Photo Rechargeable Batteries

With the progress of society and rapid economic development, global energy demand is increasing rapidly. As the increasing gradually energy consumption and approaching depletion of traditional fossil fuel, energy shortage has become a bottleneck, which restricting the high speed development of human being society. Exploring alternative clean and renewable energy sources is the feasible way to meet the growing global energy demand. Solar energy has attracted considerable interest as potential low-cost, environmentally benign, abundant, and renewable alternative to conventional fossil sources. However, the intermittent nature of conventional solar cells has become a technological bottleneck for the effective utilization of solar energy. New type solar energy storage technique, which can solve the inconsistency of solar energy supply and demand, is needed to improve utilization efficiency of solar energy and conserve environment. In this thesis, a new kind of solar energy conversation and storage system, which is based on dye sensitized solar cell and rechargeable battery, is fabricated and investigated.Firstly, a solar rechargeable battery is fabricated with a dye sensitized TiO2photo-anode, TiN nanotube arrays/Ti mesh electrocatalytic electrode and WO3charge-storage electrode. TiN nanotube arrays on the metallic Ti mesh, prepared by a simple nitridation of TiO2nanotube arrays on the metallic Ti mesh in ammonia atmosphere, are introduced for the first time as low-cost electrocatalytic electrode for solar rechargeable battery. It is demonstrated from cyclic voltammetry (CV) and electrochemical impedance spectra (EIS) that the highly ordered TiN nanotube arrays on the metallic Ti mesh substrate show an excellent electrocatalytic activity. Correspondingly, the rechargeable battery with WO3as charge-storage electrode and TiN nanotube arrays/Ti mesh as electrocatalytic electrode presents reliable solar storable capability and reversible electrochemical conversion performance. In the dark, the discharge capacity of the battery with the TiN nanotube arrays/Ti mesh as the electrocatalytic electrode is about0.139mAh cm-2in the first cycle, when the cut-off voltage for discharging is set at0.2V at the current density of0.2mA cm-2 after photo-charging for30min under100mW cm-2irradiation. A discharge capacity of0.124mAh cm-2is still retained after10cycles, showing the good capacity retention. Therefore, the TiN nanotube arrays/Ti mesh prepared in this work can be used as a potential low-cost alternative to the expensive noble metal Pt in future applications of the solar storable rechargeable battery.Secondly, it is well known that solid-electrode batteries have too little energy to power ratio for the intermittent renewable energy storage, such as solar energy. A solar rechargeable battery based on Li2WO4/LiI couples in dual-phase electrolyte was proposed. The solar rechargeable battery is a type of reversible energy conversation and storage system which converts the solar energy to electrochemical energy while the electrolyte containing dissolved electroactive species is circulating through a redox flow cell. It is shown from the experiment results that the discharge capacity of solar rechargeable redox flow battery is about0.0153mAh mL-1in the first cycle, when the cut-off voltage for discharging is set at0.2V at the current density of0.075mA cm-2and a flow rate of0.05mL min-1after photo-charging for10min under100mW cm-2irradiation. A discharge capacity of0.0151mAh mL-1is still retained after10cycles, showing the good capacity retention. Theoretically, the electrochemical reaction and diffusion of the active species in liquid are much faster than that in solid. This feature would make the solar rechargeable battery unique in rate discharge capability in response to the power requirement. In this solar rechargeable battery system, the solar energy conversion and storage energy can be carried out in a redox flow cell, which offers a new way for the solar-generated electricity storage.Finally, the electrochemical performance of the electroactive organic compound quinoxaline and its derivatives employed as active species in anolyte for the solar rechargeable battery are investigated. Electroactive organic compound, which can be readily obtained from natural sources, have attracted increasing interest during the past few decades. In addition, the redox potential and electrochemical activity of Electroactive organic compound would be slightly varied when substituent groups and substituent sites are changed. The current study shows that the as-fabricated solar rechargeable battery using electroactive organic compounds as anode-active materials presents good solar rechargeable capability, subsequent discharge capability and cycle stability, indicating the feasible solar energy conversion and storage. It is shown from the experiment results that the discharge capacity of solar rechargeable battery is about0.0291mAh mL-1in the first cycle, when the cut-off voltage for discharging is set at0.2V at the current density of0.10mA cm-2and a flow rate of0.05mL min-1after photo-charging for10min under100mW cm-2irradiation. A discharge capacity of0.0207mAh mL-1is still retained after20cycles, showing the good capacity retention. Therefore, the organic compounds can be used as potential electroactive alternatives in anolyte for future applications of the solar rechargeable battery. Based on the working mechanism analysis and the experimental results, the electroactive organic species are successfully applied in solar rechargeable battery, offering a new path for the search, design and synthesis of novel materials with adjustable redox potentials and electrochemical activity. In addition, more attention should be focused on enhancing the long-term durability, raising the active material utilization and improving the energy conversion efficiency.In summary, three novel solar rechargeable batteries are proposed in this thesis based on dye sensitized solar cell and rechargeable battery. The strategy for designing energy system with dual function of solar energy conversion and storage provides a new direction for exploring new solar energy device.