Currently, energy storage devices draw considerable attention owing to the growing need for clean energy. The depletion of fossil fuels and the generation of greenhouse gases have led to the development of alternative, environmentally friendly energy storage devices. Supercapacitors with high power densities are excellent devices for energy storage. Although carbon-based materials are widely used in such devices, their non-faradic behavior in electrical double layer capacitors (EDLCs) limits the maximum power density that can be generated. In contrast, the faradaic mechanism of transition metal hydroxides results in better capacitance rates along with good stability during cycling. This review is confined to nickel cobalt layered double hydroxides (NiCo LDHs) classified based on the fabrication of electrodes for application in supercapacitors. We discuss the growth of the active LDH material in situ or ex situ on the current collector and how the synthesis can affect the crystal structure as well as the electrochemical performance of the electrode.

A major challenge in the industrial use of enzymes is maintaining their stability at elevated temperatures and in harsh organic solvents. In order to address this issue, we investigated the use of nanotubes as a support material for the immobilization and stabilization of enzymes in this work. SnO₂ hollow nanotubes with a high surface area were synthesized by electrospinning the SnCl₂ precursor and polyvinylpyrrolidone (dissolved in dimethyl formamide and ethanol). The electrospun product was used for the covalent immobilization of enzymes such as lipase, horseradish peroxidase, and glucose oxidase. The use of SnO₂ hollow nanotubes as a support was promising for all immobilized enzymes, with lipase having the highest protein loading value of 217 mg/g, immobilization yield of 93%, and immobilization efficiency of 89%. The immobilized enzymes were fully characterized by various analytical methods. The covalently bonded lipase showed a half-life value of 4.5 h at 70 °C and retained ~91% of its original activity even after 10 repetitive cycles of use. Thus, the SnO₂ hollow nanotubes with their high surface area are promising as a support material for the immobilization of enzymes, leading to improved thermal stability and a higher residual activity of the immobilized enzyme under harsh solvent conditions, as compared to the free enzyme.