In nanoscience research the morphology-controlled synthesis is a crucial issue to change and improve properties of materials at nanoscale. Among many methods, the solution-based chemical process has developed into a promising technique because it allows to easily tune morphologies with changing experimental parameters. To achieve different aspect ratios of NiO nanostructures, a NiCl2-Na2C2O4-H2O hydrothermal system with polyethylene glycol, ethylene glycol, and glycine as surfactant was suggested. However, their work was limited to form a nanowire bundle during the chemical reaction. Therefore, a solution system to obtain a wider range of morphological features of NiO needs to be developed. In addition to synthesis of NiO nanostructure, its coating to desired substrates is important. As a possible pathway, electrophoretic deposition (EPD) can be considered because of its high versatility and low cost equipment. EPD process can also be applied to various types of substrates such as fibers, cloths and complex shaped materials. Such a flexible, soft and nonfragile substrate has been explored for flexible and wearable functional devices.
In this study, nanostructured nickel oxide is synthesized using a hydrothermal method and tailored by triethanolamine. The structural properties of the nickel oxide particles were analyzed by using SEM and XRD. Strong dependence of the triethanolamine on NiO nanorods was found and their mechanism was investigated. For the fabrication of the devices, EPD of tailored nickel oxide was then used to construct nickel oxide electrodes on polyimide films for gas sensing measurements and carbon papers for electrochemical measurements. The morphology-controlled gas sensing properties of NiO were investigated with VOC gases. The performance of NiO for gas sensors were evaluated in terms of sensitivity and selectivity. The mechanism of p-type NiO for gas sensors is discussed in details. For nickel oxide catalysts, the urea electrooxidation in alkali medium were investigated and evaluated by cyclic voltammetry and chronoamperometry. In order to improve electrocatalytic activities, nickel oxide decorated by nickel and cobalt composite structures were also investigated.
The work was partially supported by the KIET Evaluation and Planning (20158520000210) grant funded by the Korea Government Ministry of Trade, Industry and Energy and Agency for Defense Development (ADD) as global cooperative research for high performance and light weight bio-urine based fuel cell (UD160050BD).