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Our study presents a facile hydrothermal approach for synthesizing NiMn2O4 and NiMn2O4/C nanostructures (NSs) intended for implementation as electrode materials in high-performance supercapacitors. The NiMn2O4 and NiMn2O4/C NSs synthesized via the hydrothermal method were comprehensively characterized using XRD, FE-SEM, FT-IR, XPS, and BET. Subsequently, the electrochemical performance of both NiMn2O4 and NiMn2O4/C was evaluated via CV, GCD, and EIS in 2 M KOH aqueous electrolyte. Our results demonstrate that the NiMn2O4/C electrode revealed a substantial specific capacitance/capacity of 789.3 F g–1/552.5 C g–1 at a scan rate of 5 mV s–1. Furthermore, the NiMn2O4/C electrode maintained a specific capacity retention of less than 4% after 5000 cycles. When coupled with an activated carbon (AC) electrode, the NiMn2O4/C//AC configuration exhibited a notable specific capacitance/capacity of 101.6 F g–1/162.5 C g–1, accompanied by a high energy density of 36.11 W h kg–1 at a power density of 1000 W kg–1, and sustained excellent cyclic stability (84% retention after 5000 cycles). Additionally, electrochemical analysis revealed an overpotential of 199 mV at 50 mA cm–2 and a minimal Tafel slope of 89 mV dec–1 for the oxygen evolution reaction (OER), suggesting the suitability of the NiMn2O4/C electrode for alkaline water electrocatalysis. Prolonged chronopotentiometry investigations at 100 mA cm–2 over 24 h further demonstrated a remarkable 97.3% retention of the OER activity. [ABSTRACT FROM AUTHOR]

In this work, Ni3V2O8 (NVO) and Ni3V2O8-reduced graphene oxide (NVO-rGO) are synthesized hydrothermally, and their extensive structural, morphological, and electrochemical characterizations follow subsequently. The synthetic materials' crystalline structure was confirmed by X-ray diffraction (XRD), and its unique marigold-like morphology was observed by field emission scanning electron microscopy (FESEM). The chemical states of the elements were investigated via X-ray photoelectron spectroscopy (XPS). Electrochemical impedance spectroscopy (EIS), Galvanostatic charge–discharge (GCD), and cyclic voltammetry (CV) were used to assess the electrochemical performance. A specific capacitance of 132 F/g, an energy density of 5.04 Wh/kg, and a power density of 187 W/kg were demonstrated by Ni3V2O8-rGO. Key electrochemical characteristics were b = 0.67; a transfer coefficient of 0.52; a standard rate constant of 6.07 × 10−5 cm/S; a diffusion coefficient of 5.27 × 10−8 cm2/S; and a series resistance of 1.65 Ω. By employing Ni3V2O8-rGO and activated carbon, an asymmetric supercapacitor with a specific capacitance of 7.85 F/g, an energy density of 3.52 Wh/kg, and a power density of 225 W/kg was achieved. The series resistance increased from 4.27 Ω to 6.63 Ω during cyclic stability tests, which showed 99% columbic efficiency and 87% energy retention. The potential of Ni3V2O8-rGO as a high-performance electrode material for supercapacitors is highlighted by these findings. [ABSTRACT FROM AUTHOR]

Surface microstructure modification of metal oxides also improves the electrochemical performance of metal oxide nanoparticles. The present investigation demonstrates how varying the urea molar content during the hydrothermal process altered the surfaces of MnCo2O4 nanoparticles. Successive increases of 0.1 M in urea concentration transformed the surface shape of MnCo2O4 nanoparticles from flower-like to sheet-like microstructures. Excellent electrochemical performance of MnCo2O4 nanoparticles was demonstrated in an aqueous 1 M KOH electrolyte. The improved MnCo2O4 nanoparticles have been employed to develop an asymmetric supercapacitor (ASC). The ASC device exhibits an energy density of 13 Wh/kg at a power density of 553 W/kg and a specific capacitance of 29 F g−1 at a current density of 4 mA/cm2. The MnCo2O4 nanoparticle electrode demonstrates remarkable electrocatalytic activity in both HER and OER. The MnCo2O4 electrode shows overpotential for HER and OER at 356 mV and 1.46 V, respectively. The Tafel slopes for HER and OER of the MnCo2O4 electrode are 356 mV/dec and 187 mV/dec, respectively. [ABSTRACT FROM AUTHOR]

The hydrothermal method has been utilized to synthesize graphitic carbon nitride (g-C3N4) polymers and cobalt oxide composites effectively. The weight percentage of g-C3N4 nanoparticles influenced the electrochemical performance of the Co3O4-g-C3N4 composite. In an aqueous electrolyte, the Co3O4-g-C3N4 composite electrode, produced with 150 mg of g-C3N4 nanoparticles, revealed remarkable electrochemical performance. With an increase in the weight percentage of g-C3N4 nanoparticles, the capacitive contribution of the Co3O4-g-C3N4 composite electrode increased. The Co3O4-g-C3N4-150 mg composite electrode shows a specific capacitance of 198 F/g. The optimized electrode, activated carbon, and polyvinyl alcohol gel with potassium hydroxide were used to develop an asymmetric supercapacitor. At a current density of 5 mA/cm2, the asymmetric supercapacitor demonstrated exceptional energy storage capacity with remarkable energy density and power density. The device retained great capacity over 6k galvanostatic charge–discharge (GCD) cycles, with no rise in series resistance following cyclic stability. The columbic efficiency of the asymmetric supercapacitor was likewise high. [ABSTRACT FROM AUTHOR]

In present research, walnut like copper sulfide is prepared via a facile single‐step potentiostatic electrodeposition method on conducting stainless steel substrate. The walnut like morphology of copper sulfide thin film lies of microplates and further microplates converted to nanogranuals, by means of a change in deposition time and thickness. Copper sulfide thin film electrode reveals a specific capacitance of 132 F g−1 at 50 mA cm−2. The film thickness changes with deposition time. The films acquire maximum thickness of 610 nm for 25 min of deposition. X‐ray diffraction analysis revels that the CuS thin films is polycrystalline in nature and the crystallite size is 29 nm. The peak at 612 cm−1 in the Fourier transform infrared spectroscopy spectra confirms the formation of CuS. The wettability study shows the hydrophilic nature, the contact angle of water with CuS electrode is 66°, and the charge transfer resistance of CuS electrode is 7.78 Ω. [ABSTRACT FROM AUTHOR]

In this paper, we present an effortless hydrothermal method for depositing niobium and manganese composite oxides onto Ni-foam. The formation of the desired NbMn-oxide phase is confirmed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analytical tools. In the study, we systematically investigated the effect of varying Mn concentrations on the physicochemical properties and energy storage performance of the NbMn-oxide composite. The NbMn-oxide exhibited nanoplates assembled from sphere-shaped structures along with irregularly shaped rectangular blocks of nano/micro-structures, forming a porous framework. The electrode with an Mn concentration of 0.02 M displayed an areal capacitance of approximately 5987.8 mF/cm2 and an energy density of 0.13 mWh/cm2, even at a high current density of 10 mA/cm2. Additionally, the hydrogen evolution reaction (HER) performance of the NbMn-oxide composite electrode was evaluated and it exhibited an overpotential of 86 mV to achieve a current density of 10 mA/cm². The electrode also displayed stable performance for approximately 7 h, with only a slight increase in overpotential from − 0.218 to − 0.263 V against the reversible hydrogen electrode (RHE) during the stability test. The investigation of charge storage kinetics revealed the dominance of the diffusion process over the capacitive process, with the quasi-reversible redox reactions in the composite metal-oxides responsible for the high electrochemical performance. The assembled asymmetric supercapacitor device, utilizing NbMn-2 (positive) and activated carbon (negative) electrodes, demonstrated an impressive energy density of 0.20 mWh/cm2 at a power density of 3.75 mW/cm2, coupled with exceptional cyclability (97%). These findings highlight the potential of Nb-based composite electrodes for both supercapacitor and HER water-splitting applications and underscore their significant potential for electrochemical energy conversion and storage. [Display omitted] • Effect of varying Mn on NbMn-oxide properties and energy storage studied, informing optimization for desired performance. • NbMn-oxide displayed nano/micro-structures for efficient energy storage and conversion. • Asymmetric device with NbMn-oxide (+ve) & activated carbon (-ve) electrodes showed noticeable electrochemical performance.. • NbMn-oxide composite electrode showed stable HER performance for 7 hrs, indicating potential for water splitting. • Diffusive dominance drives high electrochemical performance in composite metal oxides, surpassing capacitive processes. [ABSTRACT FROM AUTHOR]