Abstract
Tremendous efforts have been made on the development of unique electrochemical capacitors or pseudocapacitors due to the overgrowing electrical energy demand. Here, the authors report a new and simple strategy for fabricating hybrid MnOx-coated ZnO nanorod arrays. First, the vertically aligned ZnO nanorods were prepared by chemical bath deposition (CBD) as a template providing a large surface area for active material deposition. The manganese oxide was subsequently coated onto the surface of the ZnO nanorods to form a hybrid MnOx-coated ZnO nanostructure by anodic deposition in a manganese acetate (MnA)-containing aqueous solution. The hybrid structure of MnOx-coated ZnO nanorod arrays exhibits a large surface area and high conductivity, essential for enhancing the faradaic processes across the interface and improving redox reactions at active MnOx sites. A certain concentration of the deposition solution was selected for the MnOx coating, which was studied as a function of deposition time. Cyclic voltammetry (CV) curves showed that the specific capacitance (SC) of the MnOx-coated ZnO nanostructure was 222 F/g for the deposition times at 10 s when the concentration of MnA solution was 0.25 M. The unique hybrid nanostructures also exhibit excellent cycling stability with >97.5% capacitance retention after 1200 CV cycles. The proposed simple and cost-effective method of fabricating hybrid nanostructures may pave the way for mass production of future intelligent and efficient electrochemical energy storage devices.
Highlights
Supercapacitors, called electrochemical capacitors, are indispensable energy storage devices that have recently attracted great research interest from both academia and industry because they are specified to be as important as batteries for future energy storage systems
The growth of the Zinc oxide (ZnO) nanostructure on the stainless-steel substrate by the chemical bath deposition (CBD) method generally depends on the deposition time, temperature and pH condition
The deposited ZnO nanostructure on stainless steel substrate as a function of various deposition time exhibited sharp and clear diffraction peaks, which are well indexed based on crystalline hexagonal wurtzite phase of ZnO (JCPDS card no.: 80-0075)
Summary
Supercapacitors, called electrochemical capacitors, are indispensable energy storage devices that have recently attracted great research interest from both academia and industry because they are specified to be as important as batteries for future energy storage systems. On the basis of their charge storage mechanisms, supercapacitors are generally classified into two main categories—electric double-layer capacitors (EDLCs) and pseudocapacitors [4,5]. EDLCs are composed of carbonaceous material such as activated carbon, carbon aerogel, etc., which have more specific surface area; unlike pseudocapacitors, which store electrical energy by the electrostatic accumulation of ionic charges in the electrical double-layer, nearby electrode, and electrolyte interfaces. Pseudocapacitors exhibit higher specific capacitance and energy density of more than 10 times as compared to EDLCs. the pseudocapacitor has been considered to be a promising device for applications of high power density and high energy density due to their relatively fast and reversible faradic redox reactions
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