Valence Modification Of Vanadium Oxide And Energy Conversion And Energy Storage

In recent years, the environmental effects of greenhouse gases, energy security and the rising energy costs based on fossil fuel have been paid much attention. Herein, developing and utilizing renewable energy and energy storage lead the direction of scientific research once again. The energy conversion effect in the process of variations valences of vanadium gives the vanadium oxide catalysts many special properties, which stimulate interest of scientists. However, vanadium compounds with special valence are not stable in air, which causes much difficulties. Therefore, we try to synthesize stable low valence vanadium oxides and introduce impurity ions to improve their performances, and then study on their energy conversion performance. The main research contents in this thesis are as follows:1. Vanadium dioxide nanowires were synthesized via reducing commercial vanadium prentoxide powder. We use melamine and commercial vanadium prentoxide powder as raw materials, mixing them in aqueous solution to obtain precursor, and then calcining under protection of nitrogen to reduce the pentavalent vanadium ions. The vanadium dioxide nanowires we prepared have high crystallinity, stable chemical property, and display well performance on water splitting under ultraviolet light irradiation without noble metal co-catalyst supporting.2. Calcium vanadate with one-dimensional structure was synthesized via typical solvothermal method. Calcium acetate and ammonium metavanadate were utilized respectively as the source of calcium and vanadium, meanwhile, ethylene glycol was utilized as solvent and reducing agent in the synthesis process. Then solvothermal products were calcined under nitrogen protection to form the calcium vanadate nanorods. The material with 5 wt% RuO2 loading can produce oxygen in pure water under UV irradiation, which shows good performance.3. Urchin-like structure magnesium vanadate microspheres were synthesized via solvothermal method. Ethylene glycol dissolving magnesium acetate and ammonium metavanadate utilized as raw materials and played a role of reducer and structure directing agent in the solvothermal process, which reduced the +5 valence vanadium ion to low valent state and formed the urchin-like morphology. After calcination under protection of nitrogen, the morphology could be maintained. The material showed perfect performance as lithium ion battery anode.4. Yolk-shell structure vanadium sesquioxide microspheres were synthesized via solvothermal method. We use ammonium metavanadate and ethylene glycol as raw materials, in which ethylene glycol regarded as reducer and structure directing agent in the solvothermal process. The material utilizing as anode materials for lithium ion batteries showed excellent electrochemical stability and perfect specific capacity.