was further verified by BET surface area analysis, showing a representative Type IV nitrogen adsorption-desorption isotherm with a well defined H₃ type hysteresis loop. The results reveal relatively high specific surface areas, indicating plenty of active sites and interconnected pore channels that would facilitate charge storage and ion transport in electrochemical applications. Moreover, Barrett Joyner Halenda (BJH) pore size distribution analysis shows the material has an average diameter of ca. 10–15 nm, and the majority of pores fall into the mesoporous range of 2–50 nm. Such a mesoporous architecture facilitates the diffusion of electrolyte ions in the whole electrode material, increases ion accessibility to active sites and thus leads to excellent electrochemical performances in supercapacitors and batteries. The isotherm features a hysteresis loop in the desorption branch at higher relative pressures, indicating capillary condensation in mesopores, while the adsorption branch reveals a gradual increase in the volume of adsorbed nitrogen at low relative pressures, corresponding to the monolayer-multilayer adsorption of nitrogen on pore walls. With its large surface area and porous texture that enhance electrochemical performance by facilitating redox reactions at the electrode-electrolyte interface and enabling efficient ion transport, NiCo₂O₄ is a promising material for supercapacitor and catalytic applications Electrochemical study In order to test the capacitive behaviour CV, galvanostatic charge-discharge and EIS will be used. Cyclic voltammetry is probably the single most popular experimental technique used by the electrochemist. Despite this popularity, many users receive little formal training in this technique. Galvanostatic Charge Discharge (GCD) tests or Constant Current Charging/Discharging are often employed to evaluate energy storage systems and materials, including those involved in electrochemical capacitors. So, an electroanalytical experiment used to study the electrochemical properties of an electroactive species in solution or adsorbed on an electrode surface. Electrochemical impedance spectroscopy provides kinetic and mechanistic data on a wide variety of electrochemical systems and hence finds broad use in such areas as corrosion studies, semiconductor science, energy conversion and storage technology, chemical sensing and biosensing, noninvasively diagnostics, so an electroanalytical experiment used to study the electrochemical properties of an electroactive species in solution or adsorbed on an electrode surface. Cyclic voltammetry(CV) The capacitive performance of NiCo₂O₄ was further investigated by CV in the potential window between 0 and 0.5V. In the following, the effect of the scan rate on the redox response was systematically studied by varying the scan rate from 5 to 100 mV/s. With increasing scan rate, both the anodic and cathodic peak currents increased proportionally, representing a typical diffusion-controlled process and good electrochemical reversibility. Current responses approximately range from 0.2 A to 0.4 A with slight broadening of the peaks at higher scan rates that can be ascribed to polarization and ohmic effects in the electrode material The capacitance values were integrated from the areas under the CV curves and showed the expected trend, varying with scan rate 512 F/g at 5 mV/s, 410 F/g at 20 mV/s, 328 F/g at 50 mV/s, 280 F/g at 80 mV/s and 250 F/g at 100 mV/s. Such a decrease in capacitance with scan rate increase is normal for pseudocapacitive materials, since higher scan rates reduce the time for which electrolyte ions can diffuse deeper into the porous structure. These results thus indicate very good capacitive behaviour of NiCo₂O₄ and its potential as an electrode material in supercapacitors. Galvanostatic charge-discharge (GCD) Galvanostatic charge-discharge measurements of NiCo₂O₄ were conducted in a potential window between 0.0 and 0.5 V with time recorded from 2 to 18 seconds. The GCD curves obtained display almost symmetrical charge and discharge profiles, revealing excellent reversibility with stable electrochemical behaviour. Charge-discharge segments demonstrate mostly linear and triangular profiles, which are very typical for pseudocapacitive materials. A slight deviation from perfect linearity is seen accordingly, it could be understood that Faradaic redox reactions make a significant contribution to the charge storage mechanism as a whole. Charging starts from about 0.0 V and proceeds to 0.5 V, while it discharges symmetrically back to the initial potential, proving good coulombic efficiency. The total time for charge and discharge is roughly 20 seconds indicating moderate current density and good energy storage behaviour. These observations prove that NiCo₂O₄ possesses both high reversibility and stable electrochemical performance, making it one of the most promising electrode materials for supercapacitor applications. Electrochemical Impedance Spectroscopy (EIS) EIS was used to investigate the charge-transfer resistance and ion diffusion behaviour of NiCo₂O₄, so as to gain insight into its suitability as an efficient electrode material. The Nyquist plot of this material generally shows a semicircular arc in the high-frequency region due to the charge-transfer resistance, R ct at the interface between the electrode and electrolyte. In the low-frequency region, there is a nearly linear segment, which is characteristic of Warburg impedance reflecting ion diffusion in the electrode. The fairly small R ct value indicates an enhancement in electrical conductivity. It also shows the, fast chargetransfer kinetics, which are necessary for high-performance electrochemical applications. Furthermore, the slope of the Warburg region indicates efficient ion transport through the mesoporous electrode structure. A combination of these features-low charge-transfer resistance and effective ion diffusion-also permits NiCo₂O₄ to have appropriate synergistic electronic and ionic transport properties, desirable for superior performance in supercapacitors and battery electrodes among other energy storage devices. Conclusion The present study depicted NiCo₂O₄ as a highly promising electrode material for supercapacitor applications owing to its excellent structural and electrochemical properties. Structural characterization using XRD confirmed the formation of a pure spinel phase, while FTIR analysis validated the presence of characteristic metal-oxygen vibrations within the lattice. The SEM investigations further revealed the uniform spherical nanoparticles and nanoflower-like architectures with a porous and rough surface, which provides a high surface area and interconnected channels. EDAX analysis confirmed the stoichiometric composition and homogeneous distribution of Ni and Co. XPS verified the coexistence of mixed oxidation states such as Ni²⁺/Ni³⁺ and Co²⁺/Co³⁺ and the presence of lattice oxygen and surface hydroxyl groups. BET studies further revealed a mesoporous structure with pore diameters in the 10–15 nm range, which facilitates rapid ion diffusion and enhances electrolyte accessibility. Electrochemical characterisation showed that NiCo₂O₄ exhibited excellent performance as a pseudocapacitive material. Cyclic voltammetry exhibited high values of specific capacitance, amounting to 512 F/g at 5 mV/s, decreasing moderately at higher scan rates, which is indicative of diffusion-limited ion transport at elevated rates. The GCD curves showed almost symmetrical triangular shapes, indicating high reversibility with good coulombic efficiency and stable energy storage behaviour. EIS further showed low chargetransfer resistance and efficient ion diffusion within the electrode, supporting rapid redox kinetics and superior electronic and ionic transport properties. Tailored morphology, high surface area, mixed oxidation states and mesoporous architecture allow NiCo₂O₄ to achieve superior electrochemical performance, making it a promising candidate for high-performance supercapacitors. The synthesis route should be further optimized by methods such as hydrothermal, sol-gel and co-precipitation, along with designing advanced NiCo₂O₄ based composites in order to further enhance electrical conductivity, surface area and stability during long term operation. This development will unlock the full potential of NiCo₂O₄ for next generation energy storage applications, while enabling efficient, cost-effective and sustainable supercapacitor technology. Declarations Author Contribution all other other guided me for this work Acknowledgement I would like to express my sincere gratitude to all the institutions and individuals who supported me throughout the completion of my work. I am deeply thankful to DKASC College, Ichalkaranji, YC College, Satara, DY Patil University, Kolhapur, Shivaji University, Kolhapur, and Mumbai University, Mumbai for their valuable guidance, facilities, and encouragement. Their support has played a significant role in the successful completion of this work References Yan SX, Luo SH, Sun MZ, Wang Q, Zhang YH, Liu X. Facile hydrothermal synthesis of urchin-like NiCo2O4 as advanced electrochemical pseudocapacitor materials. Int J Energy Res. 2021;45(14):20186–98. 10.1002/er.7101 . Karthikeyan S, Narenthiran B, Sivanantham A, Bhatlu LD, Maridurai T, Supercapacitor. Evolution and review. 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Flower-like nickel–cobalt oxide decorated dopamine-derived carbon nanocomposite for high performance supercapacitor applications. ACS Sustainable Chemistry & Enginee Additional Declarations No competing interests reported. Supplementary Files Allfiles.pptx table.docx Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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06:55:29","extension":"html","order_by":34,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":132937,"visible":true,"origin":"","legend":"","description":"","filename":"earlyproof.html","url":"https://assets-eu.researchsquare.com/files/rs-8333957/v1/b490c0c531f0366e1f69600e.html"},{"id":98196730,"identity":"a5788003-5bcf-4ce9-9451-3de0b157ab4a","added_by":"auto","created_at":"2025-12-15 06:55:28","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":33508,"visible":true,"origin":"","legend":"\u003cp\u003eXRD of NiCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e of NCO140, NCO160,NCO180\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-8333957/v1/59dcb3b890fb963660d3ba3c.png"},{"id":98196734,"identity":"7afa68a0-eabd-487c-9232-262ae2c6ef7c","added_by":"auto","created_at":"2025-12-15 06:55:29","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":51683,"visible":true,"origin":"","legend":"\u003cp\u003eNiCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e FT-IR of NCO180 (180°C).\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-8333957/v1/56acc257abd5fa5e0f8680f8.png"},{"id":98196713,"identity":"f2eb08be-ee04-4a37-9c21-a13730e91caf","added_by":"auto","created_at":"2025-12-15 06:55:27","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":643406,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003e(NCO140)-(NCO180): \u003c/strong\u003eSEM images of synthesized NiCo2O4 sample.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-8333957/v1/16aa35f29e39e128d4b29e36.png"},{"id":98196722,"identity":"9f54fceb-9074-40d9-ad52-d0873e4ed3da","added_by":"auto","created_at":"2025-12-15 06:55:27","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":111376,"visible":true,"origin":"","legend":"\u003cp\u003eNiCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e EDAX of NCO180 (180°C).\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-8333957/v1/fa2c42200283096ae1d9d127.png"},{"id":98196735,"identity":"b2b029b0-0768-420b-9086-6bc4588feec9","added_by":"auto","created_at":"2025-12-15 06:55:29","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":105449,"visible":true,"origin":"","legend":"\u003cp\u003eNiCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e XPS of NCO180 (180°C).\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-8333957/v1/6d1270b431022a7452518182.png"},{"id":98432055,"identity":"e76519b5-95c5-4707-8a06-e99542500032","added_by":"auto","created_at":"2025-12-17 16:48:53","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":39741,"visible":true,"origin":"","legend":"\u003cp\u003eNiCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4 \u003c/sub\u003eAdsorption desorption isotherm (180°C\u003csub\u003e).\u003c/sub\u003e\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-8333957/v1/3446f0d99c8298b7b85782aa.png"},{"id":98432569,"identity":"77f22881-0cf2-49fc-85c4-43bda7c398d2","added_by":"auto","created_at":"2025-12-17 16:49:42","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":39435,"visible":true,"origin":"","legend":"\u003cp\u003eNiCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e BET (180°C).\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-8333957/v1/30c5a0e7071698dc92c0f297.png"},{"id":98196750,"identity":"c61658bf-7cd7-499f-880c-f6f08bf1d761","added_by":"auto","created_at":"2025-12-15 06:55:35","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":31483,"visible":true,"origin":"","legend":"\u003cp\u003eNiCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e BJH (180°C)..\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-8333957/v1/fe846cab37c7986a886e79fd.png"},{"id":98196740,"identity":"3d85c3ae-00d5-4b98-b4f7-70894b90c4ad","added_by":"auto","created_at":"2025-12-15 06:55:29","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":57337,"visible":true,"origin":"","legend":"\u003cp\u003eNiCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e CV (180°C).\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-8333957/v1/fcd75d14c8871602ed534f41.png"},{"id":98196747,"identity":"122ff0d0-d245-449e-b429-becf1a85e05f","added_by":"auto","created_at":"2025-12-15 06:55:29","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":46542,"visible":true,"origin":"","legend":"\u003cp\u003eNiCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e CD (180°C).\u003c/p\u003e","description":"","filename":"10.png","url":"https://assets-eu.researchsquare.com/files/rs-8333957/v1/b1beb5adf59078276a4a69ad.png"},{"id":98196723,"identity":"bdc7a0f4-dddb-4492-8fce-6c5caaf21663","added_by":"auto","created_at":"2025-12-15 06:55:27","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":55772,"visible":true,"origin":"","legend":"\u003cp\u003eNiCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e EIS (180°C).\u003c/p\u003e","description":"","filename":"11.png","url":"https://assets-eu.researchsquare.com/files/rs-8333957/v1/1509eb18e528635cb96b5de0.png"},{"id":101943669,"identity":"c9c13a4c-c9f8-44ad-bce5-057012ae828b","added_by":"auto","created_at":"2026-02-05 09:42:46","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1753857,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8333957/v1/ee4ae297-b089-4187-abfc-aa7e7ade481a.pdf"},{"id":98196727,"identity":"6e134713-2d26-4ed6-844c-69932719007c","added_by":"auto","created_at":"2025-12-15 06:55:28","extension":"pptx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":4474162,"visible":true,"origin":"","legend":"","description":"","filename":"Allfiles.pptx","url":"https://assets-eu.researchsquare.com/files/rs-8333957/v1/8cfee41daa7e662e348b9902.pptx"},{"id":98196671,"identity":"07210a02-308f-4a3c-90a7-4c72dc2a48c6","added_by":"auto","created_at":"2025-12-15 06:55:21","extension":"docx","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":24280,"visible":true,"origin":"","legend":"","description":"","filename":"table.docx","url":"https://assets-eu.researchsquare.com/files/rs-8333957/v1/6e2d43515a3e20e79aababaf.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Temperature Dependent Synthesis of NiCo₂O₄ Nanostructures and Their Supercapacitor Performance: Morphological Transitions from Spherical to Flower-Like Structures","fulltext":[{"header":"Introduction","content":"\u003cp\u003eWith the desirable structural type and electrochemical action of metal oxides have received more attention as energy storge supercapacitor electrodes. The metal oxide could overcome the low capacity of carbon materials and avoid inferior cycle stability. In the past, pseudocapacitive materials such as Manganese Oxide (MnO₂), Cobalt Tetra oxide (Co3O4), Nickel Oxide (NiO), Vanadium Oxide (V2O5) and Molybdenum Trioxide (MoO3) were widely used because of their increasing specific capacitance and energy and power densities.\u003c/p\u003e \u003cp\u003eThe binary or ternary transition metal oxides due to their promising electrochemical performance and also increasing electrical conductivity have define the central area of energy storge research. When compared with single-metal oxides as seen in a study. The binary metal oxides like Nickel Cobaltite (NiCo2O4), Spinel Oxide of Cobalt Manganese (MnCo2O4), Spinel Copper Cobaltite (CuCo2O4) and Zinc Cobaltite (ZnCo2O4) originating from Co3O4 have demonstrated outstanding performance in supercapacitors. These materials will further promote the capabilities of supercapacitor technology due to their superior electrochemical attributes and conductivity.\u003c/p\u003e \u003cp\u003eThe electrochemical double layer capacitors (EDLCs) collect the charge through physical adsorption occurring at the electrode electrolyte interference. However, pseudo capacitors offer excellent energy storage through quick and reversible redox reaction processes on the surface of the electrode. The different materials are used in pseudo capacitors [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe charge separation occurs across a very short distance within an electrical double layer which forms at the boundary between an electrode and the adjacent electrolyte. Also, more charges can be accommodated on the large surface area of the electrodes. Which further augmented by a multitude of pores in a high surface area electrode material [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. Due to these two major reasons the supercapacitor can store more energy.\u003c/p\u003e \u003cp\u003eThe electrode is the most crucial part of the supercapacitor and the selection of the material has a huge effect on the way the device functions. Thus, the development of the supercapacitor based on an aqueous metal oxide requires the careful selection of the electrode material, optimisation of the process and performance simulation. The statistical analysis and material characterisation can help solve such issues. The main factors that usually affect the selection of electrode materials include is; a high specific surface area, the addition of metal oxides, large pore size, the low internal resistance, low cost and less volume [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eTransition metal oxides including MnO2, NiO, Co3O4, V2O5, RuO2 and MoO3 [26] are widely employed due to their significant specific capacitance, high power and energy\u003c/p\u003e \u003cp\u003edensities. Due to their superior electrical and electrochemical performance compared to single metal oxides, binary or ternary transition metal oxides have been gaining popularity. Binary metal oxides such as NiCo2O4, MnCo2O4, CuCo2O4 and ZnCo2O4 are derived from the fundamental Co3O4 spinel structure [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eNickel cobaltite (NiCo2O4), with its transition metal oxide spinel structure has been of great interest for supercapacitors. Due to its low toxicity, low manufacturing costs, environmental friendliness, high electrical conductivity, superior redox properties and increased stability during electrochemical processes. As a result of the combined action of Ni and Co ions, which facilitate fast electron and ion movement under charge-storage conditions, NiCo2O4 shows better electrochemical performance than single-component oxides such as NiO or Co2O4. The presence of both Ni\u0026sup2;⁺/Ni\u0026sup3;⁺ and Co\u0026sup2;⁺/Co\u0026sup3;⁺ redox couples enhance the kinetic advantages of charge transfer and hence there is higher specific capacitance and a greater rate capability [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. Even though these advantages exist, the shape, surface area and porosity of NiCo2O4 have a major impact on its electrochemical performance. In other words, in order to achieve a high charge storage capacity, nanostructure and morphology should be optimised so as to increase active surface area, reduce ion diffusion resistance and increase electrolyte accessibility [14\u0026ndash;15].\u003c/p\u003e \u003cp\u003eIn a recent literature a no studies were conducted on morphology modification of NiCo2O4. A variety of NiCo2O4 morphologies are obtained by different researchers like Urchin-like, nanoflowers, nanostructures, nanosheets and Nanoflakes [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e16\u003c/span\u003e] etc. Each one of the morphologies shows different electrochemical performance [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. Recently, a two-stage hydrothermal process was used in the most recent work by Niraj et al. to produce binder-free, uniform one-dimensional (1D) structures of vanadium dioxide utilising a unique chemical procedure. The monoclinic phase of these VO2 nanostructures ranged in size from 10 to 100 nm in cross-sectional diameter. At a current density of 2 A g-1, it demonstrated an excellent specific capacity of 615.8C g-1 when tested in a three electrodes setup with 1M Na2SO4 electrolyte [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e18\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eNiCo2O4 nanoflower thin films were successfully prepared by the chemical bath deposition process. The deposition temperature has a great influence on the shape of the resulting sample nanoflowers. The mature NiCo2O4 nanoflowers prepared at 363 K have a very high specific capacitance of 628 F/g at 5 mV/s [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. The large-scale syntheses of urchinlike NiCo2O4 nanostructures by a simple hydrothermal process yielded NiCo2O4 urchins that had outstanding specific capacitance of 1650 and 1348 F g-1 at current densities of 1 and 15 A g-1 [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. It is found that, the NiCo2O4 nanoflake array grown on Ni foam has a highly ordered\u003c/p\u003e \u003cp\u003estructure with a large specific surface area providing a large quantity of reactive sites and facilitating the transportation of electrons and electrolyte ions. This leads to an enhanced specific capacitance of 854.7 F g-1 at 1 A g-1 and even maintained at 745.1 F g-1 at 10 A g-1 for the NiCo2O4 nanoflake array [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e21\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eOne step hydrothermal synthesis is an efficient technique in the preparation of a wide range of materials and chemical compounds in one reaction process. It involves the mixing of selected precursors in water and then heating the mixture inside a sealed high-pressure reactor usually a Teflon-lined stainless-steel autoclave. Under high temperature and pressure water acts as a highly reactive medium that enables controlled nucleation, crystal growth and structural evolution. Because of its simplicity, versatility and capability to produce materials with tunable structures this method has been widely adopted in materials science, nanotechnology and chemistry. By controlling reaction parameters such as temperature, pressure, pH, precursor ratio and reaction duration it allows the tuning of morphology, particle size, crystallinity and overall physicochemical properties of the synthesised products. These advantages make the one-step hydrothermal method particularly valuable for developing advanced nanomaterials with application specific functionalities.\u003c/p\u003e \u003cp\u003eHydrothermal synthesis is particularly favoured for the preparation of nanomaterials, including metal oxides, sulfides and composite structures. In general hydrothermal treatment involves the preparation of aqueous precursor solutions which are then transferred to a Teflon container placed inside an autoclave the latter is then heated inside an oven. During heating different stages of the reactions may appear in sequence such as nucleation, cluster formation, aggregation and crystallization due to increased temperature and autogenous pressure. Organic additives, surfactants and structure-directing agents often influence the final particle shape, degree of agglomeration and surface features. Several hydrothermal routes have been published over the years for the synthesis of nickel cobaltite (NiCo₂O₄) nanopowders enabling the control of morphology and optimization of properties for different applications.\u003c/p\u003e \u003cp\u003eThe main goals of the present study are; to synthesize the nanostructured NiCo₂O₄ by hydrothermal technique and systematically investigate their morphological variations. It helps us to evaluate how the reaction parameters like reaction time, temperature, precursor ratio and pH influence the structural and morphological features NiCo₂O₄ samples regarding specific capacitance, rate capability and long-term cyclic stability. Though several researchers report on the synthesis of NiCo₂O₄ the exact information about the influence of each synthesis parameter on morphology is still limited. Because the electrochemical performance of NiCo₂O₄ is strongly dependent on morphology one has to investigate the\u003c/p\u003e \u003cp\u003eoptimised synthesis conditions. This investigation covers the existing gaps in offering indepth insights into the hydrothermal approach and its potential to produce improved materials for renewable energy storage and environmental applications. Further the results can be used to develop next-generation electrode materials possessing superior performance and stability.\u003c/p\u003e \u003cp\u003eAlthough much work has already illustrated the suitability of NiCo₂O₄ for high performance supercapacitors hydrothermal synthesis in particular offers better control over particle shape and size than more conventional solid state or high temperature combustion routes. Complementing the previous literature, the emphasis of the present work is thus on morphology optimization in NiCo₂O₄ structures through a soft chemical and solution-based approach. Reviewing the papers from 2001 up to the present it has been seen that a wide range of metal oxides of different morphologies have been synthesized by various chemical and physical methods. However better synthetic strategies must be developed continuously to tune morphology for their performance improvements.\u003c/p\u003e \u003cp\u003eBetween the years 2001 and 2005, the significant efforts were being directed toward the development of various metal oxide and polymer based electrode materials for energy storage applications. Various compositions, including PEO-KOH-H₂O polymer electrolytes, RuO₂\u0026middot;xH₂O/C composites, Mn₂O₃, SnO₂ xerogels, MnO₂, RuO₂ and RuO₂/CNT hybrids, were prepared through sol-gel processing, solution casting cathodic electrodeposition, electrochemical potential cycling and reduction-based chemical methods. Cyclic voltammetry, galvanostatic charge-discharge measurements and thermogravimetric analysis are some of the electrochemical studies conducted on these systems, showcasing attractive cycle efficiencies and capacitance values. Capacitive performances vary broadly generally between 90 to 720 F g-1 and up to 45 mF cm-2 and demonstrate early developments made in metal oxide based supercapacitor systems [\u003cspan additionalcitationids=\"CR24 CR25 CR26 CR27 CR28 CR29 CR30\" citationid=\"CR22\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e31\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eFrom 2006 to 2010, the field advanced further with the synthesis of materials such as polyaniline, metallic Ni, Co(OH)₂/CNT composites, RuO₂/CNT structures, single-walled carbon nanotubes (SWNTs), CrO₂, MnO₂/polypyrrole hybrids, graphite derivatives, Na₂Co₄- based compounds and RuCl₃\u0026middot;xH₂O. These materials were prepared through potentiodynamic deposition, general electrochemical deposition, cathodic methods, sol-gel synthesis, anodic techniques and precipitation routes. The resulting microstructures were highly varied, including spongy and porous textures, multi-walled tubular assemblies, spherical aggregates and mud cracked surface features. Electrochemical testing mainly cyclic voltammetry, galvanostatic charge discharge and thermal stability analysis demonstrated improvements in capacitive behavior, with reported values reaching as high as 785 F g-1. These findings confirmed the impact of controlled synthesis methodologies on enhancing electrochemical efficiency [\u003cspan additionalcitationids=\"CR33 CR34 CR35 CR36 CR37\" citationid=\"CR29\" class=\"CitationRef\"\u003e32\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e38\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eFrom 2011 to 2015, the investigations were increasingly focused on multicomponent and structurally engineered electrode materials. Typical synthesized compositions included Ni-Co alloys, NiCo₂, Ni₁/₃Co₁/₃Mn₁/₃(OH)₂, Ni-Co-Sn materials, NiCo₂O₄-rGO composites and NixCo₁-x(OH)₂. Representative synthesis methods in these works included the use of sol-gel routes, chemical reduction routes, Pechini methods, electrochemical approaches, precipitation, co-precipitation and template-free synthesis. The obtained morphologies were also highly varied, consisting of amorphous phases, nanowires, flower-like morphologies and highly porous structures. The corresponding electrochemical measurements continued to rely on cyclic voltammetry, galvanostatic charge discharge and thermogravimetric analysis. The life cycle of several materials was also extended to 5000 cycles. The capacitance values for this period have significantly increased, attaining a value as high as 2360 F g-1, reflecting major advances in morphological control and optimization of the material [\u003cspan additionalcitationids=\"CR31 CR32 CR33 CR34 CR35 CR36 CR37 CR38 CR39 CR40 CR41 CR42\" citationid=\"CR27\" class=\"CitationRef\"\u003e30\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e43\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eWithin the period from 2016 to 2024, research was extended rapidly upon the development of advanced nanostructured and composite materials for high-performance energy storage. Materials synthesized include NiCo₂O₄, Zn-Ni-Co oxides, biomass-derived carbons such as glucose-based carbon, NiCo₂, NiCo₂S compounds and multifunctional composites like CFAC/Ni-Co and Ni(OH)₂/N-Co the approaches used for their synthesis were also getting highly sophisticated and varied comprising the low-temperature chemical approach, coprecipitation, microwave assisted routes, hydrothermal processing and various wet chemical approaches. The morphologies obtained included well defined nanostructures, hierarchical flower-like shapes, hollow spheres and dandelion inspired architectures. The electrochemical performance increased remarkably, with some materials exhibiting capacitance values of up to 2525 F g-1, showing remarkable progress in electrode design and fabrication for next-generation supercapacitors. The collective developments hence show the uninterrupted evolution of material science toward higher efficiency, tunable morphology and enhanced energy storage capabilities [44\u0026ndash;53].\u003c/p\u003e"},{"header":"Experimental work","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eMaterials:\u003c/h2\u003e \u003cp\u003eNickel nitrate hexahydrate (Ni(NO3)2\u0026middot;6H2O), Cobalt nitrate hexahydrate (Co(NO3)2\u0026middot;6H2O), Urea as a precipitating agent, Distilled water, Propanol, Glycerine.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eSynthesis:\u003c/h3\u003e\n\u003cp\u003eNi/Co oxides were prepared by a facile hydrothermal synthesis method as described below. Firstly, a different molar ratio of nickel nitrate (Ni(NO3)2\u0026middot;6H2O) and cobalt nitrate (Co(NO3)2\u0026middot;6H2O) were dissolved in deionized (DI) water. Subsequently, certain amount of urea solution was slowly added dropwise into the above solution with vigorous stirring for 1 hour. After complete dissolution, the solution was transferred into a 100 ml Teflon lined autoclave and kept at 140\u0026deg;C for 6 hours. After reaction, the precipitate was collected and washed with deionised water and ethanol for several times. The obtained product was then dried in oven at 85\u0026deg;C for 12 hours and then calcined in air at 350\u0026deg;C step wise room temp to 350\u0026deg;C, 5\u0026deg;C for each minute and also next 2 hours to get the final sample. Then the product is obtained labelled as \u0026ldquo;NCO140\u0026rdquo;. For the comparison of different morphologies, the two other modified morphology material are synthesized by a using same precursors but different reaction condition i.e. varying the reaction conditions. The material synthesized at 160\u0026deg;C with the denoted as NCO160 while NCO180 is synthesized at 180\u0026deg;C. For a both material synthesis, the autoclave was kept for 6 hours at specified temperatures. The calcination and purification were carried out following the same process as similar for NCO140.\u003c/p\u003e"},{"header":"Result and Discussion","content":"\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003eMaterial Characterization\u003c/h2\u003e \u003cp\u003e \u003cb\u003eX-ray diffraction (XRD\u003c/b\u003e)\u003c/p\u003e \u003cp\u003eX-ray diffraction is a powerful analytical technique that is widely used to determine the crystallographic structure, phase composition, and structural integrity of material. In addition to confirming the crystal structure, XRD allows information on deviations from the ideal lattice due to internal stresses, strain and structural defects. Typically, such imperfections will manifest themselves as line broadening, shifting or change of intensity in the diffraction pattern, thereby allowing for evaluating microstructural characteristics. Due to its accuracy and reliability, XRD is a widely adopted technique in several fields, such as ceramics, metallurgy, pharmaceuticals, catalysis and energy storage. Therefore, it is also imperative for quality control because the presence of additional peaks in the diffractogram is indicative of secondary phases or impurities.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe X-ray diffraction analysis confirms the characteristic spinel-type crystal structure of NiCo₂O₄, thereby indicating that the nickel and cobalt ions occupy both tetrahedral and octahedral lattice sites in mixed valence states. The typical XRD pattern exhibits sharp diffraction peaks, which are indexed to the planes {111}, {220}, {311}, {400} and {511}, matching the standard spinel NiCo₂O₄ reference data. The sharp and intense peaks indicate good crystallinity and the formation of a single-phase structure free from impurity phases. Estimation of the size of crystallites through the analysis of peak broadening with the Scherrer equation provides information on microstrain and lattice distortions that may become significant from peak characteristics. The lattice parameters are calculated and they will be very useful in understanding structural stability, defect chemistry and potential electronic behavior. Also, confirmation of phase purity was made by comparing the obtained pattern with the standard JCPDS data, hence ensuring the successful synthesis of NiCo₂O₄ with an expected spinel configuration.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eFourier-transform infrared (FTIR)\u003c/h3\u003e\n\u003cp\u003eFourier-transform infrared spectroscopy of nickel cobaltite provides important information about the vibrational properties of the material, thus helping the researchers understand the bonding environment and functional groups associated with its spinel structure. A typical FTIR spectrum of NiCo₂O₄ shows distinct absorption bands mainly due to the metal-oxygen (M-O) vibrations involving Ni\u0026sup2;⁺ and Co\u0026sup3;⁺ ions. The most important peaks appear in the low-wavenumber region, normally within 400-600cm⁻\u0026sup1;, representing the stretching vibration of metal-oxygen bonds in the spinel lattice. These bands are\u003c/p\u003e \u003cp\u003erepresentative of the octahedral and tetrahedral coordination sites occupied by the metal ions. In some cases, extra broad features in the region of 1000-1300cm⁻\u0026sup1; may also appear, which can arise from complex metal-oxygen interactions or residual surface groups formed during synthesis. The positions, shapes and intensities of these peaks reflect the symmetry and structural integrity of the spinel framework. By comparing the obtained FTIR spectrum with the standard reference data, it allows for confirmation of the successful formation of a spinel phase of NiCo₂O₄ and allows the detection of surface modifications, structural distortions or impurities introduced during its synthesis. Thus, FTIR becomes a valuable complementary technique to verify structural and chemical characteristics of NiCo₂O₄.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eScanning Electron Microscopy (SEM):\u003c/h2\u003e \u003cp\u003e \u003c/p\u003e \u003cdiv id=\"Sec9\" class=\"Section3\"\u003e \u003ch2\u003e\u003c/h2\u003e \u003cp\u003eThe morphology of the NiCo₂O₄ prepared at 180\u0026deg;C was investigated by using Scanning Electron Microscopy (SEM) and the results are represented in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(a-c). The SEM images reveal that, the sample is composed of uniform spherical nanoparticles with an average particle size of about 11.9nm. At high magnification, the particles have a rough surface with porosity, indicating the presence of interconnected pores throughout the structure. This kind of porosity is beneficial for electrochemical applications in supercapacitors and electrocatalysis since it maximises the surface area and allows faster ion transportation during charge discharge processes. The SEM micrographs taken within the range of magnifications from 50,000X to the nanometre scale up to the 1000 nm view clearly show the hierarchical features of this material. In addition to the spherical nanoparticles, the NiCo₂O₄ sample also exhibited nanoflower-like morphologies where the structures seem to self-assemble in flower-shaped clusters with diameters varying from ca. 5 \u0026micro;m up to 50 \u0026micro;m. This kind of combination of nanoscale spheres and microscale flower-like architecture implies an effective growth mechanism favourable to improve electrochemical performance by giving rise to a high degree of surface accessibility and structural stability.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e\n\u003ch3\u003eEnergy Dispersive X-ray (EDAX)\u003c/h3\u003e\n\u003cp\u003e \u003c/p\u003e \u003cp\u003eThe EDAX analysis of the synthesised NiCo₂O₄ was performed to determine its elemental composition and confirm the stoichiometric ratio of the mixed metal oxide. The atomic ratio between nickel and cobalt has been confirmed to be approximately 1:2 with the appearance of well-defined characteristic X-ray peaks such as the Ni Kα peak at about 7.78 keV and the Co Kα peak at about 7.01 keV. Oxygen is part of the basic oxide lattice component, direct EDAX detection has a limitation due to the low atomic number. Hence the presence of oxygen can be inferred from the structural composition and the overall stoichiometric balance. No additional peak obviously signifies the absence of impurities or unwanted elemental contamination in the sample. This suggests successful synthesis with\u003c/p\u003e \u003cp\u003ehigh purity. Further confirmation of elemental mapping also proved that Ni and Co were distributed quite homogeneously across the entire sample, reflecting good homogeneity in the material. These are particularly important in order for the material to be used in supercapacitors, electrocatalysis and other energy storage devices where performance strongly relies on the correct elemental ratio and appropriate distribution of its active components.\u003c/p\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eX-ray Photoelectron Spectroscopy (XPS)\u003c/h2\u003e \u003cp\u003eThe XPS analysis further confirms the successful formation of pure spinel NiCo₂O₄ without any impurities detectable by this technique. Only nickel, cobalt and oxygen elements could be identified from the survey spectrum, which confirms that high chemical purity is realised from this 180\u0026deg;C synthesised sample.\u003c/p\u003e \u003cp\u003eThe two major spin-orbit peaks in the Ni 2p spectrum occur at binding energies of ~\u0026thinsp;855.6 eV (Ni 2p₃/₂) and ~\u0026thinsp;873.2 eV (Ni 2p₁/₂) respectively with well-defined satellite peaks. These features indicate the coexistence of mixed oxidation states Ni\u0026sup2;⁺ and Ni\u0026sup3;⁺, a characteristic feature of inverse spinel structures that enhances electronic conductivity and therefore promotes fast redox reactions.\u003c/p\u003e \u003cp\u003eSimilarly, the Co 2p spectrum displays strong peaks at about 780.4 eV (Co 2p₃/₂) and 795.6 eV (Co 2p₁/₂), which confirm the existence of both Co\u0026sup2;⁺ and Co\u0026sup3;⁺ cations within the host lattice. The shake-up satellite peaks associated with these further supports the mixed valency nature of cobalt, which plays a crucial role in enhancing charge-transfer kinetics in electrochemical systems.\u003c/p\u003e \u003cp\u003eThe major peak at approximately 529.3 eV in the O 1s spectrum is assigned to lattice oxygen (O\u003csup\u003e2\u0026minus;\u003c/sup\u003e). The additional peaks at higher binding energy in the region of 531.0-532.0 eV are ascribed to surface hydroxyl groups and adsorbed oxygen species. Such surface oxygen states enhance the electrochemical activity due to the promotion of surface redox behavior and the improvement of wettability.\u003c/p\u003e \u003cp\u003eThe presence of mixed oxidation states of Ni and Co atoms, demonstrates strong electronic interactions within the spinel. Enhanced redox activity and enhanced electronic conductivity make NiCo₂O₄ synthesized at 180\u0026deg;C an extremely promising material for supercapacitors, batteries, electrocatalysis and other energy-storage applications.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003eBrunauer Emmett Teller (BET)\u003c/h2\u003e \u003cp\u003eThe mesoporous characteristic of NiCo₂O₄ prepared at 180\u0026deg;C was further verified by BET surface area analysis, showing a representative Type IV nitrogen adsorption-desorption isotherm with a well defined H₃ type hysteresis loop. The results reveal relatively high specific surface areas, indicating plenty of active sites and interconnected pore channels that would facilitate charge storage and ion transport in electrochemical applications. Moreover, Barrett Joyner Halenda (BJH) pore size distribution analysis shows the material has an average diameter of ca. 10\u0026ndash;15 nm, and the majority of pores fall into the mesoporous range of 2\u0026ndash;50 nm. Such a mesoporous architecture facilitates the diffusion of electrolyte ions in the whole electrode material, increases ion accessibility to active sites and thus leads to excellent electrochemical performances in supercapacitors and batteries.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe isotherm features a hysteresis loop in the desorption branch at higher relative pressures, indicating capillary condensation in mesopores, while the adsorption branch reveals a gradual increase in the volume of adsorbed nitrogen at low relative pressures, corresponding to the monolayer-multilayer adsorption of nitrogen on pore walls. With its large surface area and porous texture that enhance electrochemical performance by facilitating redox reactions at the electrode-electrolyte interface and enabling efficient ion transport, NiCo₂O₄ is a promising material for supercapacitor and catalytic applications\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003eElectrochemical study\u003c/h2\u003e \u003cp\u003eIn order to test the capacitive behaviour CV, galvanostatic charge-discharge and EIS will be used. Cyclic voltammetry is probably the single most popular experimental technique used by the electrochemist. Despite this popularity, many users receive little formal training in this technique. Galvanostatic Charge Discharge (GCD) tests or Constant Current Charging/Discharging are often employed to evaluate energy storage systems and materials, including those involved in electrochemical capacitors. So, an electroanalytical experiment used to study the electrochemical properties of an electroactive species in solution or adsorbed on an electrode surface. Electrochemical impedance spectroscopy provides kinetic and mechanistic data on a wide variety of electrochemical systems and hence finds broad use in such areas as corrosion studies, semiconductor science, energy conversion and storage technology, chemical sensing and biosensing, noninvasively diagnostics, so an electroanalytical experiment used to study the electrochemical properties of an electroactive species in solution or adsorbed on an electrode surface.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003eCyclic voltammetry(CV)\u003c/h2\u003e \u003cp\u003eThe capacitive performance of NiCo₂O₄ was further investigated by CV in the potential window between 0 and 0.5V. In the following, the effect of the scan rate on the redox response was systematically studied by varying the scan rate from 5 to 100 mV/s. With increasing scan rate, both the anodic and cathodic peak currents increased proportionally, representing a typical diffusion-controlled process and good electrochemical reversibility. Current responses approximately range from 0.2 A to 0.4 A with slight broadening of the peaks at higher scan rates that can be ascribed to polarization and ohmic effects in the electrode material\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe capacitance values were integrated from the areas under the CV curves and showed the expected trend, varying with scan rate 512 F/g at 5 mV/s, 410 F/g at 20 mV/s, 328 F/g at 50 mV/s, 280 F/g at 80 mV/s and 250 F/g at 100 mV/s. Such a decrease in capacitance with scan rate increase is normal for pseudocapacitive materials, since higher scan rates reduce the time for which electrolyte ions can diffuse deeper into the porous structure. These results thus indicate very good capacitive behaviour of NiCo₂O₄ and its potential as an electrode material in supercapacitors.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003eGalvanostatic charge-discharge (GCD)\u003c/h2\u003e \u003cp\u003eGalvanostatic charge-discharge measurements of NiCo₂O₄ were conducted in a potential window between 0.0 and 0.5 V with time recorded from 2 to 18 seconds. The GCD curves obtained display almost symmetrical charge and discharge profiles, revealing\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eexcellent reversibility with stable electrochemical behaviour. Charge-discharge segments demonstrate mostly linear and triangular profiles, which are very typical for pseudocapacitive materials. A slight deviation from perfect linearity is seen accordingly, it could be understood that Faradaic redox reactions make a significant contribution to the charge storage mechanism as a whole. Charging starts from about 0.0 V and proceeds to 0.5 V, while it discharges symmetrically back to the initial potential, proving good coulombic efficiency. The total time for charge and discharge is roughly 20 seconds indicating moderate current density and good energy storage behaviour. These observations prove that NiCo₂O₄ possesses both high reversibility and stable electrochemical performance, making it one of the most promising electrode materials for supercapacitor applications.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003eElectrochemical Impedance Spectroscopy (EIS)\u003c/h2\u003e \u003cp\u003eEIS was used to investigate the charge-transfer resistance and ion diffusion behaviour of NiCo₂O₄, so as to gain insight into its suitability as an efficient electrode material. The Nyquist plot of this material generally shows a semicircular arc in the high-frequency region\u003c/p\u003e \u003cp\u003edue to the charge-transfer resistance, R ct at the interface between the electrode and electrolyte. In the low-frequency region, there is a nearly linear segment, which is characteristic of Warburg impedance reflecting ion diffusion in the electrode. The fairly small R ct value indicates an enhancement in electrical conductivity. It also shows the, fast chargetransfer kinetics, which are necessary for high-performance electrochemical applications. Furthermore, the slope of the Warburg region indicates efficient ion transport through the mesoporous electrode structure. A combination of these features-low charge-transfer resistance and effective ion diffusion-also permits NiCo₂O₄ to have appropriate synergistic electronic and ionic transport properties, desirable for superior performance in supercapacitors and battery electrodes among other energy storage devices.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"Conclusion","content":"\u003cp\u003eThe present study depicted NiCo₂O₄ as a highly promising electrode material for supercapacitor applications owing to its excellent structural and electrochemical properties. Structural characterization using XRD confirmed the formation of a pure spinel phase, while FTIR analysis validated the presence of characteristic metal-oxygen vibrations within the lattice. The SEM investigations further revealed the uniform spherical nanoparticles and nanoflower-like architectures with a porous and rough surface, which provides a high surface area and interconnected channels. EDAX analysis confirmed the stoichiometric composition and homogeneous distribution of Ni and Co. XPS verified the coexistence of mixed oxidation states such as Ni\u0026sup2;⁺/Ni\u0026sup3;⁺ and Co\u0026sup2;⁺/Co\u0026sup3;⁺ and the presence of lattice oxygen and surface hydroxyl groups. BET studies further revealed a mesoporous structure with pore diameters in the 10\u0026ndash;15 nm range, which facilitates rapid ion diffusion and enhances electrolyte accessibility.\u003c/p\u003e \u003cp\u003eElectrochemical characterisation showed that NiCo₂O₄ exhibited excellent performance as a pseudocapacitive material. Cyclic voltammetry exhibited high values of\u003c/p\u003e \u003cp\u003especific capacitance, amounting to 512 F/g at 5 mV/s, decreasing moderately at higher scan rates, which is indicative of diffusion-limited ion transport at elevated rates. The GCD curves showed almost symmetrical triangular shapes, indicating high reversibility with good coulombic efficiency and stable energy storage behaviour. EIS further showed low chargetransfer resistance and efficient ion diffusion within the electrode, supporting rapid redox kinetics and superior electronic and ionic transport properties.\u003c/p\u003e \u003cp\u003eTailored morphology, high surface area, mixed oxidation states and mesoporous architecture allow NiCo₂O₄ to achieve superior electrochemical performance, making it a promising candidate for high-performance supercapacitors. The synthesis route should be further optimized by methods such as hydrothermal, sol-gel and co-precipitation, along with designing advanced NiCo₂O₄ based composites in order to further enhance electrical conductivity, surface area and stability during long term operation. This development will unlock the full potential of NiCo₂O₄ for next generation energy storage applications, while enabling efficient, cost-effective and sustainable supercapacitor technology.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eall other other guided me for this work\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eI would like to express my sincere gratitude to all the institutions and individuals who supported me throughout the completion of my work. I am deeply thankful to DKASC College, Ichalkaranji, YC College, Satara, DY Patil University, Kolhapur, Shivaji University, Kolhapur, and Mumbai University, Mumbai for their valuable guidance, facilities, and encouragement. Their support has played a significant role in the successful completion of this work\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eYan SX, Luo SH, Sun MZ, Wang Q, Zhang YH, Liu X. Facile hydrothermal synthesis of urchin-like NiCo2O4 as advanced electrochemical pseudocapacitor materials. Int J Energy Res. 2021;45(14):20186\u0026ndash;98. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1002/er.7101\u003c/span\u003e\u003cspan address=\"10.1002/er.7101\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKarthikeyan S, Narenthiran B, Sivanantham A, Bhatlu LD, Maridurai T, Supercapacitor. Evolution and review. 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ACS Sustainable Chemistry \u0026amp; Enginee\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":false,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Symmetric super capacitor, Nanomaterial","lastPublishedDoi":"10.21203/rs.3.rs-8333957/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8333957/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eIn this paper, we searching the temperature dependant and temperature changing effect of the morphology of material, porosity and electrochemical performance of NiCo₂O₄ nanostructures synthesized material at 140\u0026deg;C, 160\u0026deg;C and 180\u0026deg;C for supercapacitor applications. With a temperature step wise rise, the obtained materials have clear morphological transformation starting from spherical nanoparticles to structures transferring to flower-like morphologies which are a type of grass over the sphere. These structural changes have definitely affected the material porosity and surface area, two major factors to enhance energy storage of supercapacitor performance. Electrochemical experiments such as electrochemical impedance, galvanostatic charge discharge and cyclic voltammetry reveal the optimum temperature for outstanding performance with regard to specific capacitance and cycle stability. The results show that the synthesis temperature regulation is a valid strategy for tuning the characteristics of NiCo₂O₄ toward high-performance energy storage.\u003c/p\u003e","manuscriptTitle":"Temperature Dependent Synthesis of NiCo₂O₄ Nanostructures and Their Supercapacitor Performance: Morphological Transitions from Spherical to Flower-Like Structures","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-12-15 06:53:19","doi":"10.21203/rs.3.rs-8333957/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"ba2e47d4-7953-4e4e-a788-f771780e01eb","owner":[],"postedDate":"December 15th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2026-02-05T04:40:02+00:00","versionOfRecord":[],"versionCreatedAt":"2025-12-15 06:53:19","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8333957","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8333957","identity":"rs-8333957","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}