Microwave synthesis of cobalt vanadium oxide nanospheres: Boosting charge storage capacity with the addition of graphitic carbon nitride nanostructures

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Shanmugapriya, J. Johnson William, B. Saravanakumar, K. Somasundaram This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7307372/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 10 You are reading this latest preprint version Abstract The development of high-performance electrode materials is critical for enhancing the energy storage capabilities of supercapacitors. In this study, cobalt vanadium oxide and its graphitic carbon nitride composites were synthesized and investigated as an electrode material for supercapacitors. The green chemistry, microwave method was employed for the preparation of nanocomposites. The XRD analysis results indicate that the cobalt vanadium oxides are in a poor crystalline nature. The formation of nanosphere shaped morphology is found in the FESEM analysis. The addition of graphitic carbon nitride benefits in the formation of uniformly distributed cobalt vanadium oxide nanospheres. The valance states of the elements presented in the prepared composite were examined using XPS technique. Half-cell mode was employed to assess the charge storage process of the prepared materials. The electrodes of the prepared materials store energy through the pseudocapacitive nature. The electrodes of cobalt vanadium oxide, consisted of 5 wt.% graphitic carbon nitride yields maximum capacity of 380 C g –1 and it is 226% higher than the pristine cobalt vanadium oxide electrodes. Besides, full-cell was devised using activated carbon as the counter electrode. The assembled device could yield maximum specific energy of 25 W h kg –1 at a rate of 815 W kg –1 . Moreover, 12% of energy was found to be retained when rate of delivery is increased to 7.8 fold. All the studies represent that the graphitic carbon nitride added cobalt vanadium oxide nanospheres are suitable materials for the construction of supercapacitors. cobalt vanadium oxide graphitic carbon nitride nanospheres pseudocapacitive-type asymmetric cell Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 1. Introduction Global demand for energy storage devices is intensifying in every year. Energy storage devices like batteries and supercapacitors serve as a pivotal platform for the trending development of EV vehicles and portable electronic devices. Its power density and energy density mitigate the power variations, elevates the system flexibility and enhances the storage capacity. Currently, researches were marching towards supercapacitors due to its large efficiency. Some other attractive features of supercapacitors like high capacitance value, high power density, operation over wider range of temperature and high durability were also gained attention among other energy storage devices [ 1 ]. The role of supercapacitors in automobile and transport systems, defence and military, computers and backup chips, medical, and industrial sectors has been reviewed by Muzaffar et al [ 2 ]. Electric double layer capacitors, pseudocapacitors and hybrid supercapacitor are the classifications of supercapacitors based on their storage capacity. The charge is electrostatically stored by adsorption of ions at the surface of the electrode in EDLC whereas in pseudocapacitors, the charges are stored electrochemically by rapid redox reactions [ 3 ]. The energy storage capacity of pseudocapacitors is far greater than the electric double layer capacitors due to the nature of electrode materials used in their assembly. Transition metal-based compounds are widely used as active materials for supercapacitors. Among, cobalt vanadium oxide is a promising material for various electrochemical applications due to its unique redox characteristics, structural stability, and versatile oxidation states. It exhibits intriguing electrochemical properties that make it valuable in applications such as lithium-ion batteries, supercapacitors, and electrochemical sensors. cobalt vanadium oxide demonstrates a robust ability to undergo reversible redox reactions involving both cobalt and vanadium ions, which contribute significantly to its high specific capacity and excellent energy storage potential. These redox reactions involve the transformation between multiple oxidation states, including Co 2+/3+ and V 3+/5+ , which enhances its electrochemical activity. The presence of both cobalt and vanadium also contributes to a synergistic effect that improves the overall electronic conductivity and stability of the oxide, enhancing charge storage and electron transfer processes. Furthermore, its high theoretical capacity, attributed to multiple electron transfer processes, enables cobalt vanadium oxide to maintain high charge and discharge rates, which is essential for high-performance energy storage applications. Besides, studies indicate that cobalt vanadium oxide anodes suffer to sustain performance during prolonged cycling. To address this, researchers have explored nanostructured cobalt vanadium oxide or its composites with carbonaceous materials to improve cycling stability and electrical conductivity. Currently, graphitic carbon nitride nanostructures are emerged as an efficient material to enhance the electrochemical performance of the metal oxides when the graphitic carbon nitride nanostructures are added in the preparation of composites [ 4 ][ 5 ][ 6 ][ 7 ][ 8 ][ 9 ][ 10 ]. Moreover, graphitic carbon nitride nanostructures is a desirable material due to its large nitrogen content, large surface area, lower impedance, tuneable structure and higher potential for electrode applications [ 7 ]. The semiconductor nature of graphitic carbon nitride exhibits excellent catalytic activity for various reactions like oxygen reduction [ 11 ][ 12 ], hydrogen production [ 13 ][ 14 ], photo-catalytic [ 15 ], electrochemical sensing [ 16 ] and electrochemical energy storage [ 17 ]. The polymer matrix of graphitic carbon nitride builds it to be economical and non-toxic electrode materials for wider applications. The facile synthesis by thermal polymerization using nitrogen rich precursors like cyanamide, melamine, dicyandiamide, thiourea, ammonium thiocyanate, and urea is one of the main attractive features of graphitic carbon nitride. Owing to the nature of these efficient features, GCN nanostructures are incorporated into the metal oxide nanostructures to elevate the charge storage performance. It is worth to mention that the GCN grafted transition metal oxides material has larger surface area and more active sites at the electrode-electrolyte interface, which facilitates the ionic diffusion, thus enhancing the faradaic reaction and the supercapacitor performance [ 18 ]. In the present work, we have prepared the binary transition metal oxide (Cobalt vanadium oxide) composites grafted with graphitic carbon nitride through simple and effective microwave oven method. XRD analysis was carried out to study the structural properties. SEM analysis was made to examine the morphological nature of prepared samples. The chemical composition of sample surface was revealed by XPS analysis. The electrochemical properties of the samples were analysed using three electrode system. 2. Experimental 2.1. Preparation of Graphitic carbon nitride integrated Cobalt Vanadium oxide nanostructures: Graphitic carbon nitride added cobalt vanadium oxide nanomaterials were prepared through microwave oven technique. In 180 ml of double distilled water, 10 wt.% of CTAB was dissolved and stirred continuously. 0.5238 g of cobalt (II) nitrate hexahydrate and 0.4211 g of ammonium metavanadate were dissolved in the solution containing 10 Wt.% of CTAB. Further, different weight per cent of gaphitic carbon nitride (2.5, 5 and 7.5 wt.%) was added to the above blended solution and continuously stirred to obtain a homogenous solution. Besides, 1 M NaOH was prepared and gradually added to the resultant solution to adjust the pH to 10. The final resultant solution was treated at power of 360 W, microwave energy for 10 minutes. Finally, the precipitate was washed with distilled water and dried at 60°C for 12 hours. The as-formed particles were calcined for one hour at 300°C and named as CV2.5GC, CV5GC and CV7.5GC for the cobalt vanadium oxide comprised of 2.5, 5 and 7.5 wt.% of graphitic carbon nitride. Similarly, the pristine cobalt vanadium oxide nanostructures were prepared using same procedure without the addition of graphitic carbon nitride and named as CV. 2.2 Characterization techniques The detailed specifications of the instruments used to characterize the structural, morphological and electrochemical analysis are discussed in the supporting information S1 and S2. 3. Result and discussions 3.1 Structural analysis The structural characterization of prepared nanomaterials was detected using X-Ray Diffractometer spectroscopy (XRD). Figure 1 demonstrates the diffractograms of the prepared materials, indicating the poor crystalline nature. Incorporation of graphitic carbide does not make significant impact on the XRD profile of cobalt vanadium oxides and all the samples remain in the amorphous nature. Besides, XPS analysis was made to examine the valance states of the prepared materials and their results are shown in Fig. 2 . The survey scan of the composite in Fig. 2 a indicates the presence of Co 2p, V 2p, O 1s and C 1s. The wide-angle spectrum of V 2p element is shown in Fig. 2 b, exhibiting multiple peaks at 517.15, 518.29, 524.19 and 525.27 eV and it corresponds to the V 5+ of V 2 O 5 , V 4+ of VO 2 and their corresponding satellites respectively, indicating that the vanadium element is existed in its oxidation states of + 4 and + 5. Figure 2 c shows the highly resolved XPS spectrum of Co 2p element. The obtained spectrum was fitted with the various centered at 780.88, 782.26, 787.29, 791.33, 797.35 and 803.47 eV, indicating the presence of Co 2+ of 2p 3/2 , Co 3+ of 2p 3/2 , satellite of Co 3+ , satellite of Co 2+ , satellite of Co 3+ , Co 2+ of 2p 1/2 and satellite of Co 3+ respectively [ 19 ][ 20 ][ 21 ]. The chemical environment of oxygen element is assessed using its deconvoluted profile (Figure d). The peaks found at 530.3 and 531 eV indicate the lattice oxygen or in a metal-oxygen bond [ 22 ][ 23 ]. The presence of oxygen vacancies is identified from the XPS line centered at 532 eV. Moreover, the peak positioned at 533 eV signifies the existence of surface adsorbed species. Figure 2 e demonstrates the deconvoluted XPS spectrum of C 1s element. The peaks positioned at 284.92 and 285.66 eV represents the sp 2 hybridized graphitic carbon (C-C/C = C) and carbon bonded to nitrogen in g-C 3 N 4 , respectively. The presence of oxygenated and amide type bonding in g-C 3 N 4 is observed from the peaks, located at 286.58 and 287.45 eV respectively [ 24 ]. The XPS line, centered at 288.46 and 289.54 eV reveals formation of N-C = N/C = O bond and carbonated (O = C-O) species in the prepared composites [ 25 ]. Besides, the wide-angle spectrum of N 1s element is shown in Fig. 2 f, displaying XPS line at a binding energy of 397.23, 400.15 and 403.68 eV and it corresponds to the sp2 hybridized nitrogen (C = N-C), sp3 hybridized nitrogen (C-N-C) and oxidized nitrogen species respectively. 3.2. Morphological analysis The surface morphology of prepared materials was analyzed using field emission scanning electron microscopy (FESEM). FESEM images of pristine and graphitic carbon nitride incorporated cobalt vanadium oxide nanostructures are shown in Fig. 3 . All the samples display the spherical shaped particles with the size in the range of nanometer. Moreover, the particles are formed in a uniform manner. The addition of graphitic carbon nitride has found to be influenced in the cobalt vanadium oxide particle size and it could be clearly seen from the Fig. 3 b-c. The size of the particles is reduced when the concentration of graphitic carbon nitride is increased to 5wt.% (Fig. 3 c) and size is increased for further increasing the concentration of graphitic carbon nitride to 7.5 wt.% (Fig. 3 d). Thus, cobalt vanadium oxide nanospheres prepared under the medium of 5 wt.% graphitic carbon nitrides are uniformly distributed with the size smaller than the other samples. Hence, 5 wt.% graphitic carbon nitrides are suitable concentration for the preparation of uniform sized cobalt vanadium oxide particles. 3.3 Analysis of supercapacitive performance The supercapacitor performance of graphitic carbon incorporated cobalt vanadium oxide electrodes was studied using three-electrode electrochemical cell in 2 M aqueous KOH solution. The electrochemical performance was analysed using time domain and frequency domain. The cyclic voltammetry and galvanostatic charge-discharge measurement were based on time domain whereas impedance analysis relies on frequency domain. The CV measurements were carried out within the potential window between − 0.5 to 0.25 V at various scan rates, ranged from 5 to 100 mV s − 1 and their results are displayed in supporting Figure S1 , 4 a and b. The CV curves of all the samples portray non-rectangular shapes displaying strong redox peaks. The swift of anodic and cathodic peaks towards the higher and lower potential, respectively, is observed while increasing the scan rates, which is attributed to Faradaic behaviour [ 26 ]. During forward scan, the electrode is oxidised with the removal of electron (Co 0 - Co 2+ ) and it is represented by the anodic peak at higher potential. Similarly, reverse scan, the electron is added (Co 2+ - Co 0 ) to the electrode materials, indicating by the cathodic peak at lower potential. The oxidation peak during charging process portrays the energy storing capacity while during discharge process, the reduction peak reveals the energy releasing process. The area under the CV curves for graphitic carbon grafted cobalt vanadium oxide electrode was found to be higher than the area encircled by pristine cobalt vanadium oxide. This observation indicates that the inclusion of graphitic carbon enhances the electrochemical performance of cobalt vanadium oxides. The CV curve depicts the appreciable reversibility and high-rate capability at the interface of electrode and electrolyte. The specific capacities are calculated using an Eq. 1 and it is given in a supporting information S4. The estimated specific capacities of all the samples is given in the supporting table S4. The specific capacity of 224, 225, 301 and 235 C g –1 is estimated at a scan rate of 5 mV s –1 for the electrodes of CV, CV2.5GC, CV5GC and CV7.5GC respectively. The electrodes of CV5GC exhibit superior specific capacity when compared to other electrodes. This may be due to the enhanced EDLC behaviour with the inclusion of graphitic carbon leading to the increased current density. Moreover, the charge storage capacity was found to be degrading when the scan rate reaches infinity and it may be due to the lesser diffusion time of electrolyte ions [ 27 ]. To further investigate the electrochemical properties of sample, galvanostatic charge-discharge analysis was conducted within the potential window of -0.5 to 0.25 V. The study was carried out at different specific currents and their results are displayed in the supporting Figure S2 and 4c, demonstrating the non-linear behaviour for all electrodes. This nature portrays that the prepared materials exhibit excellent faradic behaviour for storing appreciable charges. The GCD studies also reveal that CV5GC electrode encircles larger discharge area, illustrating the enhanced supercapacitor performance than the other electrodes. The specific capacity (Fig. 4 d) of all the electrodes was calculated using the Eq. 2 and it is given in supporting information S4. The specific capacities of all electrodes are estimated and it is given in the supporting table S6. The specific capacity of CV, CV2.5GC, CV5GC and CV7.5GC electrodes is estimated and it found to be 168, 179, 380 and 236 C g –1 respectively. The addition of graphitic carbide has significantly improved the charge storage performance, resulting in an enhancement of specific capacity. A maximum of 380 C g –1 is estimated for cobalt vanadium oxide electrode consisted of 5 wt.% of graphitic carbide nanostructures. Moreover, the specific capacity is found to be decreased on increasing the current density and it is due to less time find for electrolyte ions to diffuse into the electrode materials [ 28 ]. The electrochemical impedance spectroscopy was implemented to study the charge transport characteristics of the prepared electrodes. A frequency range of 0.01 Hz to 100 kHz is used to analyse the electrochemical performance of the electrodes. The obtained impedance spectra were fitted to the modified Randle’s circuit (inset of Fig. 4 e). Generally, the Nyquist plot consists of a semicircle in the high frequency region and inclined spike in the low frequency region. The presence of semicircle signifies the electrochemical reactions prevailing at the electrode/electrolyte interface. The inclined spike in the low frequency indicates the diffusive nature of OH − ions into the matrix of electrodes. The ohmic resistance between the solution and electrode is obtained from the point of intersection between the real axis and the curve and the charge transfer resistance is estimated from the radius of semicircle arc. The inclined spike in the low frequency region is related to the diffusion impedance (Warburg impedance, Z W ) [ 22 ]. The solution and charge transfer resistance is obtained for all the samples from the X-intercept and diameter of the semi-circle. The solution resistance of 3.54, 1.03, 0.968 and 1.549 Ω and charge transfer resistance of 3.17, 0.56, 0.37 and 0.78 Ω is obtained for the electrodes of CV, CV2.5GC, CV5GC and CV7.5GC, respectively. The stability of CV and CV5GC electrodes was examined for 5000 continuous cycles at a current density of 15 A g –1 . The capacity retention is evaluated for each 100 cycles (Fig. 4 f). The retention of 74 and 92% is found to be retained for the electrodes of pristine and graphitic carbide added cobalt vanadium oxide nanostructures, respectively even after 5000 GCD cycles. The increase in retention is mainly due to the opening of channels on continuous cycling which enhances the electroactive sites in the composites. The diffusion of electrolyte ions within the material is increased as the huge electroactive sites were been triggered leading to the intensified electrochemical performance. Also, during the continuous cycling, wetting of the particles provides the huge new channels which trails the better access of sites for storing charges. < Figure 5 . Assessment of ASCs energy storage characteristics: (a) CV, (b) GCD, (c) C S versus I D , (d) Ragone plot, (e) Nyquist plot and (f) lifespan analysis 3.4 Assessment of two electrode system Besides, full cell is assembled by employing the cobalt vanadium oxide comprised of 5wt.% of graphitic carbon nitride as the counter electrode to the activated carbon. The measurement was done at an operating voltage of 1.4 V. Figure 5 shows the results of electrochemical performance of fabricated device, exhibiting the pseudocapacitive nature (Fig. 5 a&b) of energy storage process. The specific capacity of 129, 73, 36 and 15 C g –1 was valued using the Eq. 2 at a constant rate of 2, 5, 10 and 20 A g –1 respectively (Fig. 5 c). Furthermore, the specific energy and power were valued using equation given in the supporting section S4. The specific energy of 25, 14, 7 and 3 W h kg –1 are found to be delivered at a rate of 815, 1758, 2390 and 6389 W kg –1 respectively and it is displayed in the form of Ragone plot (Fig. 5 d). The impedance associated with the charge storage process was quantified from the X intercept and diameter of the semi-circle and it is of 7.6 and 7.4 Ω respectively (Fig. 5 e). The lifespan of the full cell was assessed for 2000 continuous charge discharge cycles and it found to be retained 85.7% of initial capacity (Fig. 5 f). 4 Conclusion The pristine and graphitic carbide added cobalt vanadium oxide nanostructures were prepared using rapid method of microwave irradiation method. The crystal structure analysis was made using XRD, resulting that the prepared materials are in the nature of poor crystalline. The valance states of the elements present in the prepared materials were studied using XPS technique. SEM analysis reveals the formation of spherical shaped cobalt vanadium oxides. Three electrode electrochemical cell was employed to investigate the charge storage performance of the prepared electrodes. All the electrodes are stored energy through the Faradaic behaviour. The incorporation of graphitic carbide nanostructures has increased the charge storage capacity of the cobalt vanadium oxide electrodes. The optimal concentration of graphitic carbide in cobalt vanadium oxide electrode is observed to be 5 wt.% by estimating the maximum specific capacity of 380 C g –1 at a specific current of 2 A g –1 . The asymmetric supercapacitor cell is designed and operated at a voltage of 1.4 V, exhibiting the pseudocapacitive energy storage process. The charged cell could release a maximum specific energy of 25 W h kg –1 at a rate of 815 W kg –1 . Furthermore, the fabricated device could retain 85.7% of capacity even after 2000 continuous charge discharge cycles. The morphological and electrochemical studies detail that the cobalt vanadium oxide incorporated with the 5 wt.% of graphitic carbon nitride is a suitable material for the construction of supercapacitors. Declarations Funding Details No fund is availed from any funding agencies. Acknowledgement The authors did not avail any funding from external agencies. Conflict of interest The authors declare no conflict of interest. Data Availability All data supporting the findings of this study are available within the manuscript and supporting information (Tables). Authors Contribution Statement Dr. S. Shanmugapriya (Correspondence and First Author)- 1. Original paper writing, 2. Conceptualization Dr. J. Johnson William (Second Author) – 1. Resources, 2. Methodology, 3. Experimental Procedure, 4. Review and Editing Dr. B. Saravanakumar (Third Author) – 1.Formal Analysis and 2.Supervision Dr. K. Somasundaram (Fourth Author) – 1.Resources and 2.Graphical interpretation References S. Sharma, P. 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Muralidharan, Nickel bismuth oxide as negative electrode for battery-type asymmetric supercapacitor, Chem. Eng. J. 422 (2021) 130058. https://doi.org/10.1016/j.cej.2021.130058. Additional Declarations No competing interests reported. Supplementary Files Supplementaryfile.docx Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Revision requested 31 Aug, 2025 Reviews received at journal 24 Aug, 2025 Reviews received at journal 14 Aug, 2025 Reviewers agreed at journal 09 Aug, 2025 Reviewers agreed at journal 09 Aug, 2025 Reviewers agreed at journal 09 Aug, 2025 Reviewers invited by journal 09 Aug, 2025 Editor assigned by journal 07 Aug, 2025 Submission checks completed at journal 07 Aug, 2025 First submitted to journal 06 Aug, 2025 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. 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-7307372","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":498218016,"identity":"2a791339-d172-4c7c-849a-dfdb441c9b1c","order_by":0,"name":"S. Shanmugapriya","email":"data:image/png;base64,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","orcid":"","institution":"NGM College of Arts and Science","correspondingAuthor":true,"prefix":"","firstName":"S.","middleName":"","lastName":"Shanmugapriya","suffix":""},{"id":498218017,"identity":"c0b58571-d48b-449e-91fb-699b7165556e","order_by":1,"name":"J. Johnson William","email":"","orcid":"","institution":"Dr. Mahalingam College of Engineering and Technology","correspondingAuthor":false,"prefix":"","firstName":"J.","middleName":"Johnson","lastName":"William","suffix":""},{"id":498218018,"identity":"9800e86e-550f-4fa7-a484-c5516ded6c9d","order_by":2,"name":"B. Saravanakumar","email":"","orcid":"","institution":"Dr. Mahalingam College of Engineering and Technology","correspondingAuthor":false,"prefix":"","firstName":"B.","middleName":"","lastName":"Saravanakumar","suffix":""},{"id":498218019,"identity":"fac8aa83-f1f3-43a4-8dc1-760406175079","order_by":3,"name":"K. Somasundaram","email":"","orcid":"","institution":"NGM College of Arts and Science","correspondingAuthor":false,"prefix":"","firstName":"K.","middleName":"","lastName":"Somasundaram","suffix":""}],"badges":[],"createdAt":"2025-08-06 08:23:11","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7307372/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7307372/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":89068666,"identity":"1faebfcc-ba7b-4e0a-9404-cd436d07d88c","added_by":"auto","created_at":"2025-08-14 10:48:20","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":343940,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eXRD analysis: X ray diffractograms of the prepared samples.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"fig1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7307372/v1/de158d5b6bb5dfda36cdd040.jpg"},{"id":89068656,"identity":"3922b375-da84-4a53-9592-3ddd6d88e638","added_by":"auto","created_at":"2025-08-14 10:48:15","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":911949,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eXPS analysis: (a) survey spectrum, wide angle spectrum of (b) V, \u0026nbsp;(c) Co, (d) O, (d) C and (e) N element of CV5GC.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"fig2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7307372/v1/71deb94e814d50602fc4570d.jpg"},{"id":89068667,"identity":"512cfc68-81a5-4873-a36b-c050e2544540","added_by":"auto","created_at":"2025-08-14 10:48:22","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":1209204,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eMorphology analysis: FESEM images of (a) CV, (b) CV2.5GC, (c) CV5GC and (d) CV7.5GC.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"fig3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7307372/v1/42db68636b92e207bc44a947.jpg"},{"id":89068660,"identity":"4903ae82-b99d-447b-a0ac-9ab76dd37957","added_by":"auto","created_at":"2025-08-14 10:48:16","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":1076028,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eElectrochemical characteristics of prepared materials: (a) CV curves recorded at 5 mV s\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e–1\u003c/strong\u003e\u003c/sup\u003e\u003cstrong\u003e, (b) CV curves of CV5GC, (c) GCD, (d) C\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003eS\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e \u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eversus\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e I\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003eD\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e, (e) Nyquist plot and (f) lifespan analysis.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"fig4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7307372/v1/b9d621b70acda31b0b2a3113.jpg"},{"id":89068804,"identity":"30e2321f-742e-4297-b6fc-1f7a24d42b14","added_by":"auto","created_at":"2025-08-14 10:48:41","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":820847,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eAssessment of ASCs energy storage characteristics: (a) CV, (b) GCD, (c) C\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003eS\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e \u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eversus\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e I\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003eD\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e, (d) Ragone plot, (e) Nyquist plot and (f) lifespan analysis.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"fig5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7307372/v1/4f2fa4c3db0f357e740a3564.jpg"},{"id":89067995,"identity":"0083c04f-7079-417e-ac62-67c96860a770","added_by":"auto","created_at":"2025-08-14 10:45:44","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":782802,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7307372/v1/a84f14fb-c3d9-4e06-88c9-09007ea860fc.pdf"},{"id":89068649,"identity":"5b1c1cbe-98a2-4666-a944-45a649983682","added_by":"auto","created_at":"2025-08-14 10:48:11","extension":"docx","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":1460756,"visible":true,"origin":"","legend":"","description":"","filename":"Supplementaryfile.docx","url":"https://assets-eu.researchsquare.com/files/rs-7307372/v1/78a50b1632038a9c61a7ad2f.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Microwave synthesis of cobalt vanadium oxide nanospheres: Boosting charge storage capacity with the addition of graphitic carbon nitride nanostructures","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eGlobal demand for energy storage devices is intensifying in every year. Energy storage devices like batteries and supercapacitors serve as a pivotal platform for the trending development of EV vehicles and portable electronic devices. Its power density and energy density mitigate the power variations, elevates the system flexibility and enhances the storage capacity. Currently, researches were marching towards supercapacitors due to its large efficiency. Some other attractive features of supercapacitors like high capacitance value, high power density, operation over wider range of temperature and high durability were also gained attention among other energy storage devices [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. The role of supercapacitors in automobile and transport systems, defence and military, computers and backup chips, medical, and industrial sectors has been reviewed by Muzaffar et al [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. Electric double layer capacitors, pseudocapacitors and hybrid supercapacitor are the classifications of supercapacitors based on their storage capacity. The charge is electrostatically stored by adsorption of ions at the surface of the electrode in EDLC whereas in pseudocapacitors, the charges are stored electrochemically by rapid redox reactions [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. The energy storage capacity of pseudocapacitors is far greater than the electric double layer capacitors due to the nature of electrode materials used in their assembly.\u003c/p\u003e\u003cp\u003eTransition metal-based compounds are widely used as active materials for supercapacitors. Among, cobalt vanadium oxide is a promising material for various electrochemical applications due to its unique redox characteristics, structural stability, and versatile oxidation states. It exhibits intriguing electrochemical properties that make it valuable in applications such as lithium-ion batteries, supercapacitors, and electrochemical sensors. cobalt vanadium oxide demonstrates a robust ability to undergo reversible redox reactions involving both cobalt and vanadium ions, which contribute significantly to its high specific capacity and excellent energy storage potential. These redox reactions involve the transformation between multiple oxidation states, including Co\u003csup\u003e2+/3+\u003c/sup\u003e and V\u003csup\u003e3+/5+\u003c/sup\u003e, which enhances its electrochemical activity. The presence of both cobalt and vanadium also contributes to a synergistic effect that improves the overall electronic conductivity and stability of the oxide, enhancing charge storage and electron transfer processes. Furthermore, its high theoretical capacity, attributed to multiple electron transfer processes, enables cobalt vanadium oxide to maintain high charge and discharge rates, which is essential for high-performance energy storage applications. Besides, studies indicate that cobalt vanadium oxide anodes suffer to sustain performance during prolonged cycling. To address this, researchers have explored nanostructured cobalt vanadium oxide or its composites with carbonaceous materials to improve cycling stability and electrical conductivity.\u003c/p\u003e\u003cp\u003eCurrently, graphitic carbon nitride nanostructures are emerged as an efficient material to enhance the electrochemical performance of the metal oxides when the graphitic carbon nitride nanostructures are added in the preparation of composites [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e][\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e][\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e][\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e][\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e][\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e][\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. Moreover, graphitic carbon nitride nanostructures is a desirable material due to its large nitrogen content, large surface area, lower impedance, tuneable structure and higher potential for electrode applications [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. The semiconductor nature of graphitic carbon nitride exhibits excellent catalytic activity for various reactions like oxygen reduction [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e][\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e], hydrogen production [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e][\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e], photo-catalytic [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e], electrochemical sensing [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e] and electrochemical energy storage [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. The polymer matrix of graphitic carbon nitride builds it to be economical and non-toxic electrode materials for wider applications. The facile synthesis by thermal polymerization using nitrogen rich precursors like cyanamide, melamine, dicyandiamide, thiourea, ammonium thiocyanate, and urea is one of the main attractive features of graphitic carbon nitride. Owing to the nature of these efficient features, GCN nanostructures are incorporated into the metal oxide nanostructures to elevate the charge storage performance. It is worth to mention that the GCN grafted transition metal oxides material has larger surface area and more active sites at the electrode-electrolyte interface, which facilitates the ionic diffusion, thus enhancing the faradaic reaction and the supercapacitor performance [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eIn the present work, we have prepared the binary transition metal oxide (Cobalt vanadium oxide) composites grafted with graphitic carbon nitride through simple and effective microwave oven method. XRD analysis was carried out to study the structural properties. SEM analysis was made to examine the morphological nature of prepared samples. The chemical composition of sample surface was revealed by XPS analysis. The electrochemical properties of the samples were analysed using three electrode system.\u003c/p\u003e"},{"header":"2. Experimental","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003e2.1. Preparation of Graphitic carbon nitride integrated Cobalt Vanadium oxide nanostructures:\u003c/h2\u003e\u003cp\u003eGraphitic carbon nitride added cobalt vanadium oxide nanomaterials were prepared through microwave oven technique. In 180 ml of double distilled water, 10 wt.% of CTAB was dissolved and stirred continuously. 0.5238 g of cobalt (II) nitrate hexahydrate and 0.4211 g of ammonium metavanadate were dissolved in the solution containing 10 Wt.% of CTAB. Further, different weight per cent of gaphitic carbon nitride (2.5, 5 and 7.5 wt.%) was added to the above blended solution and continuously stirred to obtain a homogenous solution. Besides, 1 M NaOH was prepared and gradually added to the resultant solution to adjust the pH to 10. The final resultant solution was treated at power of 360 W, microwave energy for 10 minutes. Finally, the precipitate was washed with distilled water and dried at 60\u0026deg;C for 12 hours. The as-formed particles were calcined for one hour at 300\u0026deg;C and named as CV2.5GC, CV5GC and CV7.5GC for the cobalt vanadium oxide comprised of 2.5, 5 and 7.5 wt.% of graphitic carbon nitride. Similarly, the pristine cobalt vanadium oxide nanostructures were prepared using same procedure without the addition of graphitic carbon nitride and named as CV.\u003c/p\u003e\u003c/div\u003e\n\u003ch3\u003e\u003c Fig. . XRD analysis: X ray diffractograms of the prepared samples \u003e\u003c/h3\u003e\n\u003cp\u003e\u003c/p\u003e\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\u003ch2\u003e2.2 Characterization techniques\u003c/h2\u003e\u003cp\u003eThe detailed specifications of the instruments used to characterize the structural, morphological and electrochemical analysis are discussed in the supporting information S1 and S2.\u003c/p\u003e\u003c/div\u003e"},{"header":"3. Result and discussions","content":"\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e\u003ch2\u003e3.1 Structural analysis\u003c/h2\u003e\u003cp\u003eThe structural characterization of prepared nanomaterials was detected using X-Ray Diffractometer spectroscopy (XRD). Figure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e demonstrates the diffractograms of the prepared materials, indicating the poor crystalline nature. Incorporation of graphitic carbide does not make significant impact on the XRD profile of cobalt vanadium oxides and all the samples remain in the amorphous nature. Besides, XPS analysis was made to examine the valance states of the prepared materials and their results are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. The survey scan of the composite in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea indicates the presence of Co 2p, V 2p, O 1s and C 1s. The wide-angle spectrum of V 2p element is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb, exhibiting multiple peaks at 517.15, 518.29, 524.19 and 525.27 eV and it corresponds to the V\u003csup\u003e5+\u003c/sup\u003e of V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e, V\u003csup\u003e4+\u003c/sup\u003e of VO\u003csub\u003e2\u003c/sub\u003e and their corresponding satellites respectively, indicating that the vanadium element is existed in its oxidation states of +\u0026thinsp;4 and +\u0026thinsp;5. Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec shows the highly resolved XPS spectrum of Co 2p element. The obtained spectrum was fitted with the various centered at 780.88, 782.26, 787.29, 791.33, 797.35 and 803.47 eV, indicating the presence of Co\u003csup\u003e2+\u003c/sup\u003e of 2p\u003csub\u003e3/2\u003c/sub\u003e, Co\u003csup\u003e3+\u003c/sup\u003e of 2p\u003csub\u003e3/2\u003c/sub\u003e, satellite of Co\u003csup\u003e3+\u003c/sup\u003e, satellite of Co\u003csup\u003e2+\u003c/sup\u003e, satellite of Co\u003csup\u003e3+\u003c/sup\u003e, Co\u003csup\u003e2+\u003c/sup\u003e of 2p\u003csub\u003e1/2\u003c/sub\u003e and satellite of Co\u003csup\u003e3+\u003c/sup\u003e respectively [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e][\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e][\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. The chemical environment of oxygen element is assessed using its deconvoluted profile (Figure d). The peaks found at 530.3 and 531 eV indicate the lattice oxygen or in a metal-oxygen bond [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e][\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. The presence of oxygen vacancies is identified from the XPS line centered at 532 eV. Moreover, the peak positioned at 533 eV signifies the existence of surface adsorbed species. Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ee demonstrates the deconvoluted XPS spectrum of C 1s element. The peaks positioned at 284.92 and 285.66 eV represents the sp\u003csup\u003e2\u003c/sup\u003e hybridized graphitic carbon (C-C/C\u0026thinsp;=\u0026thinsp;C) and carbon bonded to nitrogen in g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e, respectively. The presence of oxygenated and amide type bonding in g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e is observed from the peaks, located at 286.58 and 287.45 eV respectively [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. The XPS line, centered at 288.46 and 289.54 eV reveals formation of N-C\u0026thinsp;=\u0026thinsp;N/C\u0026thinsp;=\u0026thinsp;O bond and carbonated (O\u0026thinsp;=\u0026thinsp;C-O) species in the prepared composites [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. Besides, the wide-angle spectrum of N 1s element is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ef, displaying XPS line at a binding energy of 397.23, 400.15 and 403.68 eV and it corresponds to the sp2 hybridized nitrogen (C\u0026thinsp;=\u0026thinsp;N-C), sp3 hybridized nitrogen (C-N-C) and oxidized nitrogen species respectively.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003cb\u003e\u0026lt;\u003c/b\u003e Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. \u003cb\u003eXPS analysis: (a) survey spectrum, wide angle spectrum of (b) V, (c) Co, (d) O, (d) C and (e) N element of CV5GC. \u0026gt;\u003c/b\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\u003ch2\u003e3.2. Morphological analysis\u003c/h2\u003e\u003cp\u003e\u003cb\u003e\u0026lt;\u003c/b\u003eFigure \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. \u003cb\u003eMorphology analysis: FESEM images of (a) CV, (b) CV2.5GC, (c) CV5GC and (d) CV7.5GC \u0026gt;\u003c/b\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe surface morphology of prepared materials was analyzed using field emission scanning electron microscopy (FESEM). FESEM images of pristine and graphitic carbon nitride incorporated cobalt vanadium oxide nanostructures are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. All the samples display the spherical shaped particles with the size in the range of nanometer. Moreover, the particles are formed in a uniform manner. The addition of graphitic carbon nitride has found to be influenced in the cobalt vanadium oxide particle size and it could be clearly seen from the Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb-c. The size of the particles is reduced when the concentration of graphitic carbon nitride is increased to 5wt.% (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec) and size is increased for further increasing the concentration of graphitic carbon nitride to 7.5 wt.% (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed). Thus, cobalt vanadium oxide nanospheres prepared under the medium of 5 wt.% graphitic carbon nitrides are uniformly distributed with the size smaller than the other samples. Hence, 5 wt.% graphitic carbon nitrides are suitable concentration for the preparation of uniform sized cobalt vanadium oxide particles.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e\u003ch2\u003e3.3 Analysis of supercapacitive performance\u003c/h2\u003e\u003cp\u003eThe supercapacitor performance of graphitic carbon incorporated cobalt vanadium oxide electrodes was studied using three-electrode electrochemical cell in 2 M aqueous KOH solution. The electrochemical performance was analysed using time domain and frequency domain. The cyclic voltammetry and galvanostatic charge-discharge measurement were based on time domain whereas impedance analysis relies on frequency domain. The CV measurements were carried out within the potential window between \u0026minus;\u0026thinsp;0.5 to 0.25 V at various scan rates, ranged from 5 to 100 mV s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and their results are displayed in supporting Figure \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e, 4 a and b. The CV curves of all the samples portray non-rectangular shapes displaying strong redox peaks. The swift of anodic and cathodic peaks towards the higher and lower potential, respectively, is observed while increasing the scan rates, which is attributed to Faradaic behaviour [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. During forward scan, the electrode is oxidised with the removal of electron (Co\u003csup\u003e0\u003c/sup\u003e - Co\u003csup\u003e2+\u003c/sup\u003e) and it is represented by the anodic peak at higher potential. Similarly, reverse scan, the electron is added (Co\u003csup\u003e2+\u003c/sup\u003e- Co\u003csup\u003e0\u003c/sup\u003e) to the electrode materials, indicating by the cathodic peak at lower potential. The oxidation peak during charging process portrays the energy storing capacity while during discharge process, the reduction peak reveals the energy releasing process. The area under the CV curves for graphitic carbon grafted cobalt vanadium oxide electrode was found to be higher than the area encircled by pristine cobalt vanadium oxide. This observation indicates that the inclusion of graphitic carbon enhances the electrochemical performance of cobalt vanadium oxides. The CV curve depicts the appreciable reversibility and high-rate capability at the interface of electrode and electrolyte. The specific capacities are calculated using an Eq.\u0026nbsp;1 and it is given in a supporting information S4. The estimated specific capacities of all the samples is given in the supporting table S4. The specific capacity of 224, 225, 301 and 235 C g\u003csup\u003e\u0026ndash;1\u003c/sup\u003e is estimated at a scan rate of 5 mV s\u003csup\u003e\u0026ndash;1\u003c/sup\u003e for the electrodes of CV, CV2.5GC, CV5GC and CV7.5GC respectively. The electrodes of CV5GC exhibit superior specific capacity when compared to other electrodes. This may be due to the enhanced EDLC behaviour with the inclusion of graphitic carbon leading to the increased current density. Moreover, the charge storage capacity was found to be degrading when the scan rate reaches infinity and it may be due to the lesser diffusion time of electrolyte ions [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e].\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u0026lt;Figure \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. \u003cb\u003eElectrochemical characteristics of prepared materials: (a) CV curves recorded at 5 mV s\u003c/b\u003e\u003csup\u003e\u003cb\u003e\u0026ndash;1\u003c/b\u003e\u003c/sup\u003e, \u003cb\u003e(b) CV curves of CV5GC, (c) GCD, (d) C\u003c/b\u003e\u003csub\u003e\u003cb\u003eS\u003c/b\u003e\u003c/sub\u003e \u003cb\u003eversus\u003c/b\u003e \u003cb\u003eI\u003c/b\u003e\u003csub\u003e\u003cb\u003eD\u003c/b\u003e\u003c/sub\u003e, \u003cb\u003e(e) Nyquist plot and (f) lifespan analysis\u0026gt;\u003c/b\u003e\u003c/p\u003e\u003cp\u003eTo further investigate the electrochemical properties of sample, galvanostatic charge-discharge analysis was conducted within the potential window of -0.5 to 0.25 V. The study was carried out at different specific currents and their results are displayed in the supporting Figure S2 and 4c, demonstrating the non-linear behaviour for all electrodes. This nature portrays that the prepared materials exhibit excellent faradic behaviour for storing appreciable charges. The GCD studies also reveal that CV5GC electrode encircles larger discharge area, illustrating the enhanced supercapacitor performance than the other electrodes. The specific capacity (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ed) of all the electrodes was calculated using the Eq.\u0026nbsp;2 and it is given in supporting information S4. The specific capacities of all electrodes are estimated and it is given in the supporting table S6. The specific capacity of CV, CV2.5GC, CV5GC and CV7.5GC electrodes is estimated and it found to be 168, 179, 380 and 236 C g\u003csup\u003e\u0026ndash;1\u003c/sup\u003e respectively. The addition of graphitic carbide has significantly improved the charge storage performance, resulting in an enhancement of specific capacity. A maximum of 380 C g\u003csup\u003e\u0026ndash;1\u003c/sup\u003e is estimated for cobalt vanadium oxide electrode consisted of 5 wt.% of graphitic carbide nanostructures. Moreover, the specific capacity is found to be decreased on increasing the current density and it is due to less time find for electrolyte ions to diffuse into the electrode materials [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eThe electrochemical impedance spectroscopy was implemented to study the charge transport characteristics of the prepared electrodes. A frequency range of 0.01 Hz to 100 kHz is used to analyse the electrochemical performance of the electrodes. The obtained impedance spectra were fitted to the modified Randle\u0026rsquo;s circuit (inset of Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ee). Generally, the Nyquist plot consists of a semicircle in the high frequency region and inclined spike in the low frequency region. The presence of semicircle signifies the electrochemical reactions prevailing at the electrode/electrolyte interface. The inclined spike in the low frequency indicates the diffusive nature of OH\u003csup\u003e\u0026minus;\u003c/sup\u003e ions into the matrix of electrodes. The ohmic resistance between the solution and electrode is obtained from the point of intersection between the real axis and the curve and the charge transfer resistance is estimated from the radius of semicircle arc. The inclined spike in the low frequency region is related to the diffusion impedance (Warburg impedance, Z\u003csub\u003eW\u003c/sub\u003e) [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. The solution and charge transfer resistance is obtained for all the samples from the X-intercept and diameter of the semi-circle. The solution resistance of 3.54, 1.03, 0.968 and 1.549 Ω and charge transfer resistance of 3.17, 0.56, 0.37 and 0.78 Ω is obtained for the electrodes of CV, CV2.5GC, CV5GC and CV7.5GC, respectively.\u003c/p\u003e\u003cp\u003eThe stability of CV and CV5GC electrodes was examined for 5000 continuous cycles at a current density of 15 A g\u003csup\u003e\u0026ndash;1\u003c/sup\u003e. The capacity retention is evaluated for each 100 cycles (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ef). The retention of 74 and 92% is found to be retained for the electrodes of pristine and graphitic carbide added cobalt vanadium oxide nanostructures, respectively even after 5000 GCD cycles. The increase in retention is mainly due to the opening of channels on continuous cycling which enhances the electroactive sites in the composites. The diffusion of electrolyte ions within the material is increased as the huge electroactive sites were been triggered leading to the intensified electrochemical performance. Also, during the continuous cycling, wetting of the particles provides the huge new channels which trails the better access of sites for storing charges.\u003c/p\u003e\u003cp\u003e\u003cb\u003e\u0026lt;\u003c/b\u003eFigure \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e. \u003cb\u003eAssessment of ASCs energy storage characteristics: (a) CV, (b) GCD, (c) C\u003c/b\u003e\u003csub\u003e\u003cb\u003eS\u003c/b\u003e\u003c/sub\u003e \u003cb\u003eversus\u003c/b\u003e \u003cb\u003eI\u003c/b\u003e\u003csub\u003e\u003cb\u003eD\u003c/b\u003e\u003c/sub\u003e, \u003cb\u003e(d) Ragone plot, (e) Nyquist plot and (f) lifespan analysis\u003c/b\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e\u003ch2\u003e3.4 Assessment of two electrode system\u003c/h2\u003e\u003cp\u003eBesides, full cell is assembled by employing the cobalt vanadium oxide comprised of 5wt.% of graphitic carbon nitride as the counter electrode to the activated carbon. The measurement was done at an operating voltage of 1.4 V. Figure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e shows the results of electrochemical performance of fabricated device, exhibiting the pseudocapacitive nature (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea\u0026amp;b) of energy storage process. The specific capacity of 129, 73, 36 and 15 C g\u003csup\u003e\u0026ndash;1\u003c/sup\u003e was valued using the Eq.\u0026nbsp;2 at a constant rate of 2, 5, 10 and 20 A g\u003csup\u003e\u0026ndash;1\u003c/sup\u003e respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ec). Furthermore, the specific energy and power were valued using equation given in the supporting section S4. The specific energy of 25, 14, 7 and 3 W h kg\u003csup\u003e\u0026ndash;1\u003c/sup\u003e are found to be delivered at a rate of 815, 1758, 2390 and 6389 W kg\u003csup\u003e\u0026ndash;1\u003c/sup\u003e respectively and it is displayed in the form of Ragone plot (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ed). The impedance associated with the charge storage process was quantified from the X intercept and diameter of the semi-circle and it is of 7.6 and 7.4 Ω respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ee). The lifespan of the full cell was assessed for 2000 continuous charge discharge cycles and it found to be retained 85.7% of initial capacity (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ef).\u003c/p\u003e\u003c/div\u003e"},{"header":"4 Conclusion","content":"\u003cp\u003eThe pristine and graphitic carbide added cobalt vanadium oxide nanostructures were prepared using rapid method of microwave irradiation method. The crystal structure analysis was made using XRD, resulting that the prepared materials are in the nature of poor crystalline. The valance states of the elements present in the prepared materials were studied using XPS technique. SEM analysis reveals the formation of spherical shaped cobalt vanadium oxides. Three electrode electrochemical cell was employed to investigate the charge storage performance of the prepared electrodes. All the electrodes are stored energy through the Faradaic behaviour. The incorporation of graphitic carbide nanostructures has increased the charge storage capacity of the cobalt vanadium oxide electrodes. The optimal concentration of graphitic carbide in cobalt vanadium oxide electrode is observed to be 5 wt.% by estimating the maximum specific capacity of 380 C g\u003csup\u003e\u0026ndash;1\u003c/sup\u003e at a specific current of 2 A g\u003csup\u003e\u0026ndash;1\u003c/sup\u003e. The asymmetric supercapacitor cell is designed and operated at a voltage of 1.4 V, exhibiting the pseudocapacitive energy storage process. The charged cell could release a maximum specific energy of 25 W h kg\u003csup\u003e\u0026ndash;1\u003c/sup\u003e at a rate of 815 W kg\u003csup\u003e\u0026ndash;1\u003c/sup\u003e. Furthermore, the fabricated device could retain 85.7% of capacity even after 2000 continuous charge discharge cycles. The morphological and electrochemical studies detail that the cobalt vanadium oxide incorporated with the 5 wt.% of graphitic carbon nitride is a suitable material for the construction of supercapacitors.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eFunding Details\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNo fund is availed from any funding agencies.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors did not avail any funding from external agencies.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no conflict of interest.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData Availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll data supporting the findings of this study are available within the manuscript and supporting information (Tables).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors Contribution Statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDr. S. Shanmugapriya\u003c/strong\u003e (Correspondence and First Author)- 1. Original paper writing, 2. Conceptualization\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDr. J. Johnson William\u0026nbsp;\u003c/strong\u003e(Second Author) \u0026ndash; 1. Resources, 2. Methodology, 3. Experimental Procedure, \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; 4. Review and Editing\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDr. B. Saravanakumar\u003c/strong\u003e (Third Author) \u0026ndash; 1.Formal Analysis and 2.Supervision\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDr. K. Somasundaram\u003c/strong\u003e (Fourth Author) \u0026ndash; 1.Resources and 2.Graphical interpretation\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eS. Sharma, P. Chand, Supercapacitor and electrochemical techniques : A brief review, Results Chem. 5 (2023) 100885. https://doi.org/10.1016/j.rechem.2023.100885.\u003c/li\u003e\n\u003cli\u003eA. Muzaffar, M.B. Ahamed, K. 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J. 422 (2021) 130058. https://doi.org/10.1016/j.cej.2021.130058.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"ionics","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":" Learn more about [Ionics](https://www.springer.com/journal/11581) ","snPcode":"11581","submissionUrl":"https://mc.manuscriptcentral.com/ionics","title":"Ionics","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"cobalt vanadium oxide, graphitic carbon nitride, nanospheres, pseudocapacitive-type, asymmetric cell","lastPublishedDoi":"10.21203/rs.3.rs-7307372/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7307372/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe development of high-performance electrode materials is critical for enhancing the energy storage capabilities of supercapacitors. In this study, cobalt vanadium oxide and its graphitic carbon nitride composites were synthesized and investigated as an electrode material for supercapacitors. The green chemistry, microwave method was employed for the preparation of nanocomposites. The XRD analysis results indicate that the cobalt vanadium oxides are in a poor crystalline nature. The formation of nanosphere shaped morphology is found in the FESEM analysis. The addition of graphitic carbon nitride benefits in the formation of uniformly distributed cobalt vanadium oxide nanospheres. The valance states of the elements presented in the prepared composite were examined using XPS technique. Half-cell mode was employed to assess the charge storage process of the prepared materials. The electrodes of the prepared materials store energy through the pseudocapacitive nature. The electrodes of cobalt vanadium oxide, consisted of 5 wt.% graphitic carbon nitride yields maximum capacity of 380 C g\u003csup\u003e\u0026ndash;1\u003c/sup\u003e and it is 226% higher than the pristine cobalt vanadium oxide electrodes. Besides, full-cell was devised using activated carbon as the counter electrode. The assembled device could yield maximum specific energy of 25 W h kg\u003csup\u003e\u0026ndash;1\u003c/sup\u003e at a rate of 815 W kg\u003csup\u003e\u0026ndash;1\u003c/sup\u003e. Moreover, 12% of energy was found to be retained when rate of delivery is increased to 7.8 fold. All the studies represent that the graphitic carbon nitride added cobalt vanadium oxide nanospheres are suitable materials for the construction of supercapacitors.\u003c/p\u003e","manuscriptTitle":"Microwave synthesis of cobalt vanadium oxide nanospheres: Boosting charge storage capacity with the addition of graphitic carbon nitride nanostructures","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-08-14 10:40:27","doi":"10.21203/rs.3.rs-7307372/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-08-31T11:02:20+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-08-24T15:36:11+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-08-14T15:36:51+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"182355594310904536396958280333743505330","date":"2025-08-09T14:02:04+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"118099678728435872569223329785672688138","date":"2025-08-09T11:14:48+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"160341005097221332371181847385179255457","date":"2025-08-09T09:38:46+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-08-09T08:41:04+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-08-07T22:32:11+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-08-07T22:30:22+00:00","index":"","fulltext":""},{"type":"submitted","content":"Ionics","date":"2025-08-06T08:08:54+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"ionics","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":" Learn more about [Ionics](https://www.springer.com/journal/11581) ","snPcode":"11581","submissionUrl":"https://mc.manuscriptcentral.com/ionics","title":"Ionics","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"f1a2d3e7-fe11-45aa-93f8-c71c7491a7cc","owner":[],"postedDate":"August 14th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2025-09-29T21:53:24+00:00","versionOfRecord":[],"versionCreatedAt":"2025-08-14 10:40:27","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7307372","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7307372","identity":"rs-7307372","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}