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Despite their high specific capacitances, metal oxide-based electrodes still do not meet the commercial standard for cycling stability owing to their inherent poor electronic conductivity and morphological structural changes during charging and discharging. A superior specific capacitance, accompanied with long-term cycling durability, is pivotal for supercapacitor application. In this research article, different precursor volume ratios of copper–nickel solution were used for the construction of binder-free 3D marigold flower-like copper–nickel oxide (3D-MCuNi oxide) electrodes via a hydrothermal method. XPS, EDAX, and TEM studies reveal that the increased amount of O-vacancies in the marigold flowers of the copper–nickel oxide composite is caused by a significant number of imperfections in the structure and might enhance their electrical conductivity. The marigold flower-like morphological structure exhibits electrode–electrolyte ions with significantly high hydrophilicity and better electrochemical diffusion performance. The optimized volume ratio of Cu : Ni = 1 : 1 for 3D-MCuNi oxide composite nanomaterials demonstrates an excellent specific capacitance of 2387.15 F g−1 at a current density of 0.6 mA cm−2 and 93% cycling capacitive retention performance up to 10 000 cycles. Additionally, a flexible hybrid supercapacitor device (HSD) was assembled using reduced graphene oxide (rGO) and 3D-MCuNi oxide as the negative and positive electrode, respectively, which revealed excellent electrochemical charge storage performance with a high energy density of 120.9 W h kg−1, power density of 34.82 kW kg−1, and superior cycling stability of 87% retention. Thus, the 3D-MCuNi oxide composite potential materials are more attractive for charge storage supercapacitor applications. [ABSTRACT FROM AUTHOR]

Developing a cost-effective, highly efficient electrocatalyst for the hydrogen evolution reaction (HER) is a major challenge. Herein, we developed metallic molybdenum dioxide (MoO2) films on a stainless steel (SS) substrate by a simple one-step hydrothermal process employing citric acid as a chelating agent. The experiment was carried out with different concentrations of the precursor solution. The porous and compactly arranged interconnected micro-sheets are shown by a MoO2 that enhances the HER in the acidic electrolyte. Its electrochemical study showed excellent water-splitting activity with more than 9 h of stability. The low onset potential of 60 mV and overpotential of 162 mV vs RHE at a current density of 10 mA/cm2 makes this electrode an efficient electro-catalyst for HER. Also, the use of low-cost substrates like SS and normal air annealing, makes the MoO2 sample, cost-effective and better for practical application. [ABSTRACT FROM AUTHOR]

The charge storage application has witnessed a dramatic increase in terms of the short charge–discharge time of supercapacitors, specifically in highly active electrode materials. For charge storage supercapacitor applications, highly porous materials are preferable. In this research article, thiourea acts as a leaving agent in the preparation of the porous 3D spherical architecture of NiO nanomaterials. The influence of the molar concentration of thiourea on structural, morphological, and electrochemical charge storage applications has been studied. X-ray diffraction reveals a cubic structure with Fm3¯m space group for the NiO nanomaterials. The scanning electron microscopy (SEM) images show the porous 3D columnar spherical structure, and FTIR has been used for the optical analysis of the NiO materials. The 1D–3D columnar-spherical structure of the NiO flakes exhibits a high electrochemical charge storage pseudocapacitive nature. The optimized 0.40 M thiourea–NiO (Th–NiO) nanomaterial is highly hydrophilic, exhibiting a maximum specific capacity of 171.1 mA h g−1 at 5 mV s−1 by CV and 148.5 mA h g−1 at 0.2 mA cm−2 by GCD. The highest power, energy densities are 0.96 kW kg−1 and 6.66 W h kg−1 with the highest charge–discharge cycle rating of 92% up to 5000 cycles of the asymmetric NiO//rGO hybrid supercapacitor device. [ABSTRACT FROM AUTHOR]

Metallic molybdenum dioxide (MoO2) films were grown on stainless steel (SS) substrate by a simple hydrothermal process employing citric acid at different deposition times that acts as a chelating agent. The tuning of the bandgap of SS and MoO2 favours the water splitting which could not be obtained on other conventional substrates. Initially, the morphology of MoO2 was aggregated ultrathin nanosheets for a six-hour reaction time, and it changed to other diverse morphology by varying the reaction time. XRD data confirm the formation of MoO2 nanoparticles. The electrochemical water activation studies show that 10-h (M10) MoO2 film on SS is showing an excellent hydrogen evolution reaction (HER) catalyst with good stability (9 h). MoO2 on SS displays a low onset overpotential of − 33 mV vs RHE with a Tafel slope of 39 mV/dec and − 138 mV vs RHE overpotential at 10 mA/cm2 current density. The large active surface area and lesser electrochemical charge-transfer resistance offered by the MoO2 nanostructures play a major role in the enhanced HER activity. [ABSTRACT FROM AUTHOR]