Heterostructured Redox-Based Nanomaterials for Supercapacitor Application

• Main Author: Afriyanti Sumboja
• Other Authors: Lee Pooi See
• Format: Theses and Dissertations
• Language: English
• Published: 2014
• Subjects: DRNTU::Engineering::Materials::Nanostructured materials; DRNTU::Engineering::Materials; DRNTU::Engineering::Materials::Energy materials
• Online Access: http://hdl.handle.net/10356/55447
• Institution: Nanyang Technological University

Nanomaterials for energy storage application play an important role in versatile and reliable use of energy, including the pressing requirement on clean energy resources. Huge proliferation of portable electronic devices and intermittent nature of renewable energy generations demand for an efficient and sustainable energy storage device. At the same time, energy storage devices are expected to store extraordinary amount of energy within small area of footprint while delivering the energy rapidly. Hence, revolutionary advances in structural design and material selection for high performance energy storage device are necessary in order to meet this challenging requirement. Supercapacitor is an energy storage device that is able to balance the need of high power density of capacitor and large energy density of battery. Pseudocapacitor which is based on redox materials is of interest due to its fast and reversible faradaic charge storage process, leading to the high capacitance of supercapacitor. Nanostructuring has been explored to increase the capacitance of electrode materials. However, as some of the intrinsic properties of the materials cannot be tailored easily by nanostructuring method, single phase nanostructured material may not always yield an optimum capacitance. In this thesis, integrating two or more materials to form heterostructured nanomaterials was adopted to overcome the limitation of single phase nanomaterials on meeting the criteria of large capacitance, good cycling stability and high rate capability. Three strategies were proposed in designing high performance heterostructured nanomaterial. First, shell material of coaxial nanowire structure has provided additional redox reaction and prevented the dissolution of core material into electrolyte, resulting in the high capacitance and outstanding cycling stability of supercapacitor electrode. Second, nanostructured current collector has enhanced both ions and electrons transport on wide accessible surface area of electrode material and provided mechanical support for electrode material, leading to the excellent rate capability, high capacitance and good cycling stability of supercapacitor electrode. Third, free-standing electrode has reduced the contact resistance and poor adhesion at electrode material/current collector interface by eliminating the need of current collector, yielding the high capacitance and good cycling stability of supercapacitor electrode. In addition, its flexible paper-like nature and high mechanical property was promising for its application in flexible supercapacitor device. Furthermore, localized and in-situ electrochemical characterization at micron/nano level was of interest to further advance the performance of supercapacitor electrode. In this thesis, Scanning Electrochemical Microscopy (SECM) was introduced as a promising technique to probe the kinetics of localized interfacial processes with high spatial resolution and accuracy. SECM study was focused on SECM feedback mode, in particular approach curve measurement to extract heterogeneous charge transfer rate constant and illustration of SECM tip and substrate voltammetry. SECM feedback mode measurements on porous nanostructure and thin film redox-based electrodes have shown favourable behaviour as facile charge transfer medium with low kinetics barrier property. This study has provided an insight to the relationship among the capacitive behaviour, physical and kinetics properties of electrode material. The work presented has provided significant contribution on synthesis, design approach and kinetics study of redox-based supercapacitor electrode. Furthermore, it has given enlightenment on fundamental understanding and advancement to optimize capacitive performance of supercapacitor electrode, for the benefit of an excellent supercapacitor device.