Sol-gel synthesis,characterization, and supercapacitor applications of MCo2O4 (M = Ni,Mn, Cu,Zn) cobaltite spinels

High performance MCo₂O₄spinels (M = Ni, Mn, Cu, Zn) were synthesized by the sol gel method (citrate) and their capacitive behavior was investigated in alkaline electrolyte. Their structural, morphological, functional groups and textural properties were characterized by TG/DSC, XRD, SEM, FTIR, EDS and BET. The capacitive properties of spinel MCo₂O₄ samples were thoroughly investigated in 1?M KOH aqueous electrolyte using cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The results revealed high stability of the samples and excellent electrochemical reversibility, and exhibited specific capacity depending on the nature of the transition metal ion M. A high specific capacitance of 285?F?g^?1 was measured for CuCo₂O₄ and a low capacitance of 158?F?g^?1 for ZnCo₂O₄.In addition, MCo₂O₄ spinels displayed good stability during long-term cycles with a cycling efficiency which exceeds75% after 1000 cycles. The obtained results classified MCo₂O₄ cobaltite spinels as most promising materials for their application in super capacitors.     

Hierarchical Co3O4@ZnWO4 core/shell nanostructures on nickel foam: Synthesis and electrochemical performance for supercapacitors

To improve the electrochemical properties of Co₃O₄ for supercapacitors application, a hierarchical Co₃O₄@ZnWO₄ core/shell nanowire arrays (NWAs) material is designed and synthesized successfully via a facile two-step hydrothermal method followed by the heat treatment. Co₃O₄@ZnWO₄ NWAs exhibits excellent electrochemical performances with areal capacitance of 4.1 F cm⁻² (1020.1 F g⁻¹) at a current density of 2 mA cm⁻² and extremely good cycling stability (99.7% of the initial capacitance remained even after 3000 cycles). Compared with pure Co₃O₄ electrodes, the results prove that this unique hierarchical hybrid nanostructure and reasonable assembling of two electrochemical pseudocapacitor materials are more advantageous to enhance the electrochemical performance. Considering these remarkable capacitive behaviors, the hierarchical Co₃O₄@ZnWO₄ core/shell NWAs nanostructure electrode can be revealed promising for high-performance supercapacitors.     

Hydrazine hydrate-induced hydrothermal synthesis of MnFe2O4 nanoparticles dispersed on graphene as high-performance anode material for lithium ion batteries

Herein, a MnFe₂O₄/graphene (MnFe₂O₄/G) nanocomposite has been synthesized via a facile N₂H₄·H₂O-induced hydrothermal method. During the synthesis, N₂H₄·H₂O is employed to not only reduce graphene oxide to graphene, but also prevent the oxidation of Mn²⁺ in alkaline aqueous solution, thus ensuring the formation of MnFe₂O₄/G. Moreover, MnFe₂O₄ nanoparticles (5–20 nm) are uniformly anchored on graphene. MnFe₂O₄/G electrode delivers a large reversible capacity of 768 mA h g⁻¹ at 1 A g⁻¹ after 200 cycles and high rate capability of 517 mA h g⁻¹ at 5 A g⁻¹. MnFe₂O₄/G holds great promise as anode material in practical applications due to the outstanding electrochemical performance combined with the facile synthesis strategy.     

Magnetic properties and self-heat behaviors of core@shell structured MnFe2O4@Fe3O4 magnetic nanoparticles

In this work, a facile solvothermal synthesis of MnFe₂O₄ nanoparticles is followed by an easy and reproducible process to envelop the synthesized MnFe₂O₄ nanoparticles with iron oxide nanoparticles using ethanol and ethylene glycol as solvents. All prepared MnFe₂O₄ nanoparticles show a homogenous distribution of spherical particles with an average particle size between 12 and 16 nm. The encapsulation process of MnFe₂O₄ nanoparticles does not affect their homogenous distribution with a very thin layer of Fe₃O₄ on the shell structure. The magnetic properties showed a superparamagnetic character with enhanced magnetic properties of MnFe₂O₄@Fe₃O₄ compared to pure MnFe₂O₄, which has been verified by magnetization and electron spin resonance. The heating efficiency of the prepared samples was evaluated in terms of the specific loss power using the calorimetric method. The synthesized MnFe₂O₄ nanoparticles show a significantly high value of about 72 W/g, which got doubled in the core@shell structure and reached 140 W/g at 189 kHz and 10kA/m of the magnetic field.     

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

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

The influence of reactive milling on the structure and magnetic properties of nanocrystalline MnFe2O4

Nanocrystalline manganese ferrites (MnFe₂O₄) have been synthesized by direct milling of metallic manganese (Mn) and iron (Fe) powders in distilled water (H₂O). In order to overcome the limitation of wet milling, dry milling procedure has also been utilized to reduce crystallite size. The effects of milling time on the formation and crystallite size of wet milled MnFe₂O₄ nanoparticles have been investigated. It has been observed that single phase 18.4 nm nanocrystalline MnFe₂O₄ is obtained after 24 h milling at 400 rpm. Further milling caused deformation of the structure as well as increased crystallite size. With the aim of reducing the crystallite size of 18.4 nm, MnFe₂O₄ sample dry milling has been implemented for 2 and 4 h at 300 rpm. As a result, the crystallite size has been reduced to 12.4 and 8.7 nm, respectively. Effects of the crystalline sizes on magnetic properties were also investigated. Magnetization results clearly demonstrated that crystallite size has much more effect on the magnetic properties than average particle size.     

Characterization and property of magnetic ferrite ceramics with interesting multilayer structure prepared by solid-state reaction

Polyhedral MnFe₂O₄ with multilayer structure was successfully synthesized, and the possible originating mechanism of multilayer structure was firstly determined in current study. The phase formation, morphology evolution and interface reaction of the solid-state reaction of MnO₂ and Fe₂O₃ mixture under air and reduction atmospheres were comparatively investigated, and the microwave absorption property of polyhedral MnFe₂O₄ with multilayer structure were discussed via the XRD, SEM, XPS, TEM, AFM and vector network analyzer measurements. Experiment results showed that multilayer MnFe₂O₄ can be synthesized both in the air at 1200–1300 °C and in 4 vol%CO at 1000–1100 °C. The reduction atmosphere was favorable to the formation of multilayer structure of MnFe₂O₄ due to the occurrence of multilayer MnO as the intermedium. In addition, morphology evolution demonstrated that the particle size of MnO₂ after reduction was decreased remarkably which was also beneficial to the formation of MnFe₂O₄. However, air atmosphere is unfavorable to the generation of MnFe₂O₄ due to the recrystallization growth of Fe₂O₃ to lump impeding the element diffusion. Resultantly, the required temperature for the synthesis of MnFe₂O₄ in air was much higher than that in 4 vol% CO. One possible mechanism for the polyhedral MnFe₂O₄ with multilayer structure was based on the combination of the greater growth speed of (111) plane in the cubic MnFe₂O₄ crystal and terrace-ledge-kink (TLK) growth model. Moreover, multilayer MnFe₂O₄ prepared by the solid-state reaction presented good microwave absorbing property compared with that of the ferrites synthesized via the representative wet chemistry and combined methods.     

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.     

Solid-state combustion synthesis of spinel LiMn2O4 using glucose as a fuel

Spinel LiMn₂O₄ cathode material was rapidly synthesized in 1 h by solid-state combustion synthesis using metal carbonates as metal ion sources and glucose as a fuel. The effect of different amounts of glucose on the structure and electrochemical performance of as-prepared LiMn₂O₄ was investigated by X-ray diffraction (XRD), scanning electron micrographs (SEM), galvanostatic charge–discharge test, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). LiMn₂O₄ spinel was identified as the main crystalline phase with the presence of minor Mn₃O₄. The amount of glucose greatly affected the formation of Mn₃O₄. The optimal content of glucose was found to be 10 wt%. Under this condition, the Mn₃O₄ peaks almost disappeared, and high-purity spinel LiMn₂O₄ was obtained. Its initial discharge specific capacity of was 125.9 mAh/g, and discharge specific capacity retained at 105.2 mAh/g after 40 cycles. The detail influence of glucose on the electrochemical activity, reversibility and cycling performance of LiMn₂O₄ was discussed.     

Novel photocatalytic performance of magnetically recoverable MnFe2O4/BiVO4 for polluted antibiotics degradation

In the study, we successfully decorated MnFe₂O₄ on BiVO₄ to highly improve its photocatalytic activity for degradation of tetracycline as well as its magnetically recovery. The decoration of MnFe₂O₄ on BiVO₄ led to formation of MnFe₂O₄/BiVO₄ Z scheme heterojunction to effectively prevent the charge recombination in each material. Upon visible light, the MnFe₂O₄/BiVO₄ heterojunction produced significant available amounts of e^? and h⁺ existing in the conduction band of the MnFe₂O₄ and the valence band of the BiVO₄, respectively. These produced e^? on the conduction band of the MnFe₂O₄, which reduction potential was approximately ?0.41 eV, exhibited strong reduction potential reducing oxygen to produce ^?O_2^? radicals while h⁺ on the valence band of the BiVO₄, which oxidation potential was 2.77 eV, showed strong oxidation potential oxidizing water and hydroxyl groups to produce ^?OH radicals. These generated active oxygen radicals effectively degraded TC in water (~92%). The used photocatalysts were easily recovered from photocatalytic suspension using an external magnet due to high magnetically activity of the MnFe₂O₄, which tightly bonded with BiVO₄ in the MnFe₂O₄/BiVO₄ heterojunction. Finally, the recovered MnFe₂O₄/BiVO₄ heterojunction was very active and stable for tetracycline degradation in long-term process.     

Co3O4 thin film prepared by a chemical bath deposition for electrochemical capacitors

Co₃O₄ thin film is synthesized on ITO by a chemical bath deposition. The prepared Co₃O₄ thin film is characterized by X-ray diffraction, and scanning electron microscopy. Electrochemical capacitive behavior of synthesized Co₃O₄ thin film is investigated by cyclic voltammetry, constant current charge/discharge and electrochemical impedance spectroscopy. Scanning electron microscopy images show that Co₃O₄ thin film is composed of spherical-like coarse particles, together with some pores among particles. Electrochemical studies reveal that capacitive characteristic of Co₃O₄ thin film mainly results from pseudocapacitance. Co₃O₄ thin film exhibits a maximum specific capacitance of 227 F g⁻¹ at the specific current of 0.2 A g⁻¹. The specific capacitance reduces to 152 F g⁻¹ when the specific current increases to 1.4 A g⁻¹. The specific capacitance retention ratio is 67% at the specific current range from 0.2 to 1.4 A g⁻¹.     

Facile synthesis,antibacterial mechanisms and cytocompatibility of Ag–MnFe2O4 magnetic nanoparticles

Magnetic MnFe₂O₄ nanoparticles containing 0, 1 and 3 at.% silver, respectively were synthesized by one-pot sol-gel method for antibacterial applications in biomedical fields. Material characterizations indicate that MnFe₂O₄ begins crystallization at 134 °C and oxidation at 450 °C, the grain size and agglomeration degree increase with the silver content and silver exists as metallic state for the particles. The saturation magnetization decreases with the sintering temperature and slightly increases with the silver content, with the maximum of 50.0 emu/g obtained. Antibacterial tests by plate counting and PI-Hoechst 33342 staining suggest that the antibacterial activity of Ag–MnFe₂O₄ nanoparticles is silver content-dependent. Silver ions concentration measurement, β-galactosidase activity assay and transmission electron microscopic observation show that the antibacterial activity is dominated by the actions of the released silver ions, rather than the membrane cell impairment or reactive oxygen species-induced oxidative stress mechanism. MC3T3-E1 cell test demonstrates the best cytocompatibility of the nanoparticles with 3 at.% silver, which is likely related to the reduced cell endocytosis of the aggregated particles. The combination of magnetism, antibacterial activity and biocompatibility would make Ag–MnFe₂O₄ nanoparticles a potential multi-functional material in various biomedical applications.     

Copper substituted nickel ferrite nanoparticles anchored onto the graphene sheets as electrode materials for supercapacitors fabrication

Nickel ferrites with high theoretical capacitance value as compared to the other metal oxides have been applied as electrode material for energy storage devices i.e. batteries and supercapacitors. High tendency towards aggregation and less specific surface area make the metal oxides poor candidate for electrochemical applications. Therefore, the improvements in the electrochemical properties of nickel ferrites (NiFe₂O₄) are required. Here, we report the synthesis of graphene nano-sheets decorated with spherical copper substituted nickel ferrite nanoparticles for supercapacitors electrode fabrication. The copper substituted and unsubstituted NiFe₂O₄ nanoparticles were prepared via wet chemical co-precipitation route. Reduced graphene oxide (rGO) was prepared via well-known Hummer's method. After structural characterization of both ferrite (Ni_1-xCu_xFe₂O₄) nanoparticles and rGO, the ferrite particles were decorated onto the graphene sheets to obtain Ni_1-xCu_xFe₂O₄@rGO nanocomposites. The confirmation of preparation of these nanocomposites was confirmed by scanning electron microscopy (SEM). The electrochemical measurements of nanoparticles and their nanocomposites (Ni_0.9Cu_0.1Fe₂O₄@rGO) confirmed that the nanocomposites due to highly conductive nature and relatively high surface area showed better capacitive behavior as compared to bare nanoparticles. This enhanced electrochemical energy storage properties of nanocomposites were attributed to the graphene and also supported by electrical (I-V) measurements. The cyclic stability experiments results showed ~65% capacitance retention after 1000 cycles. However this retention was enhanced from 65% to 75% for the copper substituted nanoparticles (Ni_0.9Cu_0.1Fe₂O₄) and 65–85% for graphene based composites. All this data suggest that these nanoparticles and their composites can be utilized for supercapacitors electrodes fabrication.     

Electrochemical performance of NiFe2O4 nanostructures incorporating activated carbon as an efficient electrode material

The quest for cost-efficient electro-active materials exhibiting high specific capacitance is currently a key focus in energy-related research. Owing to their high capacitance values, metal oxides (MOs) are preferably being utilized for energy storage applications as electrode materials in supercapacitors. However, the electrochemical performance of MOs is hindered due to less specific surface area and high tendency towards aggregation. Therefore, tuning in electrochemical activity of MOs is essential. In this framework, NiFe₂O₄ was prepared using a facile and cost-effective citrate-gel followed by auto-ignition method, and was incorporated with activated carbon contents to tune the electrochemical performance. Formation of inverse spinel structure of NFO and its stability throughout the compositions was examined using X-ray diffraction analysis. Well-dispersed, spherical and porous morphological features were visualized using a field emission scanning electron microscope. The electrochemical analysis was conducted using CH instruments 660 E via freshly prepared 4 M KOH solution. Cyclic voltammetry was carried out at constant potential window of 0.25–0.65 V and different scan rates (0.009–0.08 Vs^-1). The pseudo-capacitive behavior was perceived from occurrences of oxidation/reduction peaks. In addition, charge/discharge curves revealed cyclic stability over long range cycles. Specific capacitance, discharge time, energy and power density values were also measured for all the compositions and NFO with 1% activated carbon was found to be the most suitable candidate for use as electrode materials in the present work.     

High-performance supercapacitor based on V2O5/carbon nanotubes-super activated carbon ternary composite

A ternary composite of V₂O₅/carbon nanotubes/super activated carbon (V₂O₅/CNTs–SAC) was prepared by a simple hydrothermal method and used as a supercapacitor electrode material. The electrochemical performance of the electrode was analyzed using cyclic voltammetry, galvanostatic charge/discharge measurements, and electrochemical impedance spectroscopy, which were performed in 2 M NaNO₃ as the electrolyte. The V₂O₅/CNTs–SAC nanocomposite exhibited a specific capacitance as high as 357.5 F g⁻¹ at a current density of 10 A g⁻¹, which is much higher than that of either bare V₂O₅ nanosheets or a V₂O₅/CNTs composite. Furthermore, the capacitance increased to 128.7% of the initial value after 200 cycles, with 99.5% of the maximum value being retained after 1000 cycles. These results demonstrated that the V₂O₅/CNTs–SAC ternary composite is suitable for use as an electrode material for supercapacitors.     

Influence of calcination rate on morphologies and magnetic properties of MnFe2O4 nanofibers

In the present study, we succesfully synthesized electrospun MnFe₂O₄ nanofibers (NFs) from poly(N-vinylpyrrolidone)/manganese(II) nitrate composite by electrospinning and then as-spun NFs were calcined 450 °C for 2 h in air atmosphere to remove the polymer matrix and fabricate inorganic MnFe₂O₄ nanofibers. In order to investigate the sintering behavior of MnFe₂O₄ nanofibers in air atmosphere, the synthesized as-spun nanofibers were calcined with different calcination rates. Thus the effect of calcination rate on structure and morphology of nanofibers were discussed clearly. The structural, magnetic, morphological, spectroscopic and thermal characterizations were also done by XRD, VSM, TEM, SEM, FTIR and TG analysis. In the presence of slow calcination rate, only peaks of MnFe₂O₄ could be observed on other hand in the presence of rapid calcination rate, formation of an impurity was observed. Scanning electron microscope images revealed that MnFe₂O₄ nanorods possess a broader range size distribution with higher particle size. Also, magnetic properties were both size and shape dependent.     

Effect of ZnBi2O4 and Bi2O3 addition on the densification,microstructure, and varistor properties of ZnO varistors

In this study, 1 wt% Bi₂O₃ (1B), 1 wt% ZnBi₂O₄ (1BZ), and a composite (a mixture of 1 wt% Bi₂O₃ and various amounts (1-4 wt%) of ZnBi₂O₄ ,1B1BZ-1B4BZ) were added to ZnO varistors to investigate the effects of additives on the densification, microstructure, and varistor performance. The results showed that the addition of ZnBi₂O₄ can lower the densification temperature to about 850^oC. When the additive was changed from 1 wt% Bi₂O₃ to 1 wt% ZnBi₂O₄, the α value increased from 42 to 54, the breakdown voltage increased from 775 V/mm to 1011 V/mm, and the leakage current decreased to 0.11 μA. Additions of ZnBi₂O₄ and transition metal cations as donor dopants for the ZnO varistors promote oxygen chemisorption at grain boundaries, resulting in greater α value and lower leakage currents. This suggests the addition of ZnBi₂O₄ can effectively promote densification and improve the varistor properties of ZnO varistors.     

Hydrothermally synthesized microrods and microballs of NiCo2O4 for supercapacitor application

The microrods and microballs of NiCo₂O₄ are successfully synthesized by the hydrothermal method. The effect of ammonium hydroxide and ammonium fluoride on the surface microstructure is observed. The prepared microrods and microballs of NiCo₂O₄ are analyzed by various analytical tools like powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), with energy dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS). The electrochemical properties are studied by using cyclic voltammetry (CV), galvanostatic charge discharge (GCD), and electrochemical impedance spectroscopy (EIS), using the workstation Biologic SP-200. The maximum specific capacitance of the NiCo₂O₄ microrods electrode is 1671 F/g. The areal specific capacitance of the NiCo₂O₄ microrods electrode is 284 mF/g. The energy density and power density of microrods of NiCo₂O₄ electrode are 19 Wh/Kg and 282 W/kg, respectively. The equivalent series resistance (Rs) is 0.62 Ω for NiCo₂O₄ microrods.     

Composite electrodes for electrochemical supercapacitors

Manganese dioxide and Ag-doped manganese dioxide powders were prepared by a chemical precipitation method using KBH₄ as a reducing agent. The powders were studied by X-ray analysis, thermogravimetry, and electron microscopy. Composite electrodes for electrochemical supercapacitors (ES) were fabricated by impregnation of slurries of the precipitated powders and carbon black into porous nickel foam current collectors. In the composite electrodes, carbon black nanoparticles formed a secondary conductivity network within the nickel foam cells. Obtained composite electrodes, containing manganese dioxide and 20 wt% carbon black with total mass loading of 50 mg cm⁻², showed a capacitive behavior in the 0.5 M Na₂SO₄ solutions. The capacitive behavior of the composite electrodes can be improved by mixing of manganese dioxide and carbon black in solutions or using Ag-doped manganese dioxide powders. The highest specific capacitance (SC) of 150 F g⁻¹ was obtained at a scan rate of 2 mV s⁻¹. The electrodes showed good cycling behavior with no loss in SC during 1,000 cycles.     

NiFe2O4/SiO2 nanostructures as a potential electrode material for high rated supercapacitors

Engineered materials are crucial for the higher efficiency of supercapacitors. Current work presents roughly shaped spherical NiFe₂O₄ nanoparticles dispersed in the SiO₂ matrix NiFe₂O₄/SiO₂ as a newfangled electrode material for supercapacitors with remarkable performance. Designing the NiFe₂O₄/SiO₂ nanostructure with a sol-gel method followed by the Stober method to grow silica has instigated NiFe₂O₄/SiO₂ as dynamic material with higher electrochemical activity. Physicochemical aspects of NiFe₂O₄/SiO₂ nanostructures are evaluated using Fourier-transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy analysis. The electrochemical activity is evaluated by cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) representing the comparable efficiency and reversibility of the electrode materials. The prepared electrode shows a capacitance of 925 F/g (154.1 mAh/g or 555 C/g) at 1 A/g, with 95.5% capacitance retention after 5000 cycles at 20 mA/cm². The improved electrochemical performance of the NiFe₂O₄/SiO₂ electrode can be subjected to prompt diffusion process provided by NiFe₂O₄/SiO₂ and enhanced redox reactions owing to the high surface area. The mentioned features decrease the total impedance of the electrodes as suggested by electrochemical impedance spectroscopy (EIS).