Temperature-Driven Surface Modifications of Hydrothermally Synthesized ZnFe₂O₄ for High-Efficiency Supercapacitors

Temperature-Driven Surface Modifications of Hydrothermally Synthesized ZnFe₂O₄ for High-Efficiency Supercapacitors | 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-Driven Surface Modifications of Hydrothermally Synthesized ZnFe₂O₄ for High-Efficiency Supercapacitors Nidhi Tiwari, Priya Gaikwad, R. K. Kamat, Shrinivas Kulkarni This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7019735/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 demonstrate the synthesis of ZnFe 2 O 4 nanostructures via a simple hydrothermal route. We have deposited ZnFe 2 O 4 nanostructures on nickel foam substrate at different temperatures to study the correlation between temperature alteration and morphology variation of ZnFe 2 O 4 nanostructures. Also, electrochemical studies were conducted to better understand the supercapacitive behaviour of the effect of temperature and morphology variation on the electrodes. The study consisted of ZnFe 2 O 4 electrode material synthesized at four different temperatures and a change in morphology was monitored. ZnFe 2 O 4 microspheres synthesized at 120℃ exhibit a maximum specific capacitance of 883 F/g at 5 mV/s in 1M KOH with an energy density of 113 Wh/kg and power density of 0.8 kW/kg and a cyclic stability upto 2000 cycles with a retention rate of 85%. Hydrothermal Surface Morphology Temperature Dependence ZnFe2O4 Nanostructures.s Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 1. Introduction Efficient energy storage and management systems are among the basic requirements of today’s world. With the ever-increasing population and globalization, it is to be understood that resources are at a larger toil of extinction. So, more eco-friendly yet quick response alternatives should be explored[ 1 ]. One such invention is supercapacitors which have emerged as a most exploited option in electrochemical energy storage because of their high power density, fast charging discharging time and improved life span as compared to typical batteries[ 2 ]. There are a wide variety of materials which are been developed by research scientists to be used as an electrode material for supercapacitor applications. Electrode material can be classified as EDLC’s Pseudocapacitors and Hybrid supercapacitors based on raw materials employed for synthesis[ 3 ]. There are various zinc-based spinel oxides which exhibit good electrochemical behaviour when all the associated parameters are optimized efficiently[ 4 ]. Herein, we have synthesized ZnFe 2 O 4 electrode material via a hydrothermal route on nickel foam as a substrate. ZnFe 2 O 4 is a binary transition metal oxide which has good electrical conductivity and high electrochemical acitivity as compared to Li-Ion batteries[ 5 ]. One of the key specialities of ZnFe₂O₄ is its ability to undergo reversible redox reactions, which contribute to improved pseudocapacitive behavior. The presence of Fe and Zn in the spinel structure assists rapid charge transfer and ion diffusion, thereby improving the material's charge storage capacity[ 6 ]. Additionally, ZnFe₂O₄ possesses a relatively large surface area, which enhances electrolyte accessibility and increases the number of active sites for electrochemical reactions[ 7 ], [ 8 ]. Hydrothermal method is a facile and scalable technique which is used for synthesis of ZnFe 2 O 4 electrode material.This method has a long list of advantages over conventional methods such as (i) Controllable particle size & morphology (ii) High purity and crystallinity (iii) Enhanced Homogeneity & Uniform Composition (iv) Environmental Friendly[ 9 ], [ 10 ]. Hydrothermal parameters such as time, temperature, pressure can be tuned to enhance the electrochemical behaviour of ZnFe₂O₄ nanostructures[ 11 ], [ 12 ]. As morphology of the material influences the electrochemical behaviour, it is important to develop suitable nanostructures with improved performance[ 13 ], [ 14 ]. From an explicit literature review, in the present work, ZnFe₂O₄ electrode material is synthesized at four different hydrothermal temperatures on nickel foam substrate via a hydrothermal route to observe the effect of temperature variation on the morphology of the ZnFe₂O₄ nanostructures. A significant improvement is observed in the value of specific capacitance and cyclic life with an increase in temperature and a change in the morphology of ZnFe₂O₄ structures. Hence, this study of the effect of temperature on supercapacitive behaviour can be useful for improvising the research and application of ZnFe₂O₄ as an efficient candidate as an electrode material. Table.1. shows the values of electrochemical parameters obtained for all four sets of temperature. 2. Experimental 2.1 Chemicals All the chemicals utilized here were of analytical grade and utilized without any further purification. A nickel foam substrate of dimension 2 × 4 was selected as a current collector for the deposition of active material. Before deposition, the nickel foam was cleansed thoroughly by ultrasonication in 1 M dil. HCl, ethanol, acetone and distilled water for 15 min each. The complete synthesis process was assisted by double distilled water as a solvent. 2.2 Hydrothermal Synthesis of ZnFe₂O₄ For the hydrothermal synthesis of ZnFe 2 O 4 electrodes, 4 mM of ferric nitrate hexahydrate, 2 mM of zinc nitrate hexahydrate, 2 mM of ammonium fluoride and 9 mM of Urea were dissolved in 40 ml distilled water by magnetic stirring for 30 min. The obtained solution along with the cleansed nickel foam substrate was shifted into Teflon lined autoclave. The autoclave was clinched, tightly and the reaction was maintained for four different sets of temperatures which includes 120 ◦C, 140◦C,160◦C & 180◦C for a fixed reaction time of 12 h. After the completion of the reaction, nickel foam substrate deposited with ZnFe 2 O 4 nanostructures was rinsed with distilled water to remove extra active material. The obtained as-prepared electrodes are then dried and calcined at 350 ◦C for 2 h. The mass loading of the deposited active material was obtained as 0.005,0.014,0.012,0.010 mg cm − 2 at 120 ◦C, 140◦C,160◦C & 180◦C respectively. 2.3 Material Characterization The structural properties of ZnFe 2 O 4 electrode material were studied using Proto-AXRD Benchtop Diffractometer (CuKα radiation) with 2θ varying from 10◦ to 80◦. The electrode material's morphological analysis was carried out using a JEOL JSM IT-300 scanning electron microscope (SEM) at an accelerating voltage of 20 kV. Electrochemical analysis & supercapacitive response of the electrode were observed by using various characterization techniques such as Cyclic Voltammetry (CV), Galvanostatic charge-discharge studies (GCD) and Electrochemical Impedance Spectroscopy (EIS) studies. All the electrochemical analysis was conducted using a CHI 660C electrochemical workstation in 3 M KOH as an electrolyte. 3. Results and Discussion 3.1 Structural and Morphological Characterization XRD examination was performed to ascertain the phase purity and crystallinity of the produced electrode material. The XRD profile of ZnFe 2 O 4 nanostructures produced hydrothermally is shown in Fig. 1 . The peaks and patterns shown show that ZnFe 2 O 4 is crystalline. About 30◦, 35.4◦, 40◦, 48◦, 53.2◦, 56.7◦, 65.2◦, and 78◦ are the diffraction peaks in the ZnFe 2 O 4 XRD pattern[ 15 ]. These correspond to crystal planes with Miller indices of (220), (311), (400), (422), (511), (440), (620), and (533)[ 7 ], [ 16 ]. Additionally, two impurity peaks are seen at 44◦ and 68◦, indicating that nickel is present in trace levels. Because of a thin coating of ZnFe 2 O 4 material and reduced mass deposition on nickel foam, there has been a little change in the peak positions and some noise signals. It has been observed that as the temperature increases the noise of the peaks increases XRD pattern at 180℃ is more noisy and gets clearer as approached to 120℃.It can be clearly stated that temperature change has no major effect on XRD studies[ 17 ], [ 18 ]. Lattice parameter calculations also show that hydrothermally produced ZnFe 2 O 4 has a spinel cubic structure, with lattice parameter values of a = b = c = 8.78 Å, which is close to the theoretical value listed in the crystallographic databases[ 19 ]. Surface morphology is a three-dimensional qualitative description of what a surface is whether it is smooth, rough, granular, porous, non-porous, patterned or non-patterned plays an important role in deciding the electrochemical behaviour of the materia[ 20 ], [ 21 ], [ 22 ]l. Figure 2 (a-h) illustrates the different morphologies of ZnFe 2 O 4 nanostructures deposited on nickel foam substrates obtained for different values of temperature ranging from 120℃ to 180℃. ZnFe 2 O 4 nanostructures synthesized at 120℃ show microspheres, and nanocubes are formed at 140℃ followed by nanospheres and nanopetals at 160℃ & 180℃ respectively. On a comparative note it can be visualized that microspheres have large surface area and are deeply packed with increased porosity as compared to the other counterparts. The degree of ion diffusion and electrolyte absorption is on the surface level for petals, spheres and cubes where whereas spheres absorb through deep channels[ 16 ], [ 23 ]. As per literature support, it can be suggested that the variation in temperature affects the crystallization, growth and orientation of crystals during hydrothermal heating. These reasons can be attributed to variations in the nanoarchitecture obtained at different temperatures leading to alteration in specific capacitance values[ 6 ], [ 14 ]. 3.2 Electrochemical Characterization Using 3 M KOH as an electrolyte, the electrochemical analysis of hydrothermally produced and annealed ZnFe 2 O 4 electrode material is examined. The three-electrode setup uses the artificial electrode, standard Ag/AgCl electrode as the reference electrode, graphite electrode as the counter electrode, and electrode as the working electrode (area 2 cm 2 ). Cyclic voltammetry and galvanostatic charged-discharge tests were used to determine the electrode material's specific capacitance values. Electrochemical impedance spectroscopy was used to examine the material's frequency response and cyclic stability. Figure 3 .illustrates the cyclic voltammetry profile of ZnFe 2 O 4 nanostructures ranging from 120℃ to 180℃. The scans were conducted at 5 mV/s within the potential range of 0 V- 0.45 V. Cyclic voltammetry measurements are an efficient tools to determine the specific capacitance of a material by varying its scan rate at various potentials. Herein for comparison purposes, we have shown the cv curve at 5mV/s for 120℃ to 180℃. The cv curves show a quasi-rectangular nature revealing the pseudocapacitive nature of ZnFe 2 O 4 electrode material[ 24 ], [ 25 ]. The good rate capability and stability of the electrode material are indicated by the clear and distinct curves at higher scan speeds[ 26 ].The values of specific capacitance are 883.23 F/g at 120℃,691.94 F/g at 140℃,430.75 F/g at 160℃ and 299.17 F/g at 180℃. The analysis indicates that ZnFe 2 O 4 nanostructures synthesized at 120 ℃ has a maximum specific capacitance as it has maximum area under the curve. Figure 4 . illustrates the galvanostatic charge-discharge curves at four different temperatures ranging from ZnFe 2 O 4 nanostructures ranging from 120℃ to 180℃. The charge discharge profile is recorded for 1mA/cm 2 within the potential range 0-0.45 V. For 180℃ the potential is around 0.3 whereas for 120℃ the potential reaches to about 0.45.The obtained GCD curves indicate super capacitive nature with supercapattery-like behaviour as the curves show a kink at the start of discharge. The current density's potential-dependent change over time demonstrates that capacitive behaviour mostly influences the charge storage mechanism instead of intercalation. As the current density rises, the discharge time falls, which causes the specific capacitance to drop at higher current densities[ 27 ], [ 28 ]. The values of energy density and power density are observed as 113 Wh/kg & 0.8kW/kg at 120℃,40.8 Wh/g & 4 kW/kg at 140℃, 34 Wh/kg & 3.33 kW/kg at 160℃ and 29.14 Wh/kg & 2.85 kW/kg for 180℃ respectively. The coulombic efficiency ranges from 80–85% for all four combinations. The next series of electrochemical properties consist of Fig. 5 . which depicts the reaction between specific capacitance vs. scan rate. It can be visualised that specific capacitance decreases with an increase in scan rate. This effect can be attributed to the fact that at lower scan rates the electrolytes manage to sweep deep into the matrix of electrode material whereas at higher scan rates as the speed increases electroytes and ions just scan the surface leading to a decrease in specific capacitance. Figure 6 . depicts the electrochemical impedance spectroscopy analysis of ZnFe 2 O 4 nanostructures to study the frequency response and capacitive behaviour.The investigation was conducted for ZnFe 2 O 4 nanostructures from 120℃ to 180℃ at a frequency range of 1Hz-100 Hz. Two sections make up the Nyquist plot: a continuous straight line at the end that represents the Warburg slope and a semicircle whose diameter represents the charge transfer resistance, or Rct. The electrode's supercapacitive behavior. Additionally, the electrode's intrinsic resistance in relation to the electrolyte, separator, and current collector resistance is responsible for the equivalent series resistance Rs. The value of Equivalent series resistance (ESR) and constant phase element (CPE) were analysed by fitting the Nyquist plot using Z view software as Rs = 4.43, CPE = 0.035 & Rs = 5.62, CPE = 0.065 & Rs = 6.50 &CPE = 0.1, Rs = 8.95& CPE = 0.15 at 120℃ to 180℃. Figure 7 . shows the cyclic stability studies were conducted for about 2000 cycles at a scan rate of 100mV/s in 3M KOH. The degradation of active material in trace amounts during the continuous charged discharge process is the cause of this retention rate discrepancy.A capacitance retention rate of about 80–95% is observed as the temperature increases from 120℃ to 180℃.With their long-term cyclic stability, ZnFe2O4 nanosheets show promise as supercapacitive electrodes. Table.1. Electrochemical parameters for ZnFe 2 O 4 electrode material. Temperature Morphology Specific Capacitance (F/g) Mass Loading (cm 2 /gm) Energy Density (Wh/kg) Power Density (kW/kg) 120℃ Microspheres 883.23 0.005 113.92 0.8 140℃ Nanocubes 691.94 0.014 40.8 4 160℃ Nanospheres 430.75 0.012 34 3.333333333 180℃ Nanopetals 299.17 0.010 29.14285714 2.857142857 4. Conclusion In the presented work, ZnFe 2 O 4 electrode material is synthesized via a hydrothermal route on nickel foam substrate at four different temperatures by keeping all the other associated reaction parameters constant. ZnFe 2 O 4 are deposited at 120℃,140℃, 160℃ and 180℃ respectively. A series of structural and morphological characterizations are been conducted to confirm the formation of material and to study the role of temperature in altering the morphology of the electrode material. The XRD investigations suggest that ZnFe 2 O 4 nanostructures are crystalline in nature with well-defined peaks. Surface morphology exhibits four different morphologies at four different temperatures namely microsphere, nanocubes, nanospheres and nanopetals at respective temperatures. Also, electrochemical analysis was carried out to study the effect of temperature and morphology on supercapacitive parameters. ZnFe 2 O 4 electrode material at 120℃ displays the maximum specific capacitance of 883.23 F/g at 5mV/s with an energy density of 113.92 Wh/kg and power density of 0.8 kW/kg. To conclude it can be stated that hydrothermal deposition temperature plays a vital role in deciding the morphology of the nanostructures which in turn influences the electrochemical behaviour of the electrode material. This study is of importance for the optimization of electrochemical parameters associated with ZnFe 2 O 4 nanostructures. Declarations Declaration of interests The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Data Availability Statement This study was carried out using publicly available data. All the data and findings are included in the manuscript. Funding Statement The authors did not receive support from any organisation for the submitted work. Consent to Publish- Not applicable Consent to Participate - Not applicable Ethics Declaration- Not applicable Author Contribution Statement: Nidhi Tiwari: Experimentation, Conceptualization, Data collection and data analysis, Methodology, Formal analysis, Investigation, Writing-original draft. Priya Gaikwad : Formal analysis, Suggestions for improvement, Writing and Editing. R.K.Kamat, S .B. Kulkarni : Supervision, Editing. Nidhi Tiwari Thakur College of Engineering and Technology, Kandivali East, Mumbai, Maharashtra 400101, India. [email protected] Priya Gaikwad Materials Research Laboratory, Department of Physics, The Institute of Science, Dr. Homi Bhabha State University, Madam Cama Road, Mumbai, Maharashtra 400032, India. [email protected] R.K. Kamat Materials Research Laboratory, Department of Physics, The Institute of Science, Dr. Homi Bhabha State University, Madam Cama Road, Mumbai, Maharashtra 400032, India. [email protected] Corresponding Author- Shrinivas Kulkarni Materials Research Laboratory, Department of Physics, The Institute of Science, Dr. Homi Bhabha State University, Madam Cama Road, Mumbai, Maharashtra 400032, India corresponding author: [email protected] References Tiwari NG, Kadam SL, Kakade AB, Ingole RS, Kulkarni SB. Synthesis Route Dependent Nanostructured ZnCo 2 O 4 Electrode Material for Supercapacitor Application. ECS J Solid State Sci Technol. 2021;10(10). 10.1149/2162-8777/ac2915 . Wang K, et al. Enhancing the Performance of a Battery-Supercapacitor Hybrid Energy Device through Narrowing the Capacitance Difference between Two Electrodes via the Utilization of 2D MOF-Nanosheet-Derived Ni@Nitrogen-Doped-Carbon Core-Shell Rings as Both Negative and P. ACS Appl Mater Interfaces. 2020;12(42):47482–9. 10.1021/acsami.0c12830 . Tiwari NG, Kadam SL, Kulkarni SB. Synthesis and characterization of ZnCo 2 O 4 electrode for high-performance supercapacitor application. 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Iqbal MZ, Khan J. Optimization of cobalt-manganese binary sulfide for high performance supercapattery devices. Electrochim Acta. 2021;368:137529. 10.1016/j.electacta.2020.137529 . Das A, Raj B, Mohapatra M, Andersen SM, Basu S. Performance and future directions of transition metal sulfide-based electrode materials towards supercapacitor/supercapattery. Wiley Interdiscip Rev Energy Environ. 2022;11(1). 10.1002/wene.414 . Additional Declarations No competing interests reported. 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. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-7019735","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":493165613,"identity":"fc0e4c4b-3f6b-4914-8dd8-7a4decc6b042","order_by":0,"name":"Nidhi Tiwari","email":"","orcid":"","institution":"Thakur College of Engineering and Technology","correspondingAuthor":false,"prefix":"","firstName":"Nidhi","middleName":"","lastName":"Tiwari","suffix":""},{"id":493165614,"identity":"e3d86c5b-71e8-4727-b5f0-5f1978e9e5d7","order_by":1,"name":"Priya Gaikwad","email":"","orcid":"","institution":"The Institute of Science, Dr. Homi Bhabha State University","correspondingAuthor":false,"prefix":"","firstName":"Priya","middleName":"","lastName":"Gaikwad","suffix":""},{"id":493165618,"identity":"b99d6037-118c-4534-8445-236931acc9e4","order_by":2,"name":"R. K. Kamat","email":"","orcid":"","institution":"The Institute of Science, Dr. Homi Bhabha State University","correspondingAuthor":false,"prefix":"","firstName":"R.","middleName":"K.","lastName":"Kamat","suffix":""},{"id":493165619,"identity":"0edfa6de-82f2-4fa7-a82f-5fc0e396bf79","order_by":3,"name":"Shrinivas Kulkarni","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA3klEQVRIiWNgGAWjYDACCTYGZiDFw8DAfICBsYE0LWwJpGkB6TIgTov87La0x4VtdTL8/We+SfzcYSPHwH746AZ8WgzuHDtuPLPtMI/Ejdxtkr1n0owZeNLSbuDVIpHeJs3bdoDHQIJ3mwRv2+HEBgkeM7xa5GeAtdTxGPCfeSb5lxgtDDfSjgG1MAP9nsMmTZQtQL+kG/OcA/klzdhati3NmI2QX4AhZvaYp6zOnr//8MObb9ts5PjZDx/D7zBgFDIwsoEZLBIQLmEAVPMHzGD+QITqUTAKRsEoGIEAAEX1Rg/8qXp6AAAAAElFTkSuQmCC","orcid":"","institution":"The Institute of Science, Dr. Homi Bhabha State University","correspondingAuthor":true,"prefix":"","firstName":"Shrinivas","middleName":"","lastName":"Kulkarni","suffix":""}],"badges":[],"createdAt":"2025-07-01 11:23:22","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7019735/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7019735/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":88044782,"identity":"3868a42a-52d0-4a4a-aece-f370e0ec1cb6","added_by":"auto","created_at":"2025-07-31 18:03:29","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":56690,"visible":true,"origin":"","legend":"\u003cp\u003eXRD analysis of ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4 \u003c/sub\u003e\u0026nbsp;nanostructures at different temperatures.\u003c/p\u003e","description":"","filename":"1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7019735/v1/9e22ca735a46698443e40797.jpg"},{"id":88044781,"identity":"2081a8d9-63bd-48e5-add1-d200a9a53ec2","added_by":"auto","created_at":"2025-07-31 18:03:29","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":235630,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003e(a-h)\u003c/strong\u003e SEM micrographs of ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4 \u003c/sub\u003enanostructures from 120℃ to 180℃.\u003c/p\u003e","description":"","filename":"2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7019735/v1/7259d4af0a530d4059375b26.jpg"},{"id":88044784,"identity":"ff81ed5d-abf6-4efc-b0a2-37ddbc5a89cc","added_by":"auto","created_at":"2025-07-31 18:03:29","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":37673,"visible":true,"origin":"","legend":"\u003cp\u003eCyclic Voltammetry profile of ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4 \u003c/sub\u003enanostructures at 5mV/s Vs. SCE from 120℃ to 180℃.\u003c/p\u003e","description":"","filename":"3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7019735/v1/04780f74b4c83a2c06fc5677.jpg"},{"id":88045335,"identity":"d199fab1-f23d-4aaf-b32e-cc5b54dbf61b","added_by":"auto","created_at":"2025-07-31 18:11:29","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":28106,"visible":true,"origin":"","legend":"\u003cp\u003eGalvanostatic Charge-Discharge curves for ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4 \u003c/sub\u003enanostructures from 120℃ to 180℃.\u003c/p\u003e","description":"","filename":"4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7019735/v1/88d9e72bdc6214bec3429d29.jpg"},{"id":88044799,"identity":"db5dd7a4-d5e6-4da3-a129-3f7b29217742","added_by":"auto","created_at":"2025-07-31 18:03:29","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":34167,"visible":true,"origin":"","legend":"\u003cp\u003eSpecific Capacitance vs. Scan Rate profile for ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4 \u003c/sub\u003enanostructures.\u003c/p\u003e","description":"","filename":"5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7019735/v1/a0b29dbc01bfd063492ba121.jpg"},{"id":88044804,"identity":"4b5b4e30-f290-4563-af95-11689fa5291e","added_by":"auto","created_at":"2025-07-31 18:03:30","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":23528,"visible":true,"origin":"","legend":"\u003cp\u003eNyquist plot for ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4 \u003c/sub\u003eelectrode material in the frequency range 1 Hz–100 H\u003cstrong\u003e \u003c/strong\u003ez.\u003c/p\u003e","description":"","filename":"6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7019735/v1/1f1692cd236e26b11c649766.jpg"},{"id":88046680,"identity":"a5f7150a-e0d8-4436-95c0-0b5459145ac5","added_by":"auto","created_at":"2025-07-31 18:27:29","extension":"jpg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":71802,"visible":true,"origin":"","legend":"\u003cp\u003eCyclic Stability profile for about 2000 cycles\u003c/p\u003e","description":"","filename":"7.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7019735/v1/501b97d3baa510828ceb062f.jpg"},{"id":90502145,"identity":"822ae80b-084d-417f-a883-f4c9b2529530","added_by":"auto","created_at":"2025-09-03 11:53:46","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1150521,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7019735/v1/d85ee714-9b45-48a7-a8ff-58e4afaab9fe.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"\u003cp\u003e\u003cstrong\u003eTemperature-Driven Surface Modifications of Hydrothermally Synthesized ZnFe₂O₄ for High-Efficiency Supercapacitors\u003c/strong\u003e\u003c/p\u003e","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003e\u003cdiv class=\"BlockQuote\"\u003e\u003cp\u003eEfficient energy storage and management systems are among the basic requirements of today\u0026rsquo;s world. With the ever-increasing population and globalization, it is to be understood that resources are at a larger toil of extinction. So, more eco-friendly yet quick response alternatives should be explored[\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. One such invention is supercapacitors which have emerged as a most exploited option in electrochemical energy storage because of their high power density, fast charging discharging time and improved life span as compared to typical batteries[\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. There are a wide variety of materials which are been developed by research scientists to be used as an electrode material for supercapacitor applications. Electrode material can be classified as EDLC\u0026rsquo;s Pseudocapacitors and Hybrid supercapacitors based on raw materials employed for synthesis[\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. There are various zinc-based spinel oxides which exhibit good electrochemical behaviour when all the associated parameters are optimized efficiently[\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eHerein, we have synthesized ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e electrode material via a hydrothermal route on nickel foam as a substrate. ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e is a binary transition metal oxide which has good electrical conductivity and high electrochemical acitivity as compared to Li-Ion batteries[\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. One of the key specialities of ZnFe₂O₄ is its ability to undergo reversible redox reactions, which contribute to improved pseudocapacitive behavior. The presence of Fe and Zn in the spinel structure assists rapid charge transfer and ion diffusion, thereby improving the material's charge storage capacity[\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. Additionally, ZnFe₂O₄ possesses a relatively large surface area, which enhances electrolyte accessibility and increases the number of active sites for electrochemical reactions[\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e], [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Hydrothermal method is a facile and scalable technique which is used for synthesis of ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e electrode material.This method has a long list of advantages over conventional methods such as (i) Controllable particle size \u0026amp; morphology (ii) High purity and crystallinity (iii) Enhanced Homogeneity \u0026amp; Uniform Composition (iv) Environmental Friendly[\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e], [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. Hydrothermal parameters such as time, temperature, pressure can be tuned to enhance the electrochemical behaviour of ZnFe₂O₄ nanostructures[\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e], [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. As morphology of the material influences the electrochemical behaviour, it is important to develop suitable nanostructures with improved performance[\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e], [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eFrom an explicit literature review, in the present work, ZnFe₂O₄ electrode material is synthesized at four different hydrothermal temperatures on nickel foam substrate via a hydrothermal route to observe the effect of temperature variation on the morphology of the ZnFe₂O₄ nanostructures. A significant improvement is observed in the value of specific capacitance and cyclic life with an increase in temperature and a change in the morphology of ZnFe₂O₄ structures. Hence, this study of the effect of temperature on supercapacitive behaviour can be useful for improvising the research and application of ZnFe₂O₄ as an efficient candidate as an electrode material.\u003cb\u003eTable.1.\u003c/b\u003e shows the values of electrochemical parameters obtained for all four sets of temperature.\u003c/p\u003e\u003c/div\u003e\u003c/p\u003e"},{"header":"2. Experimental","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003e2.1 Chemicals\u003c/h2\u003e\u003cp\u003e\u003cdiv class=\"BlockQuote\"\u003e\u003cp\u003eAll the chemicals utilized here were of analytical grade and utilized without any further purification. A nickel foam substrate of dimension 2 \u0026times; 4 was selected as a current collector for the deposition of active material. Before deposition, the nickel foam was cleansed thoroughly by ultrasonication in 1 M dil. HCl, ethanol, acetone and distilled water for 15 min each. The complete synthesis process was assisted by double distilled water as a solvent.\u003c/p\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\u003ch2\u003e2.2 Hydrothermal Synthesis of ZnFe₂O₄\u003c/h2\u003e\u003cp\u003e\u003cdiv class=\"BlockQuote\"\u003e\u003cp\u003eFor the hydrothermal synthesis of ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e electrodes, 4 mM of ferric nitrate hexahydrate, 2 mM of zinc nitrate hexahydrate, 2 mM of ammonium fluoride and 9 mM of Urea were dissolved in 40 ml distilled water by magnetic stirring for 30 min. The obtained solution along with the cleansed nickel foam substrate was shifted into Teflon lined autoclave. The autoclave was clinched, tightly and the reaction was maintained for four different sets of temperatures which includes 120 ◦C, 140◦C,160◦C \u0026amp; 180◦C for a fixed reaction time of 12 h. After the completion of the reaction, nickel foam substrate deposited with ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e nanostructures was rinsed with distilled water to remove extra active material. The obtained as-prepared electrodes are then dried and calcined at 350 ◦C for 2 h. The mass loading of the deposited active material was obtained as 0.005,0.014,0.012,0.010 mg cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e at 120 ◦C, 140◦C,160◦C \u0026amp; 180◦C respectively.\u003c/p\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\u003ch2\u003e2.3 Material Characterization\u003c/h2\u003e\u003cp\u003e\u003cdiv class=\"BlockQuote\"\u003e\u003cp\u003eThe structural properties of ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e electrode material were studied using Proto-AXRD Benchtop Diffractometer (CuKα radiation) with 2θ varying from 10◦ to 80◦. The electrode material's morphological analysis was carried out using a JEOL JSM IT-300 scanning electron microscope (SEM) at an accelerating voltage of 20 kV. Electrochemical analysis \u0026amp; supercapacitive response of the electrode were observed by using various characterization techniques such as Cyclic Voltammetry (CV), Galvanostatic charge-discharge studies (GCD) and Electrochemical Impedance Spectroscopy (EIS) studies. All the electrochemical analysis was conducted using a CHI 660C electrochemical workstation in 3 M KOH as an electrolyte.\u003c/p\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e"},{"header":"3. Results and Discussion","content":"\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e\u003ch2\u003e3.1 Structural and Morphological Characterization\u003c/h2\u003e\u003cp\u003eXRD examination was performed to ascertain the phase purity and crystallinity of the produced electrode material. The XRD profile of ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e nanostructures produced hydrothermally is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. The peaks and patterns shown show that ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e is crystalline. About 30◦, 35.4◦, 40◦, 48◦, 53.2◦, 56.7◦, 65.2◦, and 78◦ are the diffraction peaks in the ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e XRD pattern[\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. These correspond to crystal planes with Miller indices of (220), (311), (400), (422), (511), (440), (620), and (533)[\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e], [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. Additionally, two impurity peaks are seen at 44◦ and 68◦, indicating that nickel is present in trace levels. Because of a thin coating of ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e material and reduced mass deposition on nickel foam, there has been a little change in the peak positions and some noise signals. It has been observed that as the temperature increases the noise of the peaks increases XRD pattern at 180℃ is more noisy and gets clearer as approached to 120℃.It can be clearly stated that temperature change has no major effect on XRD studies[\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e], [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. Lattice parameter calculations also show that hydrothermally produced ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e has a spinel cubic structure, with lattice parameter values of a\u0026thinsp;=\u0026thinsp;b\u0026thinsp;=\u0026thinsp;c\u0026thinsp;=\u0026thinsp;8.78 \u0026Aring;, which is close to the theoretical value listed in the crystallographic databases[\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e].\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"BlockQuote\"\u003e\u003cp\u003eSurface morphology is a three-dimensional qualitative description of what a surface is whether it is smooth, rough, granular, porous, non-porous, patterned or non-patterned plays an important role in deciding the electrochemical behaviour of the materia[\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e], [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e], [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]l. Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e \u003cb\u003e(a-h)\u003c/b\u003e illustrates the different morphologies of ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e nanostructures deposited on nickel foam substrates obtained for different values of temperature ranging from 120℃ to 180℃. ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e nanostructures synthesized at 120℃ show microspheres, and nanocubes are formed at 140℃ followed by nanospheres and nanopetals at 160℃ \u0026amp; 180℃ respectively. On a comparative note it can be visualized that microspheres have large surface area and are deeply packed with increased porosity as compared to the other counterparts. The degree of ion diffusion and electrolyte absorption is on the surface level for petals, spheres and cubes where whereas spheres absorb through deep channels[\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e], [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. As per literature support, it can be suggested that the variation in temperature affects the crystallization, growth and orientation of crystals during hydrothermal heating. These reasons can be attributed to variations in the nanoarchitecture obtained at different temperatures leading to alteration in specific capacitance values[\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e], [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e].\u003c/p\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\u003ch2\u003e3.2 Electrochemical Characterization\u003c/h2\u003e\u003cp\u003e\u003cdiv class=\"BlockQuote\"\u003e\u003cp\u003eUsing 3 M KOH as an electrolyte, the electrochemical analysis of hydrothermally produced and annealed ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e electrode material is examined. The three-electrode setup uses the artificial\u003c/p\u003e\u003cp\u003eelectrode, standard Ag/AgCl electrode as the reference electrode, graphite electrode as the counter electrode, and electrode as the working electrode (area 2 cm\u003csup\u003e2\u003c/sup\u003e). Cyclic voltammetry and galvanostatic charged-discharge tests were used to determine the electrode material's specific capacitance values. Electrochemical impedance spectroscopy was used to examine the material's frequency response and cyclic stability.\u003c/p\u003e\u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e.illustrates the cyclic voltammetry profile of ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e nanostructures ranging from 120℃ to 180℃. The scans were conducted at 5 mV/s within the potential range of 0 V- 0.45 V. Cyclic voltammetry measurements are an efficient tools to determine the specific capacitance of a material by varying its scan rate at various potentials. Herein for comparison purposes, we have shown the cv curve at 5mV/s for 120℃ to 180℃. The cv curves show a quasi-rectangular nature revealing the pseudocapacitive nature of ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e electrode material[\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e], [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. The good rate capability and stability of the electrode material are indicated by the clear and distinct curves at higher scan speeds[\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e].The values of specific capacitance are 883.23 F/g at 120℃,691.94 F/g at 140℃,430.75 F/g at 160℃ and 299.17 F/g at 180℃. The analysis indicates that ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e nanostructures synthesized at 120 ℃ has a maximum specific capacitance as it has maximum area under the curve.\u003c/p\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"BlockQuote\"\u003e\u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. illustrates the galvanostatic charge-discharge curves at four different temperatures ranging from ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e nanostructures ranging from 120℃ to 180℃. The charge discharge profile is recorded for 1mA/cm\u003csup\u003e2\u003c/sup\u003e within the potential range 0-0.45 V. For 180℃ the potential is around 0.3 whereas for 120℃ the potential reaches to about 0.45.The obtained GCD curves indicate super capacitive nature with supercapattery-like behaviour as the curves show a kink at the start of discharge. The current density's potential-dependent change over time demonstrates that capacitive behaviour mostly influences the charge storage mechanism instead of intercalation. As the current density rises, the discharge time falls, which causes the specific capacitance to drop at higher current densities[\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e], [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. The values of energy density and power density are observed as 113 Wh/kg \u0026amp; 0.8kW/kg at 120℃,40.8 Wh/g \u0026amp; 4 kW/kg at 140℃, 34 Wh/kg \u0026amp; 3.33 kW/kg at 160℃ and 29.14 Wh/kg \u0026amp; 2.85 kW/kg for 180℃ respectively. The coulombic efficiency ranges from 80\u0026ndash;85% for all four combinations.\u003c/p\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"BlockQuote\"\u003e\u003cp\u003eThe next series of electrochemical properties consist of Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e. which depicts the reaction between specific capacitance vs. scan rate. It can be visualised that specific capacitance decreases with an increase in scan rate. This effect can be attributed to the fact that at lower scan rates the electrolytes manage to sweep deep into the matrix of electrode material whereas at higher scan rates as the speed increases electroytes and ions just scan the surface leading to a decrease in specific capacitance.\u003c/p\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e. depicts the electrochemical impedance spectroscopy analysis of ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e nanostructures to study the frequency response and capacitive behaviour.The investigation was conducted for ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e nanostructures from 120℃ to 180℃ at a frequency range of 1Hz-100 Hz. Two sections make up the Nyquist plot: a continuous straight line at the end that represents the Warburg slope and a semicircle whose diameter represents the charge transfer resistance, or Rct. The electrode's supercapacitive behavior. Additionally, the electrode's intrinsic resistance in relation to the electrolyte, separator, and current collector resistance is responsible for the equivalent series resistance Rs. The value of Equivalent series resistance (ESR) and constant phase element (CPE) were analysed by fitting the Nyquist plot using Z view software as Rs\u0026thinsp;=\u0026thinsp;4.43, CPE\u0026thinsp;=\u0026thinsp;0.035 \u0026amp; Rs\u0026thinsp;=\u0026thinsp;5.62, CPE\u0026thinsp;=\u0026thinsp;0.065 \u0026amp; Rs\u0026thinsp;=\u0026thinsp;6.50 \u0026amp;CPE\u0026thinsp;=\u0026thinsp;0.1, Rs\u0026thinsp;=\u0026thinsp;8.95\u0026amp; CPE\u0026thinsp;=\u0026thinsp;0.15 at 120℃ to 180℃.\u003c/p\u003e\u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e. shows the cyclic stability studies were conducted for about 2000 cycles at a scan rate of 100mV/s in 3M KOH. The degradation of active material in trace amounts during the continuous charged discharge process is the cause of this retention rate discrepancy.A capacitance retention rate of about 80\u0026ndash;95% is observed as the temperature increases from 120℃ to 180℃.With their long-term cyclic stability, ZnFe2O4 nanosheets show promise as supercapacitive electrodes.\u003c/p\u003e\u003cp\u003e\u003cb\u003eTable.1.\u003c/b\u003e Electrochemical parameters for ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e electrode material.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"No\" id=\"Taba\" border=\"1\"\u003e\u003ccolgroup cols=\"6\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eTemperature\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eMorphology\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eSpecific Capacitance (F/g)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eMass Loading (cm\u003csup\u003e2\u003c/sup\u003e/gm)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eEnergy Density (Wh/kg)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003ePower Density (kW/kg)\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e120℃\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eMicrospheres\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e883.23\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.005\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e113.92\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e0.8\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e140℃\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eNanocubes\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e691.94\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.014\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e40.8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e160℃\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eNanospheres\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e430.75\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.012\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e34\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e3.333333333\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e180℃\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eNanopetals\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e299.17\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.010\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e29.14285714\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e2.857142857\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003e\u003cdiv class=\"BlockQuote\"\u003e\u003cp\u003eIn the presented work, ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e electrode material is synthesized via a hydrothermal route on nickel foam substrate at four different temperatures by keeping all the other associated reaction parameters constant. ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e are deposited at 120℃,140℃, 160℃ and 180℃ respectively. A series of structural and morphological characterizations are been conducted to confirm the formation of material and to study the role of temperature in altering the morphology of the electrode material. The XRD investigations suggest that ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e nanostructures are crystalline in nature with well-defined peaks. Surface morphology exhibits four different morphologies at four different temperatures namely microsphere, nanocubes, nanospheres and nanopetals at respective temperatures. Also, electrochemical analysis was carried out to study the effect of temperature and morphology on supercapacitive parameters. ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e electrode material at 120℃ displays the maximum specific capacitance of 883.23 F/g at 5mV/s with an energy density of 113.92 Wh/kg and power density of 0.8 kW/kg. To conclude it can be stated that hydrothermal deposition temperature plays a vital role in deciding the morphology of the nanostructures which in turn influences the electrochemical behaviour of the electrode material. This study is of importance for the optimization of electrochemical parameters associated with ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e nanostructures.\u003c/p\u003e\u003c/div\u003e\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eDeclaration of interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData Availability Statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis study was carried out using publicly available data. All the data and findings are included in the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding Statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors did not receive support from any organisation for the submitted work.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent to Publish-\u0026nbsp;\u003c/strong\u003eNot applicable\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent to Participate\u003c/strong\u003e\u003cstrong\u003e-\u0026nbsp;\u003c/strong\u003eNot applicable\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics Declaration-\u0026nbsp;\u003c/strong\u003eNot applicable\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor Contribution Statement:\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eNidhi Tiwari:\u003c/strong\u003e Experimentation, Conceptualization, Data collection and data analysis, Methodology, Formal analysis, Investigation, Writing-original draft. \u003cstrong\u003ePriya Gaikwad :\u003c/strong\u003eFormal analysis, Suggestions for improvement, Writing and Editing. \u003cstrong\u003eR.K.Kamat, S\u003c/strong\u003e\u003cstrong\u003e.B. Kulkarni :\u003c/strong\u003eSupervision, Editing.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eNidhi Tiwari\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThakur College of Engineering and Technology, Kandivali East, Mumbai, Maharashtra 400101, India.\u003c/p\u003e\n\u003cp\u003e\u003cem\[email protected]\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ePriya Gaikwad\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eMaterials Research Laboratory, Department of Physics, The Institute of Science, Dr. Homi Bhabha State University, Madam Cama Road, Mumbai, Maharashtra 400032, India.\u003c/p\u003e\n\u003cp\u003e\u003cem\[email protected]\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003cstrong\u003eR.K. Kamat\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eMaterials Research Laboratory, Department of Physics, The Institute of Science, Dr. Homi Bhabha State University, Madam Cama Road, Mumbai, Maharashtra 400032, India.\u003c/p\u003e\n\u003cp\u003e\u003cem\[email protected]\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCorresponding Author- Shrinivas Kulkarni\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eMaterials Research Laboratory, Department of Physics, The Institute of Science, Dr. Homi Bhabha State University, Madam Cama Road, Mumbai, Maharashtra 400032, India\u003c/p\u003e\n\u003cp\u003e\u003cem\u003ecorresponding author:\u003c/em\u003e\u003cem\[email protected]\u003c/em\u003e\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eTiwari NG, Kadam SL, Kakade AB, Ingole RS, Kulkarni SB. 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Wiley Interdiscip Rev Energy Environ. 2022;11(1). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1002/wene.414\u003c/span\u003e\u003cspan address=\"10.1002/wene.414\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"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":"Hydrothermal, Surface Morphology, Temperature Dependence, ZnFe2O4 Nanostructures.s","lastPublishedDoi":"10.21203/rs.3.rs-7019735/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7019735/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eIn this paper, we demonstrate the synthesis of ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4 \u003c/sub\u003enanostructures via a simple hydrothermal route. We have deposited ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e nanostructures on nickel foam substrate at different temperatures to study the correlation between temperature alteration and morphology variation of ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e nanostructures. Also, electrochemical studies were conducted to better understand the supercapacitive behaviour of the effect of temperature and morphology variation on the electrodes. The study consisted of ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u0026nbsp; \u003c/sub\u003eelectrode material synthesized at four different temperatures and a change in morphology was monitored. ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4 \u003c/sub\u003emicrospheres synthesized at 120℃ exhibit a maximum specific capacitance of 883 F/g at 5 mV/s in 1M KOH with an energy density of 113 Wh/kg and power density of 0.8 kW/kg and a cyclic stability upto 2000 cycles with a retention rate of 85%.\u003c/p\u003e","manuscriptTitle":"Temperature-Driven Surface Modifications of Hydrothermally Synthesized ZnFe₂O₄ for High-Efficiency Supercapacitors","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-07-31 18:03:24","doi":"10.21203/rs.3.rs-7019735/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":"606888fc-05e9-46ca-abb8-19832b10b331","owner":[],"postedDate":"July 31st, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-09-03T11:53:18+00:00","versionOfRecord":[],"versionCreatedAt":"2025-07-31 18:03:24","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7019735","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7019735","identity":"rs-7019735","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}