Nano-functional Materials For Energy Conversion And Storage Devices

Nano-functional materials hold the key to fundamental developments in energy conversion and storage, both of which are essential to meet the challenge of global warming and the limited unrecyclable nature of fossil fuels. In this dissertation, we focus on the synthesis of nano-functional materials and their applications in dye-sensitized solar cells and rechargeable lithium-ion batteries.Dye-sensitized solar cells (DSSCs) have attracted extensive attention as a promising alternative to traditional silicon-based photovoltaic devices on account of their special features, such as high power conversion efficiency and low production cost. Nano-functional materials open a door to further enhance the power conversion efficiency (PCE) of DSSCs. Herein several efforts have been carried out to improve the PCE of devices via introducing new nano-functional materials in DSSCs:A bifunctional ZnO compact film (ZCF) has been introduced in DSSCs via a facile spin-coating method, which not only suppresses back electrons transfer from FTO to electrolyte but also blocks the electrons injection from the conduction band of TiO2to FTO. The former effect effectively reduces the recombination which occurs in the region of FTO substrate, and the latter leads to remarkable increment of electron density in the TiO2, thus resulting in enhanced Voc, FF, and PCE. Furthermore, this ZCF has been compared with conventional TiO2compact film (TCF), and their different influences to photoelectron conversion process and the performance of DSSCs have been systematically investigated. The device based on ZCF remarkably improves Voc and FF, finally increases PCE by13.1%compared to the device based on bare FTO and4.7%compared to the counterpart based on FTO/TCF.It is essential to design and fabricate a compatible structure of the photoanode, due to its important role of affecting dye loading, light scattering, and electron diffusion. A well interconnected hierarchical TiO2spheres (TSP) has been achieved and applied in DSSCs.The photoanode based on TSP has been constructed via the post-treatment of an organic colloid, which remarkably improves electron transport between constructed hierarchical TiO2spheres (C-TSP). In particular, we prepared an Au nanoparticles containing organic colloid (Au@organic colloid) to achieve plasmon-enhanced constructed TiO2spheres (PC-TSP), resulting in further enhancement of Jsc and PCE. The device based on PC-TSP gives the highest PCH of6.62%, which is an increase of17.4%compared to ISP and4.6%compared to C-TSP.Rechargeable lithium-ion batteries have been considered as prime candidates to power the next generation of plug-in hybrid electric and electric vehicles (P-HKVs and KVs), due to their high energy and power density. o achieve the goal that is essential to meet future challenges of energy storage, the design and fabrication of new materials, especially in the form of new nano-functional materials, is critical. In this dissertation, several efforts have been made to improve the cycling reversibility and rate performance of batteries via synthesizing nano-functional materials with variable structures:Ordered three-dimensional LiNi0.5Mn0.5O2nanostructures have been synthesized via an in-sile lithiation method using variable manganese oxide octahedral molecular sieves (OMS) as template. The battery based on ordered3D LiNi0.5Mn0.5O2nanostructures exhibits a remarkable enhancement of cycling reversibility and rate performance compared with that of LiNi0.5Mn0.5O2particles prepared by a conventional solid-state reaction method (SS-LiNi0.5Mn0.5O2). The battery based on LiNi0.5Mn0.5O2nanoarchitectured spheres (NS-LiNi0.5Mn0.5O2) retains a discharge capacity of153.5mAh g-1(93%of the first discharge capacity) after75cycles.A specific discharge capacity of121.9mAh g-1is retained at a rate of3.2C, which is about70%of the capacity at a rate of0.2C. The battery based on nanoarchitectured flowers (NF-LiNi0.5Mn0.5O2) retains a discharge capacity of151.6mAh g-1(93%of the first discharge capacity) after50cycles. A specific discharge capacity of141.8mAh g-1is retained at a rate of3.2C, which is about80%of the capacity at a rate of0.2CTo overcome the drawbacks of silicon anode, three-dimensional silver-embedded porous silicon micronparticlcs (3D Ag@porous silicon) have been synthesized by a facile and low cost method via a metal-assisted chemical etching process. The electrode based on this3D Ag@porous silicon anode material reveals a significant improvement in the electrochemical performance that results from its unique interconnected3D network structure and the existence of high conductive silver nanoparticles encapsulated in the matrix of porous silicon. The battery based on3D Ag@porous silicon micronparticles still retains a discharge capacity of784mAh g-1after50cycles, which is more than two times larger compared with that of graphite (～372mAh g-1).