Driven by the increasing energy crisis and environmental pollution, the renewable energy is in an urgent need to replace the traditional fossil fuels. Serving as the energy transfer station, electrochemical energy storage devices, such as batteries and supercapacitors, are capable to convert the electricity produced by solar radiation, waves, and wind into electrochemical energy, and release such energy elsewhere. Therefore, these electrochemical energy storage devices can compensate the intermittency of renewable energy sources. Especially, supercapacitors possess the appealing features such as higher specific power, faster charging/discharging rate and much longer cyclic lifetime than rechargeable batteries, thus offering possibilities in a broad range of energy-related applications s...[ Read more ]

Driven by the increasing energy crisis and environmental pollution, the renewable energy is in an urgent need to replace the traditional fossil fuels. Serving as the energy transfer station, electrochemical energy storage devices, such as batteries and supercapacitors, are capable to convert the electricity produced by solar radiation, waves, and wind into electrochemical energy, and release such energy elsewhere. Therefore, these electrochemical energy storage devices can compensate the intermittency of renewable energy sources. Especially, supercapacitors possess the appealing features such as higher specific power, faster charging/discharging rate and much longer cyclic lifetime than rechargeable batteries, thus offering possibilities in a broad range of energy-related applications such as regenerative breaks in electric vehicles, memory back-up systems, etc. For the decades, extensive research have shown that nanostructured architectures have large surface-to-volume ratio, which could be the promising candidates to serve as the scaffold for high performance supercapacitors fabrication. In particular, three-dimensional (3-D) nanostructured pseudocapacitors have been targeted as the promising energy storage devices due to their large surface/interface area, efficient ion diffusion and electron transport pathway. As a result, pseudocapacitor electrodes fabricated based on 3-D nanowires (NWs), nanotubes (NTs), nanopillars (NPLs), etc., have been broadly explored. However, they are still far from the ideal architectures mainly because they are either fabricated into small aspect ratio 3-D electrodes, which possess low specific capacitance, or they have serve performance degradation due to the unstable structural property. Furthermore, the fabrication process of these 3-D architectures always involves costly lithographic and etching processes, which limited their practical applications and capability for mass production.

In this thesis, several 3-D architectures are successfully fabricated with cost-effective method, all are set to solve the above issues. Firstly, the free-standing 3-D gold (Au) nanospikes (NSPs) film was fabricated, and such film is highly flexible and transferable to arbitrary type of flexible substrate to enable applications that require high flexibility. The large surface area of NSPs is utilized to achieve high areal capacitance after deposition of thin layer of MnO₂ on both sides of the NSPs. Secondly, the high aspect ratio and mechanical stable 3-D fluorine doped tin oxide (FTO) nanopores (NPs) architecture was achieved via cost-effective ultrasonic spray pyrolysis (USP) method. The unique hierarchical MnO₂/FTO/AAO NPs (MFANPs) pseudocapacitor electrode based on FTO NPs arrays achieves both high areal and volumetric capacitance, together with a remarkable capacitance enhancement in comparison to planar electrode. Thirdly, a unique 3-D interconnected nanoporous (INPOS) architecture was fabricated via soft anodization of aluminum alloy. Such structure inherits all the structural merits of 3-D NPs, including large surface area, efficient electron transport, as well as good structural stability, while superior to 3-D NPs in higher porosity and better ion accessibility. Benefiting from the above superiority, the pseudocapacitor electrode built based on 3-D INPOS architecture achieves both high areal and volumetric capacitance, More interestingly, the unique 3-D interconnected structure promotes the electrolyte ions diffusion, thus 3-D INPOS electrode exhibits largely enhanced rate capability as compared with 3-D NPs electrode.