{"paper_id":"0fc194f5-9124-4e6d-b540-bb0fa2fb3034","body_text":"Effects of Electrolyte Substitution on the Electrochemical Performance of Spinel Nickel Manganese Oxide Nanostructures for Supercapacitor Applications | 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 Effects of Electrolyte Substitution on the Electrochemical Performance of Spinel Nickel Manganese Oxide Nanostructures for Supercapacitor Applications Pragati N. Thonge, Suprimkumar D. Dhas, Tushar T. Bhosale, Falah Awwad, and 6 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9306053/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 A facile hydrothermal method was employed to synthesize NiMn 2 O 4 (NMO) nanostructures (NSs) for application as electrode materials in high-performance supercapacitors. The synthesised NMO-NSs were characterised by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS). Electrochemical performance was evaluated using cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS) in 4 M KOH and 4 M LiOH aqueous electrolytes. The NMO@NF electrode exhibited a high specific capacity of 511 C g − 1 at a scan rate of 5 mV s − 1 in 4 M LiOH electrolyte. Furthermore, the electrode demonstrated excellent cyclic stability with less than 1% degradation after 2000 cycles. These results highlight the significant influence of electrolyte selection on the electrochemical performance of NiMn 2 O 4 -based supercapacitors. Electrolyte substitution NiMn2O4 Hydrothermal synthesis Supercapacitor Energy storage Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 1. Introductions The supercapacitors serve as a bridge between batteries and conventional capacitors due to their high specific power density, rapid charge-discharge performance, and excellent cycle life. The energy storage mechanism of the electrochemical capacitor depends on electric double-layer capacitors (EDLCs) and pseudocapacitors. Enhancing the interaction between the electrode and the electrolyte is necessary to improve the supercapacitive performance [ 1 – 4 ]. The most important factors in producing high-performance supercapacitors are the quantity of active sites and the nature of the electrode nanomaterials, including increasing surface area to provide more active sites. To improve electrochemical performance, a few researchers have concentrated on increasing surface area by synthesizing porous nanomaterials [ 5 – 6 ]. Despite their low conductivity, spinel metal oxides (AB 2 O 4 ) have been employed as electrode active materials due to the different oxidation states of the elements that can be substituted on A/B cation octahedral and tetrahedral sites, allowing for flexible chemical properties and various redox-active sites. Among different spinel metal oxides, NiMn 2 O 4 (NMO) has been only sparingly explored for supercapacitor applications [ 7 – 8 ]. So far, NM-NSs have been synthesized in different forms by a variety of chemical routes such as sol-gel [ 9 ], co-precipitation method [ 10 ], electrospinning [ 11 ], and hydrothermal route, etc. [ 12 ]. The method used to synthesise NSs greatly influences their physicochemical properties. Therefore, economically viable, environmentally safe, fast-moving, and energy-efficient synthesis routes are essential for the mass production of NSs [ 13 ]. The hydrothermal method is considered a versatile, cost-effective wet-chemical method. In this synthesis technique, by varying preparative parameters such as temperature, pH, and precursor molarity, the morphology and particle size of the materials can be controlled [ 14 ]. A streamlined active-material manufacturing process must be developed to produce supercapacitors on a large scale and at a reasonable cost. Here, we describe a hydrothermal method to make NMO-NSs and extensively examine the impact of the electrolytes (4 M KOH and 4 M LiOH) on their electrochemical features. The proposed supercapacitor electrodes in a cell containing 4 M LiOH begin to exhibit intriguing characteristics, including improved electrochemical performance due to the smaller ionic radius and slower nickel dissolution into the LiOH electrolyte. These might enable the fabrication of high-performance supercapacitors on a large scale. The current work focuses on the redox additive-assisted alkaline electrolyte as a new approach to enhance capacitance for supercapacitor applications, in light of current research trends on redox-active additives in aqueous electrolytes for supercapacitor applications. Here, the emphasis of NMO@NF is on using LiOH in the alkaline solution to increase the specific capacitance of the redox-active electrode in a safe and environmentally acceptable manner. NMO@NF displayed a typical redox potential between 0 and 0.7 V, which was enhanced by the particular reaction in the presence of LiOH electrolyte. A simple hydrothermal method was used to produce an easy-to-make, affordable cation-intercalated NMO@NF electrode. Ion movement was enhanced, and further support was provided for the intercalation/de-intercalation of the ions during the oxidation/reduction processes in LiOH over KOH by the spinel NMO. In a KOH and LiOH electrolyte, the as-prepared electrode with K + and Li + intercalated was measured to have a specific capacity. The NMO@NF electrode demonstrated a specific capacity of 511 Cg − 1 at a scan rate of 5 mV s − 1 and maintained its high electrochemical performance even after 2000 CV cycles. After 2000 CV cycles, the NMO@NF electrode demonstrated cyclic stability retention of up to 99% and 93% in 4 M LiOH and 4 M KOH electrolytes, respectively. 2. Experimental 2.1 Materials Lithium hydroxide (LiOH), potassium hydroxide (KOH), manganese acetate (Mn(NO 3 ) 2 .xH 2 O), nickel acetate (Ni(NO 3 ) 2 .xH 2 O), methanol (CH 3 OH), Polyvinylidene fluoride (PVDF), NMP solvent, nickel foam (NF) and carbon black were purchased from Sigma Aldrich, India. All chemicals were of analytical grade and used without further purification. 2.2 Characterization techniques The X-ray diffraction (XRD) patterns of the NMO-NSs in the range of 2θ = 15 0 to 80 0 were obtained with an X-ray D2 Phaser diffractometer, Bruker Ltd. (Germany), (Cu-Kα, λ = 1.5405 Å) instrument. Field emission scanning electron microscopy (FE-SEM) and energy-dispersive X-ray (EDS) elemental analysis were obtained on a JSM-6160 Jeol Ltd. (Japan). N 2 adsorption/desorption isotherms were obtained at Quantachrome NOVA 1000e (USA) to examine Brunauer−Emmett−Teller specific surface areas of the nanomaterial, and the pore size distribution was assessed via the fitting model established by Barrett−Joyner−Halenda (BJH). The electrochemical properties of the NMO@NF electrode were assessed through a three-electrode system in 4 M KOH and 4 M LiOH electrolytes using a Potentiostat (Model-VMP3-Bio-Logic, France). 2.3 Synthesis of NMO-NSs by the hydrothermal method NiMn 2 O 4 (NMO) nanostructures were synthesized via a facile hydrothermal method. In a typical procedure, stoichiometric amounts of nickel acetate tetrahydrate (Ni(CH 3 COO) 2 ·4H₂O) and manganese acetate tetrahydrate (Mn(CH 3 COO) 2 ·4H₂O) were dissolved in a mixed solvent system of double-distilled water under constant stirring to form a homogeneous solution. The resulting solution was transferred into a stainless-steel autoclave and maintained at 120°C for 4 h. After naturally cooling to room temperature, the obtained precipitate was collected and thoroughly washed several times with double-distilled water and ethanol to remove residual impurities. The purified product was then dried at 60°C and subsequently calcined in a muffle furnace at 500°C for 4 h to obtain highly crystalline NiMn 2 O 4 nanostructures. 2.4 Preparation of NMO-NF working electrode Before electrode fabrication, nickel foam (NF) substrates (3 cm × 1 cm) were pretreated to remove surface impurities. The NF was ultrasonically cleaned in diluted hydrochloric acid (HCl) for 30 min, followed by repeated washing with ethanol and double-distilled water (DDW), and then dried under ambient conditions. The working electrodes were prepared by mixing the active material (NiMn 2 O 4 ), carbon black, and polyvinylidene difluoride (PVDF) binder in a weight ratio of 8:1:1 using N-methyl-2-pyrrolidone (NMP) as the solvent to form a homogeneous slurry. The resulting slurry was uniformly coated onto the pretreated NF substrate, which served as the current collector. The coated electrodes were then dried overnight at 60°C to ensure complete solvent removal and proper adhesion of the active material. The mass loading of the active material on the NF substrate was approximately 14 mg cm − 2 . The prepared electrodes, denoted NMO–NF, were used for subsequent electrochemical measurements. 2.5 Electrochemical analysis The electrochemical measurements, cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance (EIS), were performed in 4 M KOH and 4 M LiOH electrolytes using a three-electrode arrangement on a VMP-3-based electrochemical workstation. A platinum plate and an SCE electrode were used as counter and reference electrodes, respectively. The Cs by CV and GCD, respectively, are calculated according to the following equations [ 15 – 16 ]: C = \\(\\:\\frac{1}{\\text{M}V}{\\int\\:}_{{\\text{V}}_{\\text{i}}}^{{\\text{V}}_{\\text{f}}}\\text{I}\\:\\left(\\text{V}\\right)\\text{d}\\text{v}\\) (1) Cs = \\(\\:\\frac{\\text{I}\\varDelta\\:\\text{t}\\:}{M}\\) (2) where C (F g − 1 ) is the specific capacity, I (mA) represents the discharge current, and M (mg) is the mass of active materials, \\(\\:\\text{V}\\) (V) is the scan rate and \\(\\:\\varDelta\\:\\text{t}\\) (sec) designates discharge and total discharge time. 3. Results and discussions The XRD pattern ( Fig. 2 a ) confirms the formation of a well-crystallized spinel NiMn 2 O 4 phase, with all diffraction peaks matching the standard ICDD data (Card No. 00-001-1110), indicating phase purity without any detectable impurities. The sharp and well-defined peaks corresponding to the (220), (311), (400), (511), and (533) planes suggest high crystallinity of the synthesized material. The FE-SEM image ( Fig. 2 b ) reveals that the NMO nanostructures exhibit irregular grain-like morphology with rough surfaces, which can provide a large number of electrochemically active sites. Such surface features enhance electrolyte interaction and improve electrochemical performance. The observed structural and morphological features are expected to facilitate efficient ion transport and redox activity. The EDS analysis ( Fig. 2 c ) confirms the presence of Ni, Mn, and O, with uniform distribution throughout the sample, verifying the successful formation of stoichiometric NiMn 2 O 4 without extraneous elements. Furthermore, the homogeneous elemental distribution indicates effective mixing of metal precursors during synthesis, which is crucial for achieving uniform electrochemical activity. In addition, the absence of any impurity peaks in the XRD pattern and the consistent elemental composition from EDS analysis further validate the phase purity and compositional integrity of the material. The interconnected grain-like morphology may also contribute to improved electrical conductivity by providing continuous pathways for electron transport. Moreover, the rough and porous surface can enhance electrolyte penetration, thereby increasing the accessibility of active sites during redox reactions. Overall, the combined XRD, FE-SEM, and EDS results demonstrate the successful synthesis of phase-pure, highly crystalline, and morphologically favourable NiMn 2 O 4 nanostructures for electrochemical applications, particularly in energy storage systems. Whereas Fig. 3 (a) reveals the N 2 adsorption–desorption isotherms of the NMO-NSs. The Brunauer–Emmett–Teller (BET) specific surface area and average pore diameter (Fig. 3 (b) ) of the NMO-NSs are nearly 46.13 m 2 g − 1 and 6.75 nm, respectively, indicating that the hydrothermally synthesized NMO-NSs possess a relatively large surface area. The NMO-NSs exhibit a predominant mesoporous distribution in the pore size range of 2 to 10 nm, which is highly favourable for enhanced redox reactions and ion intercalation processes. Such mesoporous characteristics facilitate rapid diffusion of electrolyte ions and improve charge-transfer kinetics during electrochemical operation. Additionally, the increased surface area provides more active sites, thereby enhancing electrochemical performance. The CV curves of the NMO@NF electrode in 4 M LiOH and 4 M KOH electrolytes are shown in Fig. 4 (a) and 4(b) , respectively, within the potential window of 0–0.7 V (vs. SCE) at different scan rates. The CV curves clearly exhibit more pronounced redox peaks in the LiOH electrolyte than in the KOH electrolyte, indicating a battery-type behaviour of the NMO@NF electrode. The presence of distinct redox peaks arises from Faradaic reactions occurring at the electrode-electrolyte interface [ 17 ]. Furthermore, the CV curves reveal that the NMO@NF electrode in 4 M LiOH exhibits a larger enclosed area than that in 4 M KOH, suggesting superior charge storage capability. The calculated specific capacities are 312 C g − 1 and 551 C g − 1 for 4 M KOH and 4 M LiOH electrolytes, respectively, at a scan rate of 5 mV s − 1 . The enhanced performance in LiOH can be attributed to the smaller ionic radius of Li + (0.09 nm) compared to K + (0.152 nm), which facilitates faster ion diffusion. Additionally, the larger hydrated radius of K + results in lower mobility in aqueous electrolytes, thereby limiting its electrochemical performance [ 18 – 19 ]. The following equations form the basis of the oxidation-reduction reactions of NiMn 2 O 4 in the alkaline KOH and LiOH electrolytes: [ 21 – 22 ]. NiMn 2 O 4 + OH − + H 2 O ↔ NiOOH + 2MnOOH + 2e − (1) MnOOH + OH − ↔ MnO 2 + H 2 O + e − (2) Therefore, the improved electrochemical performance observed in LiOH electrolyte is mainly due to the smaller ionic size of Li + ions and reduced dissolution of nickel species, consistent with previous reports [ 20 ]. Figure 4 (c) shows the comparative CV curves of the NMO@NF electrode in both electrolytes at a scan rate of 100 mV s − 1 . The presence of one oxidation peak during the anodic scan and one reduction peak during the cathodic scan confirms that the charge storage mechanism is dominated by Faradaic processes. These redox peaks are associated with the reversible Ni 2+ /Ni 3+ and Mn 2+ /Mn 3+ transitions. Compared with 4 M KOH, the NMO@NF electrodes in 4 M LiOH electrolyte exhibited higher redox current density, suggesting improved electrochemical performance in LiOH solution. These results confirmed that the electrochemical properties of NMO@NF electrodes can be improved by choosing an appropriate electrolyte. Figure 4 (d) shows the specific capacity of the NMO@NF electrode as a function of scan rate used in cells containing 4 M KOH and 4 M LiOH electrolytes. The Randles Sevcik graph of the materials' anodic current against the square root of scan rate of the NMO@NF electrode in 4 M KOH, and 4 M LiOH is displayed in the inset of Fig. 4 (d). The redox reactions diffusion-controlled rate kinetics are shown by a straight line. That is, the fast redox changes at the electrode were outpacing the electrolyte charge transfer. The electrolyte's diffusion rate-controlled kinetics might also be responsible for the diminution in specific capacitance at high scan rates. The formula represents the Randles-Sevcik Eq. (1) [ 23 ]. I p = (2.69 × 10 5 ) × n 1.5 × A × C × D 0.5 ⋅ ʋ 0.5 (1) Ip plotted against the square root of the scan rate results in a straight line, with the slope being (2.69 × 10 5 ) × n 1.5 × A × C× D 0.5 × ʋ 0.5 . This makes it evident that diffusivity and slope are exactly related, and therefore, as diffusivity rises, so does specific capacitance [ 24 ]. Therefore, the sequence of 4 M LiOH > 4 M KOH applies to the diffusivity of charge transfer in the active electrode material. This outcome demonstrates unequivocally that the NMO@NF electrode outperformed the 4 M KOH electrolyte in the cell containing 4 M LiOH. The GCD curves of NMO@NF with cells containing 4 M LiOH and 4 M KOH electrolyte, respectively, at various current densities are provided in Fig. 5 (a) and Fig. 5 (b). The values of specific capacity for the NMO@NF electrode are 294 C g − 1 and 511 C g − 1 , and Columbic efficiencies are 94.2% and 98.4% in cells containing 4 M KOH and 4 M LiOH electrolytes, respectively, at a current density of 1 mA cm − 2 . The NMO@NF electrode's improved electrochemical performance is primarily due to its microporous nature and high surface area, which provide a large number of active sites at the electrode-electrolyte interface [ 25 ]. Figure 5 (c) displays the comparative GCD curves of NMO@NF electrodes in cells containing 4 M KOH and 4 M LiOH at a current density of 1 mA cm − 2 . The specific capacity of the NMO@NF electrode as a function of current density used in cells containing 4 M KOH and 4 M LiOH electrolytes is provided in Fig. 5 (d). The long-term cyclic performance of the NMO@NF electrode in a cell containing 4 M LiOH over 2000 cycles at a scan rate of 100 mV s − 1 was verified in Fig. 6 (b) . The calculated values of the specific capacitance of the NMO@NF electrode in a cell containing 4 M LiOH and 4 M KOH electrolytes by CV and GCD tests are summarized in Table 1 . The cyclic retention plot reveals that the specific capacity increases from the 1st cycle to 1350 cycles, after which it remains steady from 1350 cycles to 2000 cycles. The specific capacity has decreased from 551 C g − 1 for the first cycle to 549 C g − 1 after 2000 cycles. Hence, the NMO@NF electrode showed a less than 1% decrease in specific capacity from the initial value after 2000 cycles. According to the stability study, NMO@NF electrodes exhibit long-duration cyclic performance, which is very helpful for energy storage in supercapacitors. The comparative EIS plots of the NMO@NF electrode in a 4 M LiOH and 4 M KOH electrolyte are shown in Fig. 6 (a). The values of the internal resistance and charge transfer resistance of the NMO@NF electrode in 4 M LiOH and in 4 M KOH are R s = 3.3 Ω and 7.4 Ω, and R ct = 17 Ω and 78 Ω, respectively, which are revealed by the EIS plots as the interception of the Nyquist curves on the real impedance (Z) axis at the high-frequency region. The ability of electrode materials to store energy is improved by the smaller value of R S and R ct . Table 1 Summarized data of the specific capacity calculated from the CV plots and GCD plots by varying scan rates and current densities of the NM-Ni foam electrodes in a cell containing 4 M KOH, and 4 M LiOH electrolytes. Scan rates (mVs − 1 ) Specific capacity (C g − 1 ) by using CV plots Current density (mAcm − 2 ) Specific capacity (C g − 1 ) by using GCD plots KOH LiOH KOH LiOH 5 312 551 1 294 511 10 240 509 2 273.7 476 20 186 472 3 164 439 50 132 420 80 102 380 100 89 269 4. Conclusion In conclusion, highly crystalline micro-sized NiMn 2 O 4 nanostructures (NMO-NSs) were successfully synthesized via a simple hydrothermal method. The physico-chemical and electrochemical properties of the NMO@NF electrode, along with the influence of electrolyte composition, were systematically investigated. The mesoporous NMO@NF electrode exhibits a high specific capacity of 511 C g − 1 at a scan rate of 5 mV s − 1 in 4 M LiOH electrolyte. The electrochemical performance of the NMO@NF electrode in different electrolytes reveals superior behaviour in 4 M LiOH, which can be attributed to the smaller ionic radius and higher mobility of Li + ions. Additionally, the electrode demonstrates excellent cycling stability with long-term durability over 2000 cycles. The enhanced performance is mainly due to the synergistic effects of high surface area, a favourable pore structure, and efficient charge transfer. These findings highlight the critical role of electrolyte selection in optimizing electrode performance. Overall, the present study suggests that the hydrothermally synthesized NMO@NF electrode is a promising candidate for advanced high-energy storage applications. Declarations Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have influenced the work reported in this paper. Author Contribution Pragati N. Thonge: writing-original draft. validation, data curation, Suprimkumar D. Dhas: writing-original draft, writing-review and editing, methodology, Tushar T. Bhosale: conceptualization, methodology, Falah Awwad: funding acquisition, writing-review and editing, funding acquisition, Ramesh R. Tembhurne: validation, methodology, Manesh Yewale: Data curation, validation, and visualisation. Rameshwar R. Kothawale: Formal analysis, resources. Shivaji D. Waghmare: data curation and visualisation, Maheshkumar L. Mane: Conceptualisation, supervision. Annasaheb V. Moholkar: Writing-review and editing, supervision. Acknowledgement This research was supported by the United Arab Emirates University (UAEU), District 4.0 Postdoctoral Grant [Fund Code 12R325]. Pragati N. Thonge is thankful to the Chhatrapati Shahu Maharaj Research Training and Human Development Institute (SARTHI), Pune, Maharashtra, for providing funding for this project. The author, T. T. Bhosale, gratefully acknowledges the financial support received from BARTI under the BANRF Fellowship (BARTI/Fellowship/BANRF-2021/2135). Data availability Data will be made available on request. References J. Chmiola, C. Largeot, P. Taberna, P. Simon, Y. Gogotsi, Monolithic carbide-derived carbon films for micro-Supercapacitors. Science. 328 , 480 (2010). 10.1126/science N. Tanapongpisit, S. Wongprasod, P. Laohana, S. Kim, T. Butburee, W. Meevasana, S. Maensiri, C.W. Bark, W. Saenrang, Effects of the particle size of BaMnO 3 powders on the electrochemical performance of supercapacitor electrodes. Mater. Lett. 319 , 132258 (2022). 10.1016/j.matlet.2022.132258 B. Hu, Y. Wang, X. Shang, K. Xu, J. Yang, M. Huang, J. Liu, Structure-tunable Mn 3 O 4 -Fe 3 O 4 @C hybrids for high-performance supercapacitor. J. Colloid Interface Sci. 581 , 66–75 (2021). https://doi.org/10.1016/j.jcis.2020.07.094 S. Cheng, Z. Dai, J. Fu, P. Cui, K. Wei, Y. Zhang, Y. Wu, Y. Liu, Z. Sun, Z. Shao, X. Cui, Q. Su, E. Xie, Towards large-scale electrochemical energy storage in the marine environment with a highly-extensible paper-like seawater supercapacitor device. J. Mater. Chem. A 9 , 622–631 (2021). https://doi.org/10.1039/D0TA09643A F. Béguin, V. Presser, A. Balducci, E. Frackowiak, Carbons and electrolytes, for advanced supercapacitors. Adv. Mater. 26 , 2219–2251 (2014). https://doi.org/10.1002/adma.201304137Citations: . 1,898 A. Stott, M.O. Tas, E.Y. Matsubara, M.G. Masteghin, J.M. Rosolen, R.A. Sporea, S.R.P. Silva, Exceptional rate capability from carbon-encapsulated polyaniline supercapacitor electrodes. Energy Environ. Mater. 3 , 389–397 (2020). https://doi.org/10.1002/eem2.12083 H. Yu, L. Lu, T. Xu, T. Zhang, L. Yang, J. Zhang, M. Gu, L. Chen, T. Cai, A facile method for synthesis of Ni(OH) 2 @xRF with excellent electrochemical performances. Mater. Lett. 273 , 127867 (2020). 10.3390/nano12132216 W. Wang, S. Guo, I. Lee, K. Ahmed, J. Zhong, Z. Favors, F. Zaera, M. Ozkan, .Ozkan, Hydrous ruthenium oxide nanoparticles anchored to graphene and carbonnanotube hybrid foam for supercapacitors. Sci. Rep. 4 , 4452 (2014). DOIhttps://doi.org/10.1038/srep04452 M. Yu, N. Arsent'ev, A.V. Yu. Koval'ko, P.A. Shmigel, M.V. Tikhonov, Kalinina, NiMn 2 O 4 spinel as a material for supercapacitors with a pseudocapacity effect. Glass Phys. Chem. 43 , 376–379 (2017). https://doi.org/10.1134/S1087659617040022 H. Pang, J. Deng, S. Wang, S. Li, J. Du, J. Chena, J. Zhang, Facile synthesis of porous nickel manganite materials and their morphology effect on electrochemical properties. RSC Adv. 2 , 5930–5934 (2012). https://doi.org/10.1039/c2ra20245j J. Bhagwan, S. Rani, V. Sivasankaran, K.L. Yadav, Y. Sharma, Improved energy storage, magnetic and electrical properties of aligned, mesoporous and high aspect ratio nanofibers of spinel-NiMn 2 O 4 . Appl. Surf. Sci. 426 , 913–923 (2017). https://doi.org/10.1016/j.apsusc.2017.07.253 H. Nan, W. Ma, Z. Gu, B. Geng, X. Zhang, Hierarchical NiMn 2 O 4 @CNT nanocomposites for high-performance asymmetric supercapacitors. RSC Adv. 5 , 24607–24614 (2015). https://doi.org/10.1039/C5RA00979K M. George, A. Mary John, S.S. Nair, P.A. Joy, M.R. Anantharaman, Finite size effects on the structural and magnetic properties of sol-gel synthesized NiFe 2 O 4 powders. J. Magn. Magn. Mater. 302 , 190–195 (2006). https://doi.org/10.1016/j.jmmm.2005.08.029 S.D. Dhas, P.S. Maldar, M. D.Patil, M.R. Waikar, R.G. Sonkawade, A.V. Moholkar, Sol-gel synthesized nickel oxide nanostructures on nickel foam and nickel mesh for a targeted energy storage application. J. Energy Storage. 47 , 103658–103671 (2022). https://doi.org/10.1016/j.jallcom.2007.12.017 S.P. Jahromi, A. Pandikumar, B.T. Goh, Y.S. Lim, W.J. Basirun, H.N. Limc, N.M. Huang, Influence of particle size on performance of a nickel oxide nanoparticle-based supercapacitor. RSC Adv. 5 , 14010–14019 (2015). https://doi.org/10.1039/C4RA16776G T. Nandagopal, G. Balaji, S. Vadivel, Tuning the morphology and size of NiMoO 4 nanoparticles anchored on reduced graphene oxide (rGO) nanosheets: The optimized hybrid electrodes for high energy density asymmetric supercapacitors. J. Electroanal. Chem. 928 , 116944 (2023). https://doi.org/10.1016/j.jelechem.2022.116944 J. Yuan, W. Zeng, Fabrication of NiCo 2 S 4 /nickel foam composite electrodes by cyclic voltammetric deposition and their supercapacitor performance. Mater. Lett. 330 , 133338 (2023). https://doi.org/10.1016/j.matlet.2022.133338 P. Samanta, S. Ghosh, N.C. Murmu, T. Kuila, Effect of redox additive in aqueous electrolyte on the high specific capacitance of cation incorporated MnCo 2 O 4 @Ni(OH) 2 electrode materials for flexible symmetric supercapacitor, Compos. B. Eng. COMPOS PART B-ENG, 215 (2021) 108755. https://doi.org/10.1016/j.compositesb.2021.108755 J. Bhagwan, S. Rani, V. Sivasankaran, K.L. Yadav, Y. Sharma, Improved energy storage, magnetic and electrical properties of aligned, mesoporous and high aspect ratio nanofibers of spinel-NiMn 2 O 4 . Appl. Surf. Sci. 426 , 913–923 (2017). https://doi.org/10.1016/j.apsusc.2017.07.253 S.D. Dhas, P.S. Maldar, M.D. Patil, S.A. Mane, M.R. Waikar, R.G. Sonkawade, A.V. Moholkar, Fabrication of efficient electrochemical capacitors rooted in sol-gel derived NiMn 2 O 4 nanoparticles. J. Electroanal. Chem. 897 , 115548 (2021). https://doi.org/10.1016/j.jelechem.2021.115548 N. Abbasi, M. Moradi, S. Hajati, M.A. Kiani, In-situ growth of ultrathin Ni 6 MnO 8 nanosheets on nickel foam as a binder-free positive electrode for asymmetric supercapacitor: Effects of alkaline aqueous and redox additive electrolytes. J. Mol. Liq. 244 , 269–278 (2017). 10.1016/j.molliq.2017.09.018 S.D. Dhas, P.S. Maldar, M.D. Patil, S. A.Mane, M.R. Waikar, R.G. Sonkawade, A.V. Moholkar, Fabrication of efficient electrochemical capacitors rooted in sol-gel derived NiMn 2 O 4 nanoparticles. J. Electroanal. Chem. 897 , 115548–115557 (2021). https://doi.org/10.1039/C8QI00121A N. Hu, L. Huang, W. Gong, Shen High-Performance Asymmetric Supercapacitor Based on Hierarchical NiMn 2 O 4 @CoS Core–Shell Microspheres and Stereotaxically Constricted Graphene. ACS Sustainable Chem. Eng. 6 , 16933–16940 (2018). 10.1021/acssuschemeng.8b04265 S. Ghosh, R. Santhosh, S. Jeniffer, V. Raghavan, G. Jacob, K. Nanaji, P. Kollu, S.K. Jeong, A.N. Grace, Natural biomass-derived hard carbon and activated carbons as electrochemical supercapacitor electrodes. Sci. Repo. 9 , 16315 (2019). 10.1038/s41598-019-52006-x J.S. Lee, S.I. Kim, J.C. Yoon, J.H. Jang, Chemical vapour deposition of mesoporousgraphene nano-balls for supercapacitor. ACS Nano. 7 , 6047–6055 (2013). https://doi.org/10.1021/nn401850z 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. 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-9306053\",\"acceptedTermsAndConditions\":true,\"allowDirectSubmit\":true,\"archivedVersions\":[],\"articleType\":\"Research Article\",\"associatedPublications\":[],\"authors\":[{\"id\":621707719,\"identity\":\"92e537ba-fc52-4497-8d9c-f0493f2900b7\",\"order_by\":0,\"name\":\"Pragati N. Thonge\",\"email\":\"\",\"orcid\":\"\",\"institution\":\"Punyashlok Ahilyadevi Holkar, Solapur University,\",\"correspondingAuthor\":false,\"prefix\":\"\",\"firstName\":\"Pragati\",\"middleName\":\"N.\",\"lastName\":\"Thonge\",\"suffix\":\"\"},{\"id\":621707720,\"identity\":\"6e20200e-09f6-41f7-8a66-5a950d1c5f52\",\"order_by\":1,\"name\":\"Suprimkumar D. Dhas\",\"email\":\"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA/UlEQVRIiWNgGAWjYLCCBCAEAWkglgMxDjwgRYsxWEsCMfbAtCQ2IPjYgfyM3GMfHuakJa5tP/vwdkFNXfr8sMMPgbbYyek2YNdicCMveUbitpzEbWfSja1nHDucu/F2mgFQS7Kx2QEcWiRyjBkSt1UkbjuQxibNw3Ygd+PsBJCWA0ARXA6DaTn/DKjlX1264ez0D3i1MNwAawE67AbQFt425gR56Rz8thiceZcM1JJmvO3GM2Zr3r7DhhukcwoOJBjg9ot8e+5hxp/bkmW3nU9jvM3zrU5efnb65g8fKuzkcGlhYOBBtxes0gCXcmxa5BvwqR4Fo2AUjIKRCADnnGSA41gtMwAAAABJRU5ErkJggg==\",\"orcid\":\"\",\"institution\":\"United Arab Emirates University\",\"correspondingAuthor\":true,\"prefix\":\"\",\"firstName\":\"Suprimkumar\",\"middleName\":\"D.\",\"lastName\":\"Dhas\",\"suffix\":\"\"},{\"id\":621707721,\"identity\":\"afae9f86-741f-4fdd-bcdd-acd574df9956\",\"order_by\":2,\"name\":\"Tushar T. Bhosale\",\"email\":\"\",\"orcid\":\"\",\"institution\":\"Shivaji University\",\"correspondingAuthor\":false,\"prefix\":\"\",\"firstName\":\"Tushar\",\"middleName\":\"T.\",\"lastName\":\"Bhosale\",\"suffix\":\"\"},{\"id\":621707722,\"identity\":\"1fa63082-47ac-45f9-89aa-0eb5d32a7cca\",\"order_by\":3,\"name\":\"Falah Awwad\",\"email\":\"\",\"orcid\":\"\",\"institution\":\"United Arab Emirates University\",\"correspondingAuthor\":false,\"prefix\":\"\",\"firstName\":\"Falah\",\"middleName\":\"\",\"lastName\":\"Awwad\",\"suffix\":\"\"},{\"id\":621707723,\"identity\":\"e46d058f-4427-404c-b068-ae69576a36b6\",\"order_by\":4,\"name\":\"Ramesh R. Tembhurne\",\"email\":\"\",\"orcid\":\"\",\"institution\":\"Punyashlok Ahilyadevi Holkar, Solapur University,\",\"correspondingAuthor\":false,\"prefix\":\"\",\"firstName\":\"Ramesh\",\"middleName\":\"R.\",\"lastName\":\"Tembhurne\",\"suffix\":\"\"},{\"id\":621707724,\"identity\":\"a9465f4e-b784-4451-b9af-49f517c8a52c\",\"order_by\":5,\"name\":\"Rameshwar R. Kothawale\",\"email\":\"\",\"orcid\":\"\",\"institution\":\"Shri Shivaji Mahavidyalaya\",\"correspondingAuthor\":false,\"prefix\":\"\",\"firstName\":\"Rameshwar\",\"middleName\":\"R.\",\"lastName\":\"Kothawale\",\"suffix\":\"\"},{\"id\":621707725,\"identity\":\"f5241afe-1c02-429e-9bb8-1d6790afb113\",\"order_by\":6,\"name\":\"Shivaji D. Waghmare\",\"email\":\"\",\"orcid\":\"\",\"institution\":\"Shri Shivaji Mahavidyalaya\",\"correspondingAuthor\":false,\"prefix\":\"\",\"firstName\":\"Shivaji\",\"middleName\":\"D.\",\"lastName\":\"Waghmare\",\"suffix\":\"\"},{\"id\":621707726,\"identity\":\"9503a91b-6279-4e92-b99e-c5efdcd66e60\",\"order_by\":7,\"name\":\"Maheshkumar L. Mane\",\"email\":\"\",\"orcid\":\"\",\"institution\":\"Shikshan Maharshi Guruvarya R. G. Shinde Mahavidyalaya,\",\"correspondingAuthor\":false,\"prefix\":\"\",\"firstName\":\"Maheshkumar\",\"middleName\":\"L.\",\"lastName\":\"Mane\",\"suffix\":\"\"},{\"id\":621707728,\"identity\":\"40308108-1e34-48a7-8322-4d024ea97d81\",\"order_by\":8,\"name\":\"Manesh A. Yewale\",\"email\":\"\",\"orcid\":\"\",\"institution\":\"Yeungnam University\",\"correspondingAuthor\":false,\"prefix\":\"\",\"firstName\":\"Manesh\",\"middleName\":\"A.\",\"lastName\":\"Yewale\",\"suffix\":\"\"},{\"id\":621707729,\"identity\":\"5d583920-6847-413a-9d18-51806689b127\",\"order_by\":9,\"name\":\"Annasaheb V. Moholkar\",\"email\":\"\",\"orcid\":\"\",\"institution\":\"Shivaji University\",\"correspondingAuthor\":false,\"prefix\":\"\",\"firstName\":\"Annasaheb\",\"middleName\":\"V.\",\"lastName\":\"Moholkar\",\"suffix\":\"\"}],\"badges\":[],\"createdAt\":\"2026-04-02 18:08:21\",\"currentVersionCode\":1,\"declarations\":\"\",\"doi\":\"10.21203/rs.3.rs-9306053/v1\",\"doiUrl\":\"https://doi.org/10.21203/rs.3.rs-9306053/v1\",\"draftVersion\":[],\"editorialEvents\":[],\"editorialNote\":\"\",\"failedWorkflow\":false,\"files\":[{\"id\":106874517,\"identity\":\"83d20733-9038-4e70-a2ee-102f9c2cf679\",\"added_by\":\"auto\",\"created_at\":\"2026-04-14 10:18:58\",\"extension\":\"png\",\"order_by\":1,\"title\":\"Figure 1\",\"display\":\"\",\"copyAsset\":false,\"role\":\"figure\",\"size\":202487,\"visible\":true,\"origin\":\"\",\"legend\":\"\\u003cp\\u003eSchematic of the hydrothermal synthesis method for the formation of NMO-NSs\\u003c/p\\u003e\",\"description\":\"\",\"filename\":\"floatimage1.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-9306053/v1/bd8e4e6d788f0b6dd3edd295.png\"},{\"id\":106874518,\"identity\":\"cf95fae1-42bf-4680-9e16-925269284e2c\",\"added_by\":\"auto\",\"created_at\":\"2026-04-14 10:18:58\",\"extension\":\"png\",\"order_by\":2,\"title\":\"Figure 2\",\"display\":\"\",\"copyAsset\":false,\"role\":\"figure\",\"size\":272259,\"visible\":true,\"origin\":\"\",\"legend\":\"\\u003cp\\u003e\\u003cstrong\\u003e(a) \\u003c/strong\\u003eThe XRD pattern of NMO-NSs and NMO@NF electrode prepared by hydrothermal method. (Inside: Zoom image of XRD pattern NMO-NSs),\\u003cstrong\\u003e (b)\\u003c/strong\\u003e FE-SEM micrograph of NMO-NSs at magnification of × 25,000 and \\u003cstrong\\u003e(c) \\u003c/strong\\u003eEDX spectrum of NMO-NSs.\\u003c/p\\u003e\",\"description\":\"\",\"filename\":\"floatimage2.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-9306053/v1/005c68e35f5beced4caf7899.png\"},{\"id\":106961528,\"identity\":\"ad3c828b-4b74-4caa-99a9-7c0cbf265b77\",\"added_by\":\"auto\",\"created_at\":\"2026-04-15 09:25:54\",\"extension\":\"png\",\"order_by\":3,\"title\":\"Figure 3\",\"display\":\"\",\"copyAsset\":false,\"role\":\"figure\",\"size\":88362,\"visible\":true,\"origin\":\"\",\"legend\":\"\\u003cp\\u003e(a) N\\u003csub\\u003e2\\u003c/sub\\u003e adsorption-desorption isotherms recorded for the NMO-NSs. (b) BJH pore size distribution curve.\\u003c/p\\u003e\",\"description\":\"\",\"filename\":\"floatimage3.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-9306053/v1/0a034135484783a0a3ddfb7f.png\"},{\"id\":106874520,\"identity\":\"45abb6fe-441c-494f-8ce8-732d7ea0cba4\",\"added_by\":\"auto\",\"created_at\":\"2026-04-14 10:18:58\",\"extension\":\"png\",\"order_by\":4,\"title\":\"Figure 4\",\"display\":\"\",\"copyAsset\":false,\"role\":\"figure\",\"size\":292665,\"visible\":true,\"origin\":\"\",\"legend\":\"\\u003cp\\u003e(a) CV curves obtained for the various scan rates in 4 M LiOH electrolyte, (b) CV curves obtained for the various scan rates in 4 M KOH electrolyte, (c) Comparative CV Plot of the in 4 M LiOH and 4 M KOH electrolytes for the scan rates 100 mV s\\u003csup\\u003e-1\\u003c/sup\\u003e. (d) Comparative Plot of the Cs vs. scan rate in 4 M LiOH and 4 M KOH electrolytes,\\u003c/p\\u003e\",\"description\":\"\",\"filename\":\"floatimage4.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-9306053/v1/a43a248da04022221f39251f.png\"},{\"id\":106874522,\"identity\":\"4ee2c3ba-c34d-423e-8215-b3f177945a53\",\"added_by\":\"auto\",\"created_at\":\"2026-04-14 10:18:58\",\"extension\":\"png\",\"order_by\":5,\"title\":\"Figure 5\",\"display\":\"\",\"copyAsset\":false,\"role\":\"figure\",\"size\":206812,\"visible\":true,\"origin\":\"\",\"legend\":\"\\u003cp\\u003e\\u003cstrong\\u003e(a) \\u003c/strong\\u003eCD curves obtained for the various current densities in 4 M LiOH electrolyte, \\u003cstrong\\u003e(b) \\u003c/strong\\u003eCD curves obtained for the various current densities in 4 M KOH electrolyte, \\u003cstrong\\u003e(c) \\u003c/strong\\u003eComparative CD\\u003cstrong\\u003e \\u003c/strong\\u003ePlot of the in 4 M LiOH and 4 M KOH electrolytes for the current density of 1 mA cm\\u003csup\\u003e-2\\u003c/sup\\u003e. \\u003cstrong\\u003e\\u0026nbsp;(d) \\u003c/strong\\u003eComparative\\u003cstrong\\u003e \\u003c/strong\\u003ePlot of the Cs vs. current density in 4 M LiOH and 4 M KOH electrolytes.\\u003c/p\\u003e\",\"description\":\"\",\"filename\":\"floatimage5.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-9306053/v1/8195efcda270080cfad97698.png\"},{\"id\":106874521,\"identity\":\"d5257114-77b9-4fd3-9e5c-906bb6c1ba7a\",\"added_by\":\"auto\",\"created_at\":\"2026-04-14 10:18:58\",\"extension\":\"png\",\"order_by\":6,\"title\":\"Figure 6\",\"display\":\"\",\"copyAsset\":false,\"role\":\"figure\",\"size\":153648,\"visible\":true,\"origin\":\"\",\"legend\":\"\\u003cp\\u003e\\u003cstrong\\u003e(a) \\u003c/strong\\u003eEIS plots obtained for NMO@NF electrode in comparison of 4 M KOH and 4 M LiOH electrolytes. \\u003cstrong\\u003e(b) \\u003c/strong\\u003eCapacitance retention plot of NMO@NF electrode in 4 M LiOH electrolyte.\\u003c/p\\u003e\",\"description\":\"\",\"filename\":\"floatimage6.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-9306053/v1/df7b6e67d877bbe4b5d6153c.png\"},{\"id\":106963464,\"identity\":\"fbc2faaf-fbde-45f6-bc46-7e83ade8c530\",\"added_by\":\"auto\",\"created_at\":\"2026-04-15 09:44:39\",\"extension\":\"pdf\",\"order_by\":0,\"title\":\"\",\"display\":\"\",\"copyAsset\":false,\"role\":\"manuscript-pdf\",\"size\":1966925,\"visible\":true,\"origin\":\"\",\"legend\":\"\",\"description\":\"\",\"filename\":\"manuscript.pdf\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-9306053/v1/110a2d95-6eba-4658-ba66-ad728a8e1528.pdf\"}],\"financialInterests\":\"No competing interests reported.\",\"formattedTitle\":\"Effects of Electrolyte Substitution on the Electrochemical Performance of Spinel Nickel Manganese Oxide Nanostructures for Supercapacitor Applications\",\"fulltext\":[{\"header\":\"1. Introductions\",\"content\":\"\\u003cp\\u003eThe supercapacitors serve as a bridge between batteries and conventional capacitors due to their high specific power density, rapid charge-discharge performance, and excellent cycle life. The energy storage mechanism of the electrochemical capacitor depends on electric double-layer capacitors (EDLCs) and pseudocapacitors. Enhancing the interaction between the electrode and the electrolyte is necessary to improve the supercapacitive performance [\\u003cspan additionalcitationids=\\\"CR2 CR3\\\" citationid=\\\"CR1\\\" class=\\\"CitationRef\\\"\\u003e1\\u003c/span\\u003e\\u0026ndash;\\u003cspan citationid=\\\"CR4\\\" class=\\\"CitationRef\\\"\\u003e4\\u003c/span\\u003e]. The most important factors in producing high-performance supercapacitors are the quantity of active sites and the nature of the electrode nanomaterials, including increasing surface area to provide more active sites. To improve electrochemical performance, a few researchers have concentrated on increasing surface area by synthesizing porous nanomaterials [\\u003cspan citationid=\\\"CR5\\\" class=\\\"CitationRef\\\"\\u003e5\\u003c/span\\u003e\\u0026ndash;\\u003cspan citationid=\\\"CR6\\\" class=\\\"CitationRef\\\"\\u003e6\\u003c/span\\u003e].\\u003c/p\\u003e \\u003cp\\u003eDespite their low conductivity, spinel metal oxides (AB\\u003csub\\u003e2\\u003c/sub\\u003eO\\u003csub\\u003e4\\u003c/sub\\u003e) have been employed as electrode active materials due to the different oxidation states of the elements that can be substituted on A/B cation octahedral and tetrahedral sites, allowing for flexible chemical properties and various redox-active sites. Among different spinel metal oxides, NiMn\\u003csub\\u003e2\\u003c/sub\\u003eO\\u003csub\\u003e4\\u003c/sub\\u003e (NMO) has been only sparingly explored for supercapacitor applications [\\u003cspan citationid=\\\"CR7\\\" class=\\\"CitationRef\\\"\\u003e7\\u003c/span\\u003e\\u0026ndash;\\u003cspan citationid=\\\"CR8\\\" class=\\\"CitationRef\\\"\\u003e8\\u003c/span\\u003e].\\u003c/p\\u003e \\u003cp\\u003eSo far, NM-NSs have been synthesized in different forms by a variety of chemical routes such as sol-gel [\\u003cspan citationid=\\\"CR9\\\" class=\\\"CitationRef\\\"\\u003e9\\u003c/span\\u003e], co-precipitation method [\\u003cspan citationid=\\\"CR10\\\" class=\\\"CitationRef\\\"\\u003e10\\u003c/span\\u003e], electrospinning [\\u003cspan citationid=\\\"CR11\\\" class=\\\"CitationRef\\\"\\u003e11\\u003c/span\\u003e], and hydrothermal route, etc. [\\u003cspan citationid=\\\"CR12\\\" class=\\\"CitationRef\\\"\\u003e12\\u003c/span\\u003e]. The method used to synthesise NSs greatly influences their physicochemical properties. Therefore, economically viable, environmentally safe, fast-moving, and energy-efficient synthesis routes are essential for the mass production of NSs [\\u003cspan citationid=\\\"CR13\\\" class=\\\"CitationRef\\\"\\u003e13\\u003c/span\\u003e].\\u003c/p\\u003e \\u003cp\\u003eThe hydrothermal method is considered a versatile, cost-effective wet-chemical method. In this synthesis technique, by varying preparative parameters such as temperature, pH, and precursor molarity, the morphology and particle size of the materials can be controlled [\\u003cspan citationid=\\\"CR14\\\" class=\\\"CitationRef\\\"\\u003e14\\u003c/span\\u003e].\\u003c/p\\u003e \\u003cp\\u003eA streamlined active-material manufacturing process must be developed to produce supercapacitors on a large scale and at a reasonable cost. Here, we describe a hydrothermal method to make NMO-NSs and extensively examine the impact of the electrolytes (4 M KOH and 4 M LiOH) on their electrochemical features. The proposed supercapacitor electrodes in a cell containing 4 M LiOH begin to exhibit intriguing characteristics, including improved electrochemical performance due to the smaller ionic radius and slower nickel dissolution into the LiOH electrolyte. These might enable the fabrication of high-performance supercapacitors on a large scale.\\u003c/p\\u003e \\u003cp\\u003eThe current work focuses on the redox additive-assisted alkaline electrolyte as a new approach to enhance capacitance for supercapacitor applications, in light of current research trends on redox-active additives in aqueous electrolytes for supercapacitor applications. Here, the emphasis of NMO@NF is on using LiOH in the alkaline solution to increase the specific capacitance of the redox-active electrode in a safe and environmentally acceptable manner. NMO@NF displayed a typical redox potential between 0 and 0.7 V, which was enhanced by the particular reaction in the presence of LiOH electrolyte. A simple hydrothermal method was used to produce an easy-to-make, affordable cation-intercalated NMO@NF electrode. Ion movement was enhanced, and further support was provided for the intercalation/de-intercalation of the ions during the oxidation/reduction processes in LiOH over KOH by the spinel NMO. In a KOH and LiOH electrolyte, the as-prepared electrode with K\\u003csup\\u003e+\\u003c/sup\\u003e and Li\\u003csup\\u003e+\\u003c/sup\\u003e intercalated was measured to have a specific capacity. The NMO@NF electrode demonstrated a specific capacity of 511 Cg\\u003csup\\u003e\\u0026minus;\\u0026thinsp;1\\u003c/sup\\u003e at a scan rate of 5 mV s\\u003csup\\u003e\\u0026minus;\\u0026thinsp;1\\u003c/sup\\u003e and maintained its high electrochemical performance even after 2000 CV cycles. After 2000 CV cycles, the NMO@NF electrode demonstrated cyclic stability retention of up to 99% and 93% in 4 M LiOH and 4 M KOH electrolytes, respectively.\\u003c/p\\u003e\"},{\"header\":\"2. Experimental\",\"content\":\"\\u003cdiv id=\\\"Sec3\\\" class=\\\"Section2\\\"\\u003e \\u003ch2\\u003e2.1 Materials\\u003c/h2\\u003e \\u003cp\\u003eLithium hydroxide (LiOH), potassium hydroxide (KOH), manganese acetate (Mn(NO\\u003csub\\u003e3\\u003c/sub\\u003e)\\u003csub\\u003e2\\u003c/sub\\u003e.xH\\u003csub\\u003e2\\u003c/sub\\u003eO), nickel acetate (Ni(NO\\u003csub\\u003e3\\u003c/sub\\u003e)\\u003csub\\u003e2\\u003c/sub\\u003e.xH\\u003csub\\u003e2\\u003c/sub\\u003eO), methanol (CH\\u003csub\\u003e3\\u003c/sub\\u003eOH), Polyvinylidene fluoride (PVDF), NMP solvent, nickel foam (NF) and carbon black were purchased from Sigma Aldrich, India. All chemicals were of analytical grade and used without further purification.\\u003c/p\\u003e \\u003c/div\\u003e \\u003cdiv id=\\\"Sec4\\\" class=\\\"Section2\\\"\\u003e \\u003ch2\\u003e2.2 Characterization techniques\\u003c/h2\\u003e \\u003cp\\u003eThe X-ray diffraction (XRD) patterns of the NMO-NSs in the range of 2θ\\u0026thinsp;=\\u0026thinsp;15\\u003csup\\u003e0\\u003c/sup\\u003e to 80\\u003csup\\u003e0\\u003c/sup\\u003e were obtained with an X-ray D2 Phaser diffractometer, Bruker Ltd. (Germany), (Cu-Kα, λ\\u0026thinsp;=\\u0026thinsp;1.5405 \\u0026Aring;) instrument. Field emission scanning electron microscopy (FE-SEM) and energy-dispersive X-ray (EDS) elemental analysis were obtained on a JSM-6160 Jeol Ltd. (Japan). N\\u003csub\\u003e2\\u003c/sub\\u003e adsorption/desorption isotherms were obtained at Quantachrome NOVA 1000e (USA) to examine Brunauer\\u0026minus;Emmett\\u0026minus;Teller specific surface areas of the nanomaterial, and the pore size distribution was assessed via the fitting model established by Barrett\\u0026minus;Joyner\\u0026minus;Halenda (BJH). The electrochemical properties of the NMO@NF electrode were assessed through a three-electrode system in 4 M KOH and 4 M LiOH electrolytes using a Potentiostat (Model-VMP3-Bio-Logic, France).\\u003c/p\\u003e \\u003c/div\\u003e \\u003cdiv id=\\\"Sec5\\\" class=\\\"Section2\\\"\\u003e \\u003ch2\\u003e2.3 Synthesis of NMO-NSs by the hydrothermal method\\u003c/h2\\u003e \\u003cp\\u003eNiMn\\u003csub\\u003e2\\u003c/sub\\u003eO\\u003csub\\u003e4\\u003c/sub\\u003e (NMO) nanostructures were synthesized via a facile hydrothermal method. In a typical procedure, stoichiometric amounts of nickel acetate tetrahydrate (Ni(CH\\u003csub\\u003e3\\u003c/sub\\u003eCOO)\\u003csub\\u003e2\\u003c/sub\\u003e\\u0026middot;4H₂O) and manganese acetate tetrahydrate (Mn(CH\\u003csub\\u003e3\\u003c/sub\\u003eCOO)\\u003csub\\u003e2\\u003c/sub\\u003e\\u0026middot;4H₂O) were dissolved in a mixed solvent system of double-distilled water under constant stirring to form a homogeneous solution.\\u003c/p\\u003e \\u003cp\\u003e \\u003c/p\\u003e \\u003cp\\u003eThe resulting solution was transferred into a stainless-steel autoclave and maintained at 120\\u0026deg;C for 4 h. After naturally cooling to room temperature, the obtained precipitate was collected and thoroughly washed several times with double-distilled water and ethanol to remove residual impurities. The purified product was then dried at 60\\u0026deg;C and subsequently calcined in a muffle furnace at 500\\u0026deg;C for 4 h to obtain highly crystalline NiMn\\u003csub\\u003e2\\u003c/sub\\u003eO\\u003csub\\u003e4\\u003c/sub\\u003e nanostructures.\\u003c/p\\u003e \\u003c/div\\u003e \\u003cdiv id=\\\"Sec6\\\" class=\\\"Section2\\\"\\u003e \\u003ch2\\u003e2.4 Preparation of NMO-NF working electrode\\u003c/h2\\u003e \\u003cp\\u003eBefore electrode fabrication, nickel foam (NF) substrates (3 cm \\u0026times; 1 cm) were pretreated to remove surface impurities. The NF was ultrasonically cleaned in diluted hydrochloric acid (HCl) for 30 min, followed by repeated washing with ethanol and double-distilled water (DDW), and then dried under ambient conditions. The working electrodes were prepared by mixing the active material (NiMn\\u003csub\\u003e2\\u003c/sub\\u003eO\\u003csub\\u003e4\\u003c/sub\\u003e), carbon black, and polyvinylidene difluoride (PVDF) binder in a weight ratio of 8:1:1 using N-methyl-2-pyrrolidone (NMP) as the solvent to form a homogeneous slurry. The resulting slurry was uniformly coated onto the pretreated NF substrate, which served as the current collector. The coated electrodes were then dried overnight at 60\\u0026deg;C to ensure complete solvent removal and proper adhesion of the active material. The mass loading of the active material on the NF substrate was approximately 14 mg cm\\u003csup\\u003e\\u0026minus;\\u0026thinsp;2\\u003c/sup\\u003e. The prepared electrodes, denoted NMO\\u0026ndash;NF, were used for subsequent electrochemical measurements.\\u003c/p\\u003e \\u003c/div\\u003e \\u003cdiv id=\\\"Sec7\\\" class=\\\"Section2\\\"\\u003e \\u003ch2\\u003e2.5 Electrochemical analysis\\u003c/h2\\u003e \\u003cp\\u003eThe electrochemical measurements, cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance (EIS), were performed in 4 M KOH and 4 M LiOH electrolytes using a three-electrode arrangement on a VMP-3-based electrochemical workstation. A platinum plate and an SCE electrode were used as counter and reference electrodes, respectively. The Cs by CV and GCD, respectively, are calculated according to the following equations [\\u003cspan citationid=\\\"CR15\\\" class=\\\"CitationRef\\\"\\u003e15\\u003c/span\\u003e\\u0026ndash;\\u003cspan citationid=\\\"CR16\\\" class=\\\"CitationRef\\\"\\u003e16\\u003c/span\\u003e]:\\u003c/p\\u003e \\u003cp\\u003eC = \\u003cspan class=\\\"InlineEquation\\\"\\u003e\\u003cspan class=\\\"mathinline\\\"\\u003e\\\\(\\\\:\\\\frac{1}{\\\\text{M}V}{\\\\int\\\\:}_{{\\\\text{V}}_{\\\\text{i}}}^{{\\\\text{V}}_{\\\\text{f}}}\\\\text{I}\\\\:\\\\left(\\\\text{V}\\\\right)\\\\text{d}\\\\text{v}\\\\)\\u003c/span\\u003e\\u003c/span\\u003e (1)\\u003c/p\\u003e \\u003cp\\u003eCs = \\u003cspan class=\\\"InlineEquation\\\"\\u003e\\u003cspan class=\\\"mathinline\\\"\\u003e\\\\(\\\\:\\\\frac{\\\\text{I}\\\\varDelta\\\\:\\\\text{t}\\\\:}{M}\\\\)\\u003c/span\\u003e\\u003c/span\\u003e (2)\\u003c/p\\u003e \\u003cp\\u003ewhere C (F g\\u003csup\\u003e\\u0026minus;\\u0026thinsp;1\\u003c/sup\\u003e) is the specific capacity, I (mA) represents the discharge current, and M (mg) is the mass of active materials, \\u003cspan class=\\\"InlineEquation\\\"\\u003e\\u003cspan class=\\\"mathinline\\\"\\u003e\\\\(\\\\:\\\\text{V}\\\\)\\u003c/span\\u003e\\u003c/span\\u003e (V) is the scan rate and \\u003cspan class=\\\"InlineEquation\\\"\\u003e\\u003cspan class=\\\"mathinline\\\"\\u003e\\\\(\\\\:\\\\varDelta\\\\:\\\\text{t}\\\\)\\u003c/span\\u003e\\u003c/span\\u003e (sec) designates discharge and total discharge time.\\u003c/p\\u003e \\u003c/div\\u003e\"},{\"header\":\"3. Results and discussions\",\"content\":\"\\u003cp\\u003eThe XRD pattern \\u003cstrong\\u003e(\\u003c/strong\\u003eFig.\\u0026nbsp;\\u003cspan refid=\\\"Fig2\\\" class=\\\"InternalRef\\\"\\u003e2\\u003c/span\\u003ea\\u003cstrong\\u003e)\\u003c/strong\\u003e confirms the formation of a well-crystallized spinel NiMn\\u003csub\\u003e2\\u003c/sub\\u003eO\\u003csub\\u003e4\\u003c/sub\\u003e phase, with all diffraction peaks matching the standard ICDD data (Card No. 00-001-1110), indicating phase purity without any detectable impurities. The sharp and well-defined peaks corresponding to the (220), (311), (400), (511), and (533) planes suggest high crystallinity of the synthesized material. The FE-SEM image \\u003cstrong\\u003e(\\u003c/strong\\u003eFig.\\u0026nbsp;\\u003cspan refid=\\\"Fig2\\\" class=\\\"InternalRef\\\"\\u003e2\\u003c/span\\u003eb\\u003cstrong\\u003e)\\u003c/strong\\u003e reveals that the NMO nanostructures exhibit irregular grain-like morphology with rough surfaces, which can provide a large number of electrochemically active sites. Such surface features enhance electrolyte interaction and improve electrochemical performance. The observed structural and morphological features are expected to facilitate efficient ion transport and redox activity. The EDS analysis \\u003cstrong\\u003e(\\u003c/strong\\u003eFig.\\u0026nbsp;\\u003cspan refid=\\\"Fig2\\\" class=\\\"InternalRef\\\"\\u003e2\\u003c/span\\u003ec\\u003cstrong\\u003e)\\u003c/strong\\u003e confirms the presence of Ni, Mn, and O, with uniform distribution throughout the sample, verifying the successful formation of stoichiometric NiMn\\u003csub\\u003e2\\u003c/sub\\u003eO\\u003csub\\u003e4\\u003c/sub\\u003e without extraneous elements. Furthermore, the homogeneous elemental distribution indicates effective mixing of metal precursors during synthesis, which is crucial for achieving uniform electrochemical activity.\\u003c/p\\u003e\\n\\u003cp\\u003eIn addition, the absence of any impurity peaks in the XRD pattern and the consistent elemental composition from EDS analysis further validate the phase purity and compositional integrity of the material. The interconnected grain-like morphology may also contribute to improved electrical conductivity by providing continuous pathways for electron transport. Moreover, the rough and porous surface can enhance electrolyte penetration, thereby increasing the accessibility of active sites during redox reactions.\\u003c/p\\u003e\\n\\u003cp\\u003eOverall, the combined XRD, FE-SEM, and EDS results demonstrate the successful synthesis of phase-pure, highly crystalline, and morphologically favourable NiMn\\u003csub\\u003e2\\u003c/sub\\u003eO\\u003csub\\u003e4\\u003c/sub\\u003e nanostructures for electrochemical applications, particularly in energy storage systems.\\u003c/p\\u003e\\n\\u003cp\\u003eWhereas Fig. \\u003cspan refid=\\\"Fig3\\\" class=\\\"InternalRef\\\"\\u003e3\\u003c/span\\u003e\\u003cstrong\\u003e(a)\\u003c/strong\\u003e reveals the N\\u003csub\\u003e2\\u003c/sub\\u003e adsorption\\u0026ndash;desorption isotherms of the NMO-NSs. The Brunauer\\u0026ndash;Emmett\\u0026ndash;Teller (BET) specific surface area and average pore diameter (Fig. \\u003cspan refid=\\\"Fig3\\\" class=\\\"InternalRef\\\"\\u003e3\\u003c/span\\u003e\\u003cstrong\\u003e(b)\\u003c/strong\\u003e) of the NMO-NSs are nearly 46.13 m\\u003csup\\u003e2\\u003c/sup\\u003e g\\u003csup\\u003e\\u0026minus;\\u0026thinsp;1\\u003c/sup\\u003e and 6.75 nm, respectively, indicating that the hydrothermally synthesized NMO-NSs possess a relatively large surface area. The NMO-NSs exhibit a predominant mesoporous distribution in the pore size range of 2 to 10 nm, which is highly favourable for enhanced redox reactions and ion intercalation processes. Such mesoporous characteristics facilitate rapid diffusion of electrolyte ions and improve charge-transfer kinetics during electrochemical operation. Additionally, the increased surface area provides more active sites, thereby enhancing electrochemical performance.\\u003c/p\\u003e\\n\\u003cp\\u003eThe CV curves of the NMO@NF electrode in 4 M LiOH and 4 M KOH electrolytes are shown in Fig. \\u003cspan refid=\\\"Fig4\\\" class=\\\"InternalRef\\\"\\u003e4\\u003c/span\\u003e\\u003cstrong\\u003e(a) and 4(b)\\u003c/strong\\u003e, respectively, within the potential window of 0\\u0026ndash;0.7 V (vs. SCE) at different scan rates. The CV curves clearly exhibit more pronounced redox peaks in the LiOH electrolyte than in the KOH electrolyte, indicating a battery-type behaviour of the NMO@NF electrode. The presence of distinct redox peaks arises from Faradaic reactions occurring at the electrode-electrolyte interface [\\u003cspan citationid=\\\"CR17\\\" class=\\\"CitationRef\\\"\\u003e17\\u003c/span\\u003e].\\u003c/p\\u003e\\n\\u003cp\\u003eFurthermore, the CV curves reveal that the NMO@NF electrode in 4 M LiOH exhibits a larger enclosed area than that in 4 M KOH, suggesting superior charge storage capability. The calculated specific capacities are 312 C g\\u003csup\\u003e\\u0026minus;\\u0026thinsp;1\\u003c/sup\\u003e and 551 C g\\u003csup\\u003e\\u0026minus;\\u0026thinsp;1\\u003c/sup\\u003e for 4 M KOH and 4 M LiOH electrolytes, respectively, at a scan rate of 5 mV s\\u003csup\\u003e\\u0026minus;\\u0026thinsp;1\\u003c/sup\\u003e. The enhanced performance in LiOH can be attributed to the smaller ionic radius of Li\\u003csup\\u003e+\\u003c/sup\\u003e (0.09 nm) compared to K\\u003csup\\u003e+\\u003c/sup\\u003e (0.152 nm), which facilitates faster ion diffusion. Additionally, the larger hydrated radius of K\\u003csup\\u003e+\\u003c/sup\\u003e results in lower mobility in aqueous electrolytes, thereby limiting its electrochemical performance [\\u003cspan citationid=\\\"CR18\\\" class=\\\"CitationRef\\\"\\u003e18\\u003c/span\\u003e\\u0026ndash;\\u003cspan citationid=\\\"CR19\\\" class=\\\"CitationRef\\\"\\u003e19\\u003c/span\\u003e].\\u003c/p\\u003e\\n\\u003cp\\u003eThe following equations form the basis of the oxidation-reduction reactions of NiMn\\u003csub\\u003e2\\u003c/sub\\u003eO\\u003csub\\u003e4\\u003c/sub\\u003e in the alkaline KOH and LiOH electrolytes: [\\u003cspan citationid=\\\"CR21\\\" class=\\\"CitationRef\\\"\\u003e21\\u003c/span\\u003e\\u0026ndash;\\u003cspan citationid=\\\"CR22\\\" class=\\\"CitationRef\\\"\\u003e22\\u003c/span\\u003e].\\u003c/p\\u003e\\n\\u003cp\\u003eNiMn\\u003csub\\u003e2\\u003c/sub\\u003eO\\u003csub\\u003e4\\u003c/sub\\u003e\\u0026thinsp;+\\u0026thinsp;OH\\u003csup\\u003e\\u0026minus;\\u003c/sup\\u003e + H\\u003csub\\u003e2\\u003c/sub\\u003eO \\u0026harr; NiOOH\\u0026thinsp;+\\u0026thinsp;2MnOOH\\u0026thinsp;+\\u0026thinsp;2e\\u003csup\\u003e\\u0026minus;\\u003c/sup\\u003e \\u003cstrong\\u003e(1)\\u003c/strong\\u003e\\u003c/p\\u003e\\n\\u003cp\\u003eMnOOH\\u0026thinsp;+\\u0026thinsp;OH\\u003csup\\u003e\\u0026minus;\\u003c/sup\\u003e \\u0026harr; MnO\\u003csub\\u003e2\\u003c/sub\\u003e\\u0026thinsp;+\\u0026thinsp;H\\u003csub\\u003e2\\u003c/sub\\u003eO\\u0026thinsp;+\\u0026thinsp;e\\u003csup\\u003e\\u0026minus;\\u003c/sup\\u003e \\u003cstrong\\u003e(2)\\u003c/strong\\u003e\\u003c/p\\u003e\\n\\u003cp\\u003eTherefore, the improved electrochemical performance observed in LiOH electrolyte is mainly due to the smaller ionic size of Li\\u003csup\\u003e+\\u003c/sup\\u003e ions and reduced dissolution of nickel species, consistent with previous reports [\\u003cspan citationid=\\\"CR20\\\" class=\\\"CitationRef\\\"\\u003e20\\u003c/span\\u003e]. Figure\\u0026nbsp;\\u003cspan refid=\\\"Fig4\\\" class=\\\"InternalRef\\\"\\u003e4\\u003c/span\\u003e\\u003cstrong\\u003e(c)\\u003c/strong\\u003e shows the comparative CV curves of the NMO@NF electrode in both electrolytes at a scan rate of 100 mV s\\u003csup\\u003e\\u0026minus;\\u0026thinsp;1\\u003c/sup\\u003e. The presence of one oxidation peak during the anodic scan and one reduction peak during the cathodic scan confirms that the charge storage mechanism is dominated by Faradaic processes. These redox peaks are associated with the reversible Ni\\u003csup\\u003e2+\\u003c/sup\\u003e/Ni\\u003csup\\u003e3+\\u003c/sup\\u003e and Mn\\u003csup\\u003e2+\\u003c/sup\\u003e/Mn\\u003csup\\u003e3+\\u003c/sup\\u003e transitions.\\u003c/p\\u003e\\n\\u003cp\\u003eCompared with 4 M KOH, the NMO@NF electrodes in 4 M LiOH electrolyte exhibited higher redox current density, suggesting improved electrochemical performance in LiOH solution. These results confirmed that the electrochemical properties of NMO@NF electrodes can be improved by choosing an appropriate electrolyte. Figure \\u003cspan refid=\\\"Fig4\\\" class=\\\"InternalRef\\\"\\u003e4\\u003c/span\\u003e\\u003cstrong\\u003e(d)\\u003c/strong\\u003e shows the specific capacity of the NMO@NF electrode as a function of scan rate used in cells containing 4 M KOH and 4 M LiOH electrolytes.\\u003c/p\\u003e\\n\\u003cp\\u003eThe Randles Sevcik graph of the materials\\u0026apos; anodic current against the square root of scan rate of the NMO@NF electrode in 4 M KOH, and 4 M LiOH is displayed in the inset of Fig. \\u003cspan refid=\\\"Fig4\\\" class=\\\"InternalRef\\\"\\u003e4\\u003c/span\\u003e\\u003cstrong\\u003e(d).\\u003c/strong\\u003e The redox reactions diffusion-controlled rate kinetics are shown by a straight line. That is, the fast redox changes at the electrode were outpacing the electrolyte charge transfer. The electrolyte\\u0026apos;s diffusion rate-controlled kinetics might also be responsible for the diminution in specific capacitance at high scan rates. The formula represents the Randles-Sevcik Eq. (1) [\\u003cspan citationid=\\\"CR23\\\" class=\\\"CitationRef\\\"\\u003e23\\u003c/span\\u003e].\\u003c/p\\u003e\\n\\u003cp\\u003eI\\u003csub\\u003ep\\u003c/sub\\u003e = (2.69 \\u0026times; 10\\u003csup\\u003e5\\u003c/sup\\u003e) \\u0026times; n\\u003csup\\u003e1.5\\u003c/sup\\u003e\\u0026times; A \\u0026times; C \\u0026times; D\\u003csup\\u003e0.5\\u003c/sup\\u003e\\u0026sdot; ʋ \\u003csup\\u003e0.5\\u003c/sup\\u003e \\u003cstrong\\u003e(1)\\u003c/strong\\u003e\\u003c/p\\u003e\\n\\u003cp\\u003eIp plotted against the square root of the scan rate results in a straight line, with the slope being (2.69 \\u0026times; 10\\u003csup\\u003e5\\u003c/sup\\u003e) \\u0026times; n\\u003csup\\u003e1.5\\u003c/sup\\u003e\\u0026times; A \\u0026times; C\\u0026times; D\\u003csup\\u003e0.5\\u0026nbsp;\\u003c/sup\\u003e\\u0026times; ʋ \\u003csup\\u003e0.5\\u003c/sup\\u003e. This makes it evident that diffusivity and slope are exactly related, and therefore, as diffusivity rises, so does specific capacitance [\\u003cspan citationid=\\\"CR24\\\" class=\\\"CitationRef\\\"\\u003e24\\u003c/span\\u003e]. Therefore, the sequence of 4 M LiOH\\u0026thinsp;\\u0026gt;\\u0026thinsp;4 M KOH applies to the diffusivity of charge transfer in the active electrode material. This outcome demonstrates unequivocally that the NMO@NF electrode outperformed the 4 M KOH electrolyte in the cell containing 4 M LiOH.\\u003c/p\\u003e\\n\\u003cp\\u003eThe GCD curves of NMO@NF with cells containing 4 M LiOH and 4 M KOH electrolyte, respectively, at various current densities are provided in Fig. \\u003cspan refid=\\\"Fig5\\\" class=\\\"InternalRef\\\"\\u003e5\\u003c/span\\u003e\\u003cstrong\\u003e(a)\\u003c/strong\\u003e and Fig. \\u003cspan refid=\\\"Fig5\\\" class=\\\"InternalRef\\\"\\u003e5\\u003c/span\\u003e\\u003cstrong\\u003e(b).\\u003c/strong\\u003e The values of specific capacity for the NMO@NF electrode are 294 C g\\u003csup\\u003e\\u0026minus;\\u0026thinsp;1\\u003c/sup\\u003e and 511 C g\\u003csup\\u003e\\u0026minus;\\u0026thinsp;1\\u003c/sup\\u003e, and Columbic efficiencies are 94.2% and 98.4% in cells containing 4 M KOH and 4 M LiOH electrolytes, respectively, at a current density of 1 mA cm\\u003csup\\u003e\\u0026minus;\\u0026thinsp;2\\u003c/sup\\u003e. The NMO@NF electrode\\u0026apos;s improved electrochemical performance is primarily due to its microporous nature and high surface area, which provide a large number of active sites at the electrode-electrolyte interface [\\u003cspan citationid=\\\"CR25\\\" class=\\\"CitationRef\\\"\\u003e25\\u003c/span\\u003e]. Figure \\u003cspan refid=\\\"Fig5\\\" class=\\\"InternalRef\\\"\\u003e5\\u003c/span\\u003e\\u003cstrong\\u003e(c)\\u003c/strong\\u003e displays the comparative GCD curves of NMO@NF electrodes in cells containing 4 M KOH and 4 M LiOH at a current density of 1 mA cm\\u003csup\\u003e\\u0026minus;\\u0026thinsp;2\\u003c/sup\\u003e. The specific capacity of the NMO@NF electrode as a function of current density used in cells containing 4 M KOH and 4 M LiOH electrolytes is provided in Fig. \\u003cspan refid=\\\"Fig5\\\" class=\\\"InternalRef\\\"\\u003e5\\u003c/span\\u003e\\u003cstrong\\u003e(d).\\u003c/strong\\u003e The long-term cyclic performance of the NMO@NF electrode in a cell containing 4 M LiOH over 2000 cycles at a scan rate of 100 mV s\\u003csup\\u003e\\u0026minus;\\u0026thinsp;1\\u003c/sup\\u003e was verified in Fig. \\u003cspan refid=\\\"Fig6\\\" class=\\\"InternalRef\\\"\\u003e6\\u003c/span\\u003e\\u003cstrong\\u003e(b)\\u003c/strong\\u003e. The calculated values of the specific capacitance of the NMO@NF electrode in a cell containing 4 M LiOH and 4 M KOH electrolytes by CV and GCD tests are summarized in Table \\u003cspan refid=\\\"Tab1\\\" class=\\\"InternalRef\\\"\\u003e1\\u003c/span\\u003e. The cyclic retention plot reveals that the specific capacity increases from the 1st cycle to 1350 cycles, after which it remains steady from 1350 cycles to 2000 cycles. The specific capacity has decreased from 551 C g\\u003csup\\u003e\\u0026minus;\\u0026thinsp;1\\u003c/sup\\u003e for the first cycle to 549 C g\\u003csup\\u003e\\u0026minus;\\u0026thinsp;1\\u003c/sup\\u003e after 2000 cycles. Hence, the NMO@NF electrode showed a less than 1% decrease in specific capacity from the initial value after 2000 cycles. According to the stability study, NMO@NF electrodes exhibit long-duration cyclic performance, which is very helpful for energy storage in supercapacitors. The comparative EIS plots of the NMO@NF electrode in a 4 M LiOH and 4 M KOH electrolyte are shown in Fig. \\u003cspan refid=\\\"Fig6\\\" class=\\\"InternalRef\\\"\\u003e6\\u003c/span\\u003e\\u003cstrong\\u003e(a).\\u003c/strong\\u003e The values of the internal resistance and charge transfer resistance of the NMO@NF electrode in 4 M LiOH and in 4 M KOH are R\\u003csub\\u003es\\u003c/sub\\u003e = 3.3 Ω and 7.4 Ω, and R\\u003csub\\u003ect\\u003c/sub\\u003e = 17 Ω and 78 Ω, respectively, which are revealed by the EIS plots as the interception of the Nyquist curves on the real impedance (Z) axis at the high-frequency region. The ability of electrode materials to store energy is improved by the smaller value of R\\u003csub\\u003eS\\u003c/sub\\u003e and R\\u003csub\\u003ect\\u003c/sub\\u003e.\\u003c/p\\u003e\\n\\u003ctable float=\\\"Yes\\\" id=\\\"Tab1\\\" border=\\\"1\\\"\\u003e\\n \\u003ccaption language=\\\"En\\\"\\u003e\\n \\u003cdiv class=\\\"CaptionNumber\\\"\\u003eTable 1\\u003c/div\\u003e\\n \\u003cdiv class=\\\"CaptionContent\\\"\\u003e\\n \\u003cp\\u003eSummarized data of the specific capacity calculated from the CV plots and GCD plots by varying scan rates and current densities of the NM-Ni foam electrodes in a cell containing 4 M KOH, and 4 M LiOH electrolytes.\\u003c/p\\u003e\\n \\u003c/div\\u003e\\n \\u003c/caption\\u003e\\n \\u003cthead\\u003e\\n \\u003ctr\\u003e\\n \\u003cth align=\\\"left\\\" colname=\\\"c1\\\" morerows=\\\"1\\\" rowspan=\\\"2\\\"\\u003e\\n \\u003cp\\u003eScan rates\\u003c/p\\u003e\\n \\u003cp\\u003e(mVs\\u003csup\\u003e\\u0026minus;\\u0026thinsp;1\\u003c/sup\\u003e)\\u003c/p\\u003e\\n \\u003c/th\\u003e\\n \\u003cth align=\\\"left\\\" colspan=\\\"2\\\" nameend=\\\"c3\\\" namest=\\\"c2\\\"\\u003e\\n \\u003cp\\u003eSpecific capacity (C g\\u003csup\\u003e\\u0026minus;\\u0026thinsp;1\\u003c/sup\\u003e) by using CV plots\\u003c/p\\u003e\\n \\u003c/th\\u003e\\n \\u003cth align=\\\"left\\\" colname=\\\"c4\\\" morerows=\\\"1\\\" rowspan=\\\"2\\\"\\u003e\\n \\u003cp\\u003eCurrent density\\u003c/p\\u003e\\n \\u003cp\\u003e(mAcm\\u003csup\\u003e\\u0026minus;\\u0026thinsp;2\\u003c/sup\\u003e)\\u003c/p\\u003e\\n \\u003c/th\\u003e\\n \\u003cth align=\\\"left\\\" colspan=\\\"2\\\" nameend=\\\"c6\\\" namest=\\\"c5\\\"\\u003e\\n \\u003cp\\u003eSpecific capacity (C g\\u003csup\\u003e\\u0026minus;\\u0026thinsp;1\\u003c/sup\\u003e) by using GCD plots\\u003c/p\\u003e\\n \\u003c/th\\u003e\\n \\u003c/tr\\u003e\\n \\u003ctr\\u003e\\n \\u003cth align=\\\"left\\\" colname=\\\"c2\\\"\\u003e\\n \\u003cp\\u003e\\u003cstrong\\u003eKOH\\u003c/strong\\u003e\\u003c/p\\u003e\\n \\u003c/th\\u003e\\n \\u003cth align=\\\"left\\\" colname=\\\"c3\\\"\\u003e\\n \\u003cp\\u003e\\u003cstrong\\u003eLiOH\\u003c/strong\\u003e\\u003c/p\\u003e\\n \\u003c/th\\u003e\\n \\u003cth align=\\\"left\\\" colname=\\\"c5\\\"\\u003e\\n \\u003cp\\u003e\\u003cstrong\\u003eKOH\\u003c/strong\\u003e\\u003c/p\\u003e\\n \\u003c/th\\u003e\\n \\u003cth align=\\\"left\\\" colname=\\\"c6\\\"\\u003e\\n \\u003cp\\u003e\\u003cstrong\\u003eLiOH\\u003c/strong\\u003e\\u003c/p\\u003e\\n \\u003c/th\\u003e\\n \\u003c/tr\\u003e\\n \\u003c/thead\\u003e\\n \\u003ctbody\\u003e\\n \\u003ctr\\u003e\\n \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e\\n \\u003cp\\u003e5\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c2\\\"\\u003e\\n \\u003cp\\u003e312\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c3\\\"\\u003e\\n \\u003cp\\u003e551\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c4\\\"\\u003e\\n \\u003cp\\u003e1\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\" colname=\\\"c5\\\"\\u003e\\n \\u003cp\\u003e294\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c6\\\"\\u003e\\n \\u003cp\\u003e511\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003c/tr\\u003e\\n \\u003ctr\\u003e\\n \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e\\n \\u003cp\\u003e10\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c2\\\"\\u003e\\n \\u003cp\\u003e240\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c3\\\"\\u003e\\n \\u003cp\\u003e509\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c4\\\"\\u003e\\n \\u003cp\\u003e2\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\" colname=\\\"c5\\\"\\u003e\\n \\u003cp\\u003e273.7\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c6\\\"\\u003e\\n \\u003cp\\u003e476\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003c/tr\\u003e\\n \\u003ctr\\u003e\\n \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e\\n \\u003cp\\u003e20\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c2\\\"\\u003e\\n \\u003cp\\u003e186\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c3\\\"\\u003e\\n \\u003cp\\u003e472\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c4\\\"\\u003e\\n \\u003cp\\u003e3\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\" colname=\\\"c5\\\"\\u003e\\n \\u003cp\\u003e164\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c6\\\"\\u003e\\n \\u003cp\\u003e439\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003c/tr\\u003e\\n \\u003ctr\\u003e\\n \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e\\n \\u003cp\\u003e50\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c2\\\"\\u003e\\n \\u003cp\\u003e132\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c3\\\"\\u003e\\n \\u003cp\\u003e420\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\" colname=\\\"c4\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\" colname=\\\"c5\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\" colname=\\\"c6\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e\\n \\u003c/tr\\u003e\\n \\u003ctr\\u003e\\n \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e\\n \\u003cp\\u003e80\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c2\\\"\\u003e\\n \\u003cp\\u003e102\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c3\\\"\\u003e\\n \\u003cp\\u003e380\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\" colname=\\\"c4\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\" colname=\\\"c5\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\" colname=\\\"c6\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e\\n \\u003c/tr\\u003e\\n \\u003ctr\\u003e\\n \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e\\n \\u003cp\\u003e100\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c2\\\"\\u003e\\n \\u003cp\\u003e89\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c3\\\"\\u003e\\n \\u003cp\\u003e269\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\" colname=\\\"c4\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\" colname=\\\"c5\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\" colname=\\\"c6\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e\\n \\u003c/tr\\u003e\\n \\u003c/tbody\\u003e\\n\\u003c/table\\u003e\"},{\"header\":\"4. Conclusion\",\"content\":\"\\u003cp\\u003eIn conclusion, highly crystalline micro-sized NiMn\\u003csub\\u003e2\\u003c/sub\\u003eO\\u003csub\\u003e4\\u003c/sub\\u003e nanostructures (NMO-NSs) were successfully synthesized via a simple hydrothermal method. The physico-chemical and electrochemical properties of the NMO@NF electrode, along with the influence of electrolyte composition, were systematically investigated. The mesoporous NMO@NF electrode exhibits a high specific capacity of 511 C g\\u003csup\\u003e\\u0026minus;\\u0026thinsp;1\\u003c/sup\\u003e at a scan rate of 5 mV s\\u003csup\\u003e\\u0026minus;\\u0026thinsp;1\\u003c/sup\\u003e in 4 M LiOH electrolyte. The electrochemical performance of the NMO@NF electrode in different electrolytes reveals superior behaviour in 4 M LiOH, which can be attributed to the smaller ionic radius and higher mobility of Li\\u003csup\\u003e+\\u003c/sup\\u003e ions. Additionally, the electrode demonstrates excellent cycling stability with long-term durability over 2000 cycles. The enhanced performance is mainly due to the synergistic effects of high surface area, a favourable pore structure, and efficient charge transfer. These findings highlight the critical role of electrolyte selection in optimizing electrode performance. Overall, the present study suggests that the hydrothermally synthesized NMO@NF electrode is a promising candidate for advanced high-energy storage applications.\\u003c/p\\u003e\"},{\"header\":\"Declarations\",\"content\":\"\\u003cp\\u003e \\u003ch2\\u003eDeclaration of competing interest\\u003c/h2\\u003e \\u003cp\\u003eThe authors declare that they have no known competing financial interests or personal relationships that could have influenced the work reported in this paper.\\u003c/p\\u003e \\u003c/p\\u003e\\u003ch2\\u003eAuthor Contribution\\u003c/h2\\u003e\\u003cp\\u003ePragati N. Thonge: writing-original draft. validation, data curation, Suprimkumar D. Dhas: writing-original draft, writing-review and editing, methodology, Tushar T. Bhosale: conceptualization, methodology, Falah Awwad: funding acquisition, writing-review and editing, funding acquisition, Ramesh R. Tembhurne: validation, methodology, Manesh Yewale: Data curation, validation, and visualisation. Rameshwar R. Kothawale: Formal analysis, resources. Shivaji D. Waghmare: data curation and visualisation, Maheshkumar L. Mane: Conceptualisation, supervision. Annasaheb V. Moholkar: Writing-review and editing, supervision.\\u003c/p\\u003e\\u003ch2\\u003eAcknowledgement\\u003c/h2\\u003e\\u003cp\\u003eThis research was supported by the United Arab Emirates University (UAEU), District 4.0 Postdoctoral Grant [Fund Code 12R325]. Pragati N. Thonge is thankful to the Chhatrapati Shahu Maharaj Research Training and Human Development Institute (SARTHI), Pune, Maharashtra, for providing funding for this project. The author, T. T. Bhosale, gratefully acknowledges the financial support received from BARTI under the BANRF Fellowship (BARTI/Fellowship/BANRF-2021/2135).\\u003c/p\\u003e\\u003ch2\\u003eData availability\\u003c/h2\\u003e \\u003cp\\u003eData will be made available on request.\\u003c/p\\u003e\"},{\"header\":\"References\",\"content\":\"\\u003col\\u003e\\u003cli\\u003e\\u003cspan\\u003eJ. Chmiola, C. Largeot, P. Taberna, P. Simon, Y. Gogotsi, Monolithic carbide-derived carbon films for micro-Supercapacitors. Science. \\u003cb\\u003e328\\u003c/b\\u003e, 480 (2010). \\u003cspan class=\\\"ExternalRef\\\"\\u003e\\u003cspan class=\\\"RefSource\\\"\\u003e10.1126/science\\u003c/span\\u003e\\u003cspan address=\\\"10.1126/science\\\" targettype=\\\"DOI\\\" class=\\\"RefTarget\\\"\\u003e\\u003c/span\\u003e\\u003c/span\\u003e\\u003c/span\\u003e\\u003c/li\\u003e \\u003cli\\u003e\\u003cspan\\u003eN. Tanapongpisit, S. Wongprasod, P. Laohana, S. Kim, T. Butburee, W. Meevasana, S. Maensiri, C.W. Bark, W. Saenrang, Effects of the particle size of BaMnO\\u003csub\\u003e3\\u003c/sub\\u003e powders on the electrochemical performance of supercapacitor electrodes. Mater. Lett. \\u003cb\\u003e319\\u003c/b\\u003e, 132258 (2022). \\u003cspan class=\\\"ExternalRef\\\"\\u003e\\u003cspan class=\\\"RefSource\\\"\\u003e10.1016/j.matlet.2022.132258\\u003c/span\\u003e\\u003cspan address=\\\"10.1016/j.matlet.2022.132258\\\" targettype=\\\"DOI\\\" class=\\\"RefTarget\\\"\\u003e\\u003c/span\\u003e\\u003c/span\\u003e\\u003c/span\\u003e\\u003c/li\\u003e \\u003cli\\u003e\\u003cspan\\u003eB. Hu, Y. Wang, X. Shang, K. Xu, J. Yang, M. Huang, J. Liu, Structure-tunable Mn\\u003csub\\u003e3\\u003c/sub\\u003eO\\u003csub\\u003e4\\u003c/sub\\u003e-Fe\\u003csub\\u003e3\\u003c/sub\\u003eO\\u003csub\\u003e4\\u003c/sub\\u003e@C hybrids for high-performance supercapacitor. J. Colloid Interface Sci. \\u003cb\\u003e581\\u003c/b\\u003e, 66\\u0026ndash;75 (2021). \\u003cspan class=\\\"ExternalRef\\\"\\u003e\\u003cspan class=\\\"RefSource\\\"\\u003ehttps://doi.org/10.1016/j.jcis.2020.07.094\\u003c/span\\u003e\\u003cspan address=\\\"10.1016/j.jcis.2020.07.094\\\" targettype=\\\"DOI\\\" class=\\\"RefTarget\\\"\\u003e\\u003c/span\\u003e\\u003c/span\\u003e\\u003c/span\\u003e\\u003c/li\\u003e \\u003cli\\u003e\\u003cspan\\u003eS. Cheng, Z. Dai, J. Fu, P. Cui, K. Wei, Y. Zhang, Y. Wu, Y. Liu, Z. Sun, Z. Shao, X. Cui, Q. Su, E. Xie, Towards large-scale electrochemical energy storage in the marine environment with a highly-extensible paper-like seawater supercapacitor device. J. Mater. Chem. A \\u003cb\\u003e9\\u003c/b\\u003e, 622\\u0026ndash;631 (2021). \\u003cspan class=\\\"ExternalRef\\\"\\u003e\\u003cspan class=\\\"RefSource\\\"\\u003ehttps://doi.org/10.1039/D0TA09643A\\u003c/span\\u003e\\u003cspan address=\\\"10.1039/D0TA09643A\\\" targettype=\\\"DOI\\\" class=\\\"RefTarget\\\"\\u003e\\u003c/span\\u003e\\u003c/span\\u003e\\u003c/span\\u003e\\u003c/li\\u003e \\u003cli\\u003e\\u003cspan\\u003eF. B\\u0026eacute;guin, V. Presser, A. Balducci, E. Frackowiak, Carbons and electrolytes, for advanced supercapacitors. Adv. Mater. \\u003cb\\u003e26\\u003c/b\\u003e, 2219\\u0026ndash;2251 (2014). \\u003cspan class=\\\"ExternalRef\\\"\\u003e\\u003cspan class=\\\"RefSource\\\"\\u003ehttps://doi.org/10.1002/adma.201304137Citations:\\u003c/span\\u003e\\u003cspan address=\\\"10.1002/adma.201304137Citations:\\\" targettype=\\\"DOI\\\" class=\\\"RefTarget\\\"\\u003e\\u003c/span\\u003e\\u003c/span\\u003e. 1,898\\u003c/span\\u003e\\u003c/li\\u003e \\u003cli\\u003e\\u003cspan\\u003eA. Stott, M.O. Tas, E.Y. Matsubara, M.G. Masteghin, J.M. Rosolen, R.A. Sporea, S.R.P. Silva, Exceptional rate capability from carbon-encapsulated polyaniline supercapacitor electrodes. Energy Environ. Mater. \\u003cb\\u003e3\\u003c/b\\u003e, 389\\u0026ndash;397 (2020). \\u003cspan class=\\\"ExternalRef\\\"\\u003e\\u003cspan class=\\\"RefSource\\\"\\u003ehttps://doi.org/10.1002/eem2.12083\\u003c/span\\u003e\\u003cspan address=\\\"10.1002/eem2.12083\\\" targettype=\\\"DOI\\\" class=\\\"RefTarget\\\"\\u003e\\u003c/span\\u003e\\u003c/span\\u003e\\u003c/span\\u003e\\u003c/li\\u003e \\u003cli\\u003e\\u003cspan\\u003eH. Yu, L. Lu, T. Xu, T. Zhang, L. Yang, J. Zhang, M. Gu, L. Chen, T. Cai, A facile method for synthesis of Ni(OH)\\u003csub\\u003e2\\u003c/sub\\u003e@xRF with excellent electrochemical performances. Mater. Lett. \\u003cb\\u003e273\\u003c/b\\u003e, 127867 (2020). \\u003cspan class=\\\"ExternalRef\\\"\\u003e\\u003cspan class=\\\"RefSource\\\"\\u003e10.3390/nano12132216\\u003c/span\\u003e\\u003cspan address=\\\"10.3390/nano12132216\\\" targettype=\\\"DOI\\\" class=\\\"RefTarget\\\"\\u003e\\u003c/span\\u003e\\u003c/span\\u003e\\u003c/span\\u003e\\u003c/li\\u003e \\u003cli\\u003e\\u003cspan\\u003eW. Wang, S. Guo, I. Lee, K. Ahmed, J. Zhong, Z. Favors, F. Zaera, M. Ozkan, .Ozkan, Hydrous ruthenium oxide nanoparticles anchored to graphene and carbonnanotube hybrid foam for supercapacitors. Sci. Rep. \\u003cb\\u003e4\\u003c/b\\u003e, 4452 (2014). \\u003cspan class=\\\"ExternalRef\\\"\\u003e\\u003cspan class=\\\"RefSource\\\"\\u003eDOIhttps://doi.org/10.1038/srep04452\\u003c/span\\u003e\\u003cspan address=\\\"DOI10.1038/srep04452\\\" targettype=\\\"DOI\\\" class=\\\"RefTarget\\\"\\u003e\\u003c/span\\u003e\\u003c/span\\u003e\\u003c/span\\u003e\\u003c/li\\u003e \\u003cli\\u003e\\u003cspan\\u003eM. Yu, N. Arsent'ev, A.V. Yu. Koval'ko, P.A. Shmigel, M.V. Tikhonov, Kalinina, NiMn\\u003csub\\u003e2\\u003c/sub\\u003eO\\u003csub\\u003e4\\u003c/sub\\u003e spinel as a material for supercapacitors with a pseudocapacity effect. Glass Phys. Chem. \\u003cb\\u003e43\\u003c/b\\u003e, 376\\u0026ndash;379 (2017). \\u003cspan class=\\\"ExternalRef\\\"\\u003e\\u003cspan class=\\\"RefSource\\\"\\u003ehttps://doi.org/10.1134/S1087659617040022\\u003c/span\\u003e\\u003cspan address=\\\"10.1134/S1087659617040022\\\" targettype=\\\"DOI\\\" class=\\\"RefTarget\\\"\\u003e\\u003c/span\\u003e\\u003c/span\\u003e\\u003c/span\\u003e\\u003c/li\\u003e \\u003cli\\u003e\\u003cspan\\u003eH. Pang, J. Deng, S. Wang, S. Li, J. Du, J. Chena, J. Zhang, Facile synthesis of porous nickel manganite materials and their morphology effect on electrochemical properties. RSC Adv. \\u003cb\\u003e2\\u003c/b\\u003e, 5930\\u0026ndash;5934 (2012). \\u003cspan class=\\\"ExternalRef\\\"\\u003e\\u003cspan class=\\\"RefSource\\\"\\u003ehttps://doi.org/10.1039/c2ra20245j\\u003c/span\\u003e\\u003cspan address=\\\"10.1039/c2ra20245j\\\" targettype=\\\"DOI\\\" class=\\\"RefTarget\\\"\\u003e\\u003c/span\\u003e\\u003c/span\\u003e\\u003c/span\\u003e\\u003c/li\\u003e \\u003cli\\u003e\\u003cspan\\u003eJ. Bhagwan, S. Rani, V. Sivasankaran, K.L. Yadav, Y. Sharma, Improved energy storage, magnetic and electrical properties of aligned, mesoporous and high aspect ratio nanofibers of spinel-NiMn\\u003csub\\u003e2\\u003c/sub\\u003eO\\u003csub\\u003e4\\u003c/sub\\u003e. Appl. Surf. Sci. \\u003cb\\u003e426\\u003c/b\\u003e, 913\\u0026ndash;923 (2017). \\u003cspan class=\\\"ExternalRef\\\"\\u003e\\u003cspan class=\\\"RefSource\\\"\\u003ehttps://doi.org/10.1016/j.apsusc.2017.07.253\\u003c/span\\u003e\\u003cspan address=\\\"10.1016/j.apsusc.2017.07.253\\\" targettype=\\\"DOI\\\" class=\\\"RefTarget\\\"\\u003e\\u003c/span\\u003e\\u003c/span\\u003e\\u003c/span\\u003e\\u003c/li\\u003e \\u003cli\\u003e\\u003cspan\\u003eH. Nan, W. Ma, Z. Gu, B. Geng, X. Zhang, Hierarchical NiMn\\u003csub\\u003e2\\u003c/sub\\u003eO\\u003csub\\u003e4\\u003c/sub\\u003e@CNT nanocomposites for high-performance asymmetric supercapacitors. RSC Adv. \\u003cb\\u003e5\\u003c/b\\u003e, 24607\\u0026ndash;24614 (2015). \\u003cspan class=\\\"ExternalRef\\\"\\u003e\\u003cspan class=\\\"RefSource\\\"\\u003ehttps://doi.org/10.1039/C5RA00979K\\u003c/span\\u003e\\u003cspan address=\\\"10.1039/C5RA00979K\\\" targettype=\\\"DOI\\\" class=\\\"RefTarget\\\"\\u003e\\u003c/span\\u003e\\u003c/span\\u003e\\u003c/span\\u003e\\u003c/li\\u003e \\u003cli\\u003e\\u003cspan\\u003eM. George, A. Mary John, S.S. Nair, P.A. Joy, M.R. Anantharaman, Finite size effects on the structural and magnetic properties of sol-gel synthesized NiFe\\u003csub\\u003e2\\u003c/sub\\u003eO\\u003csub\\u003e4\\u003c/sub\\u003e powders. J. Magn. Magn. Mater. \\u003cb\\u003e302\\u003c/b\\u003e, 190\\u0026ndash;195 (2006). \\u003cspan class=\\\"ExternalRef\\\"\\u003e\\u003cspan class=\\\"RefSource\\\"\\u003ehttps://doi.org/10.1016/j.jmmm.2005.08.029\\u003c/span\\u003e\\u003cspan address=\\\"10.1016/j.jmmm.2005.08.029\\\" targettype=\\\"DOI\\\" class=\\\"RefTarget\\\"\\u003e\\u003c/span\\u003e\\u003c/span\\u003e\\u003c/span\\u003e\\u003c/li\\u003e \\u003cli\\u003e\\u003cspan\\u003eS.D. Dhas, P.S. Maldar, M. D.Patil, M.R. Waikar, R.G. Sonkawade, A.V. Moholkar, Sol-gel synthesized nickel oxide nanostructures on nickel foam and nickel mesh for a targeted energy storage application. J. Energy Storage. \\u003cb\\u003e47\\u003c/b\\u003e, 103658\\u0026ndash;103671 (2022). \\u003cspan class=\\\"ExternalRef\\\"\\u003e\\u003cspan class=\\\"RefSource\\\"\\u003ehttps://doi.org/10.1016/j.jallcom.2007.12.017\\u003c/span\\u003e\\u003cspan address=\\\"10.1016/j.jallcom.2007.12.017\\\" targettype=\\\"DOI\\\" class=\\\"RefTarget\\\"\\u003e\\u003c/span\\u003e\\u003c/span\\u003e\\u003c/span\\u003e\\u003c/li\\u003e \\u003cli\\u003e\\u003cspan\\u003eS.P. Jahromi, A. Pandikumar, B.T. Goh, Y.S. Lim, W.J. Basirun, H.N. Limc, N.M. Huang, Influence of particle size on performance of a nickel oxide nanoparticle-based supercapacitor. RSC Adv. \\u003cb\\u003e5\\u003c/b\\u003e, 14010\\u0026ndash;14019 (2015). \\u003cspan class=\\\"ExternalRef\\\"\\u003e\\u003cspan class=\\\"RefSource\\\"\\u003ehttps://doi.org/10.1039/C4RA16776G\\u003c/span\\u003e\\u003cspan address=\\\"10.1039/C4RA16776G\\\" targettype=\\\"DOI\\\" class=\\\"RefTarget\\\"\\u003e\\u003c/span\\u003e\\u003c/span\\u003e\\u003c/span\\u003e\\u003c/li\\u003e \\u003cli\\u003e\\u003cspan\\u003eT. Nandagopal, G. Balaji, S. Vadivel, Tuning the morphology and size of NiMoO\\u003csub\\u003e4\\u003c/sub\\u003e nanoparticles anchored on reduced graphene oxide (rGO) nanosheets: The optimized hybrid electrodes for high energy density asymmetric supercapacitors. J. Electroanal. Chem. \\u003cb\\u003e928\\u003c/b\\u003e, 116944 (2023). \\u003cspan class=\\\"ExternalRef\\\"\\u003e\\u003cspan class=\\\"RefSource\\\"\\u003ehttps://doi.org/10.1016/j.jelechem.2022.116944\\u003c/span\\u003e\\u003cspan address=\\\"10.1016/j.jelechem.2022.116944\\\" targettype=\\\"DOI\\\" class=\\\"RefTarget\\\"\\u003e\\u003c/span\\u003e\\u003c/span\\u003e\\u003c/span\\u003e\\u003c/li\\u003e \\u003cli\\u003e\\u003cspan\\u003eJ. Yuan, W. Zeng, Fabrication of NiCo\\u003csub\\u003e2\\u003c/sub\\u003eS\\u003csub\\u003e4\\u003c/sub\\u003e/nickel foam composite electrodes by cyclic voltammetric deposition and their supercapacitor performance. Mater. Lett. \\u003cb\\u003e330\\u003c/b\\u003e, 133338 (2023). \\u003cspan class=\\\"ExternalRef\\\"\\u003e\\u003cspan class=\\\"RefSource\\\"\\u003ehttps://doi.org/10.1016/j.matlet.2022.133338\\u003c/span\\u003e\\u003cspan address=\\\"10.1016/j.matlet.2022.133338\\\" targettype=\\\"DOI\\\" class=\\\"RefTarget\\\"\\u003e\\u003c/span\\u003e\\u003c/span\\u003e\\u003c/span\\u003e\\u003c/li\\u003e \\u003cli\\u003e\\u003cspan\\u003eP. Samanta, S. Ghosh, N.C. Murmu, T. Kuila, Effect of redox additive in aqueous electrolyte on the high specific capacitance of cation incorporated MnCo\\u003csub\\u003e2\\u003c/sub\\u003eO\\u003csub\\u003e4\\u003c/sub\\u003e@Ni(OH)\\u003csub\\u003e2\\u003c/sub\\u003e electrode materials for flexible symmetric supercapacitor, Compos. B. Eng. COMPOS PART B-ENG, 215 (2021) 108755. \\u003cspan class=\\\"ExternalRef\\\"\\u003e\\u003cspan class=\\\"RefSource\\\"\\u003ehttps://doi.org/10.1016/j.compositesb.2021.108755\\u003c/span\\u003e\\u003cspan address=\\\"10.1016/j.compositesb.2021.108755\\\" targettype=\\\"DOI\\\" class=\\\"RefTarget\\\"\\u003e\\u003c/span\\u003e\\u003c/span\\u003e\\u003c/span\\u003e\\u003c/li\\u003e \\u003cli\\u003e\\u003cspan\\u003eJ. Bhagwan, S. Rani, V. Sivasankaran, K.L. Yadav, Y. Sharma, Improved energy storage, magnetic and electrical properties of aligned, mesoporous and high aspect ratio nanofibers of spinel-NiMn\\u003csub\\u003e2\\u003c/sub\\u003eO\\u003csub\\u003e4\\u003c/sub\\u003e. Appl. Surf. Sci. \\u003cb\\u003e426\\u003c/b\\u003e, 913\\u0026ndash;923 (2017). \\u003cspan class=\\\"ExternalRef\\\"\\u003e\\u003cspan class=\\\"RefSource\\\"\\u003ehttps://doi.org/10.1016/j.apsusc.2017.07.253\\u003c/span\\u003e\\u003cspan address=\\\"10.1016/j.apsusc.2017.07.253\\\" targettype=\\\"DOI\\\" class=\\\"RefTarget\\\"\\u003e\\u003c/span\\u003e\\u003c/span\\u003e\\u003c/span\\u003e\\u003c/li\\u003e \\u003cli\\u003e\\u003cspan\\u003eS.D. Dhas, P.S. Maldar, M.D. Patil, S.A. Mane, M.R. Waikar, R.G. Sonkawade, A.V. Moholkar, Fabrication of efficient electrochemical capacitors rooted in sol-gel derived NiMn\\u003csub\\u003e2\\u003c/sub\\u003eO\\u003csub\\u003e4\\u003c/sub\\u003e nanoparticles. J. Electroanal. Chem. \\u003cb\\u003e897\\u003c/b\\u003e, 115548 (2021). \\u003cspan class=\\\"ExternalRef\\\"\\u003e\\u003cspan class=\\\"RefSource\\\"\\u003ehttps://doi.org/10.1016/j.jelechem.2021.115548\\u003c/span\\u003e\\u003cspan address=\\\"10.1016/j.jelechem.2021.115548\\\" targettype=\\\"DOI\\\" class=\\\"RefTarget\\\"\\u003e\\u003c/span\\u003e\\u003c/span\\u003e\\u003c/span\\u003e\\u003c/li\\u003e \\u003cli\\u003e\\u003cspan\\u003eN. Abbasi, M. Moradi, S. Hajati, M.A. Kiani, In-situ growth of ultrathin Ni\\u003csub\\u003e6\\u003c/sub\\u003eMnO\\u003csub\\u003e8\\u003c/sub\\u003e nanosheets on nickel foam as a binder-free positive electrode for asymmetric supercapacitor: Effects of alkaline aqueous and redox additive electrolytes. J. Mol. Liq. \\u003cb\\u003e244\\u003c/b\\u003e, 269\\u0026ndash;278 (2017). \\u003cspan class=\\\"ExternalRef\\\"\\u003e\\u003cspan class=\\\"RefSource\\\"\\u003e10.1016/j.molliq.2017.09.018\\u003c/span\\u003e\\u003cspan address=\\\"10.1016/j.molliq.2017.09.018\\\" targettype=\\\"DOI\\\" class=\\\"RefTarget\\\"\\u003e\\u003c/span\\u003e\\u003c/span\\u003e\\u003c/span\\u003e\\u003c/li\\u003e \\u003cli\\u003e\\u003cspan\\u003eS.D. Dhas, P.S. Maldar, M.D. Patil, S. A.Mane, M.R. Waikar, R.G. Sonkawade, A.V. Moholkar, Fabrication of efficient electrochemical capacitors rooted in sol-gel derived NiMn\\u003csub\\u003e2\\u003c/sub\\u003eO\\u003csub\\u003e4\\u003c/sub\\u003e nanoparticles. J. Electroanal. Chem. \\u003cb\\u003e897\\u003c/b\\u003e, 115548\\u0026ndash;115557 (2021). \\u003cspan class=\\\"ExternalRef\\\"\\u003e\\u003cspan class=\\\"RefSource\\\"\\u003ehttps://doi.org/10.1039/C8QI00121A\\u003c/span\\u003e\\u003cspan address=\\\"10.1039/C8QI00121A\\\" targettype=\\\"DOI\\\" class=\\\"RefTarget\\\"\\u003e\\u003c/span\\u003e\\u003c/span\\u003e\\u003c/span\\u003e\\u003c/li\\u003e \\u003cli\\u003e\\u003cspan\\u003eN. Hu, L. Huang, W. Gong, Shen High-Performance Asymmetric Supercapacitor Based on Hierarchical NiMn\\u003csub\\u003e2\\u003c/sub\\u003eO\\u003csub\\u003e4\\u003c/sub\\u003e@CoS Core\\u0026ndash;Shell Microspheres and Stereotaxically Constricted Graphene. ACS Sustainable Chem. Eng. \\u003cb\\u003e6\\u003c/b\\u003e, 16933\\u0026ndash;16940 (2018). \\u003cspan class=\\\"ExternalRef\\\"\\u003e\\u003cspan class=\\\"RefSource\\\"\\u003e10.1021/acssuschemeng.8b04265\\u003c/span\\u003e\\u003cspan address=\\\"10.1021/acssuschemeng.8b04265\\\" targettype=\\\"DOI\\\" class=\\\"RefTarget\\\"\\u003e\\u003c/span\\u003e\\u003c/span\\u003e\\u003c/span\\u003e\\u003c/li\\u003e \\u003cli\\u003e\\u003cspan\\u003eS. Ghosh, R. Santhosh, S. Jeniffer, V. Raghavan, G. Jacob, K. Nanaji, P. Kollu, S.K. Jeong, A.N. Grace, Natural biomass-derived hard carbon and activated carbons as electrochemical supercapacitor electrodes. Sci. Repo. \\u003cb\\u003e9\\u003c/b\\u003e, 16315 (2019). \\u003cspan class=\\\"ExternalRef\\\"\\u003e\\u003cspan class=\\\"RefSource\\\"\\u003e10.1038/s41598-019-52006-x\\u003c/span\\u003e\\u003cspan address=\\\"10.1038/s41598-019-52006-x\\\" targettype=\\\"DOI\\\" class=\\\"RefTarget\\\"\\u003e\\u003c/span\\u003e\\u003c/span\\u003e\\u003c/span\\u003e\\u003c/li\\u003e \\u003cli\\u003e\\u003cspan\\u003eJ.S. Lee, S.I. Kim, J.C. Yoon, J.H. Jang, Chemical vapour deposition of mesoporousgraphene nano-balls for supercapacitor. ACS Nano. \\u003cb\\u003e7\\u003c/b\\u003e, 6047\\u0026ndash;6055 (2013). \\u003cspan class=\\\"ExternalRef\\\"\\u003e\\u003cspan class=\\\"RefSource\\\"\\u003ehttps://doi.org/10.1021/nn401850z\\u003c/span\\u003e\\u003cspan address=\\\"10.1021/nn401850z\\\" 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\":\"info@researchsquare.com\",\"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\":\"Electrolyte substitution, NiMn2O4, Hydrothermal synthesis, Supercapacitor, Energy storage\",\"lastPublishedDoi\":\"10.21203/rs.3.rs-9306053/v1\",\"lastPublishedDoiUrl\":\"https://doi.org/10.21203/rs.3.rs-9306053/v1\",\"license\":{\"name\":\"CC BY 4.0\",\"url\":\"https://creativecommons.org/licenses/by/4.0/\"},\"manuscriptAbstract\":\"\\u003cp\\u003eA facile hydrothermal method was employed to synthesize NiMn\\u003csub\\u003e2\\u003c/sub\\u003eO\\u003csub\\u003e4\\u003c/sub\\u003e (NMO) nanostructures (NSs) for application as electrode materials in high-performance supercapacitors. The synthesised NMO-NSs were characterised by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS). Electrochemical performance was evaluated using cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS) in 4 M KOH and 4 M LiOH aqueous electrolytes. The NMO@NF electrode exhibited a high specific capacity of 511 C g\\u003csup\\u003e\\u0026minus;\\u0026thinsp;1\\u003c/sup\\u003e at a scan rate of 5 mV s\\u003csup\\u003e\\u0026minus;\\u0026thinsp;1\\u003c/sup\\u003e in 4 M LiOH electrolyte. Furthermore, the electrode demonstrated excellent cyclic stability with less than 1% degradation after 2000 cycles. These results highlight the significant influence of electrolyte selection on the electrochemical performance of NiMn\\u003csub\\u003e2\\u003c/sub\\u003eO\\u003csub\\u003e4\\u003c/sub\\u003e-based supercapacitors.\\u003c/p\\u003e\",\"manuscriptTitle\":\"Effects of Electrolyte Substitution on the Electrochemical Performance of Spinel Nickel Manganese Oxide Nanostructures for Supercapacitor Applications\",\"msid\":\"\",\"msnumber\":\"\",\"nonDraftVersions\":[{\"code\":1,\"date\":\"2026-04-14 10:18:53\",\"doi\":\"10.21203/rs.3.rs-9306053/v1\",\"editorialEvents\":[{\"type\":\"communityComments\",\"content\":0}],\"status\":\"published\",\"journal\":{\"display\":true,\"email\":\"info@researchsquare.com\",\"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\":\"de53a55f-21e9-409a-b607-9384ac1288df\",\"owner\":[],\"postedDate\":\"April 14th, 2026\",\"published\":true,\"recentEditorialEvents\":[{\"type\":\"decision\",\"content\":\"Revision requested\",\"date\":\"2026-05-03T16:20:47+00:00\",\"index\":\"\",\"fulltext\":\"\"}],\"rejectedJournal\":[],\"revision\":\"\",\"amendment\":\"\",\"status\":\"posted\",\"subjectAreas\":[],\"tags\":[],\"updatedAt\":\"2026-05-03T16:23:59+00:00\",\"versionOfRecord\":[],\"versionCreatedAt\":\"2026-04-14 10:18:53\",\"video\":\"\",\"vorDoi\":\"\",\"vorDoiUrl\":\"\",\"workflowStages\":[]},\"version\":\"v1\",\"identity\":\"rs-9306053\",\"journalConfig\":\"researchsquare\"},\"__N_SSP\":true},\"page\":\"/article/[identity]/[[...version]]\",\"query\":{\"redirect\":\"/article/rs-9306053\",\"identity\":\"rs-9306053\",\"version\":[\"v1\"]},\"buildId\":\"XKTyCvWXoU3ODBz1xrDgd\",\"isFallback\":false,\"isExperimentalCompile\":false,\"dynamicIds\":[84888],\"gssp\":true,\"scriptLoader\":[]}","source_license":"CC-BY-4.0","license_restricted":false}