| "2009United nations Climate change conference", commonly known as "Copenhagen Summit", was held at the Copenhagen, Denmark, In this meeting the protect of environment has become the most important topic. As we known energy is one of the most important materials of national economy and of our daily life. Thus, the energy storage technologies have attracted much attention with the utilization of wind energy, solar energy. Since the vanadium redox flow cell has been proposed by skyllas-kazacos and co-workers in1985this battery has attracted great interest of researcher all over the world such as Japan, Canada, Britain, China and other countries. Recently, Mitsubishi and Sumitomo Electric Industries have made great progress. since2001several demonstration plants have been operated in Japan. However, the work about the preparation of vanadium solution, mechanism of electrode reactions, and the development of novel vanadium need further research and development.Two methods were used to preparation of vanadium solutions.1) The vanadium solution was prepared by heating the mixture of vanadium trioxide and vanadium pentoxide in sulfuric acid solution, which utilized the autocatalytic effect of vanadium with mixed valence, to intensify the dissolving of the mixture of vanadium trioxide and vanadium pentoxide. The formations of vanadium ions were theoretically determined. Moreover, negative ΔrGm and ΔrHm of the reactions were calculated by thermomechanical analysis. The reactions was proved to be a spontaneous process (ΔrGm<0). The results were confirmed by the UV-Vis analysis for the formation of ions. Its electrochemical performance was characterized by cyclic voltammetry and charge-discharge. The results showed that the prepared vanadium solution had an excellent electrochemical behavior, which indicated that the method was suitable for the industrial application and. Our work may serve as the theoretical bases for industrial production of the electrolyte of vanadium redox-flow batteries.2) The vanadium solution was prepared by the mixture of hydrogen peroxide and vanadium pentoxide in sulphuric acid solution. The solubility mechanism of vanadium pentoxide was investigated. The valence and concentration change of vanadium solution were characterized by UV-Vis and ICP measurement in the following electrolysis procedure. ΔH and ΔGî–µf the reaction were calculated. The results showed that the reaction was exothermic. The electrochemical activity was characterized by the charging and discharging experiment. And the results showed that the high current efficiency, voltage efficiency, and energy efficiency of93.6%,98.1%and91.9%were obtained at the current density of2.4mA cm-2, respectively. This indicated that the prepared vanadium solution was suitable for vanadium redox-flow battery.An efficient, highly selective, fast (which only costs about two minutes per sample) andcost-effective spectrophotometric method for simultaneous determination of vanadium ions in different valence states has been successfully developed, especially for the mixed V(â…¢)/V(â…£) and V(â…¡)/V(â…¢) solutions in vanadium redox-flow battery. The result showed that the method presents the excellent linear relationship in determining the single system of vanadium electrolyte in its measurement scope. In the mixed V(â…¡)/V(â…¢) and V(â…¢)/V(â…£) systems, multi-wavelength method is attempted for simultaneous determination. And K-matrix is introduced into calculating. The concentration linear equations of vanadium ions in different valence states have been deduced. The experimental data of the method is compared with Chinese Standard Method. The result indicates that the low relative standard deviation (less than5%) is able to validate the precision and accuracy of our proposed new method.Carbon paper (CP) electrode was characterized in terms of kinetics of VO2+/VO2+and V3+/V2+couples for the vanadium redox-flow battery, the standard rate constants k of the two redox couples. The determined k values on CP of3.60×10-4cm s-1and1.44×10-3cm s-1for VO2+â†'VO2+and V3+â†'V2+, respectively, showed a remarkable increase by one or two order(s) of magnitude compared with c plane of pyrolytic graphite (c-PG) and glassy carbon (GC). The acceleration of the redox kinetics of vanadium ions is anticipated from the enhancement of surface area on CP, whereas the suppression of the kinetics was observed for ferricianate/ferrocianate system. The involvement of the inner-sphere reaction on the surface of the CP was suggested. These kinetic feature of CP against vanadium redox reactions shows that the CP is suitable for electrodes in the vanadium redox-flow battery.The energy efficiency of the redox-flow battery has not been investigated theoretically in terms of dependences on electrochemical factors. Parameters such as an electrode area, current density, and vanadium concentration were varied and the current efficiency, voltage efficiency, and energy efficiency were compared with the theoretical values. By impedance measurements, the voltage loss was divided into internal resistance and overvoltage components, and the overvoltage component provided by the charge and discharge experiments were confirmed to the corresponding components calculated by the Butler-Volmer equation. The comparison between the surface areas determined by the BET method and by the Butler-Volmer equation indicates that only0.14%of the surface site functions as the surface for the heterogeneous reaction of vanadium redox reactionSince the vanadium redox flow battery has a low energy density of25～35kW kg-1, this paper proposed a novel vanadium solid battery which employs a VOSO4/(VO2)2SO4solid in the positive half-cell electrolyte, and a V2(SO4)/VSO4solid in the negative half-cell electrolyte. An overall cell potential of approximately1.5V is expected for the vanadium solid battery, the average energy efficiency (ηEE) of94%at a current density of2and5mA cm-2has obtained. which is about10%higher than that of an all-vanadium battery, and the average energy density of56.20and62.90Wh kg-1were achieved at a current density of2and5mA cm-2, respectively, which is more than2.5times of the conventional vanadium redox-flow battery. The preliminary exploration shows that the vanadium solid battery is promising for hybrid vehicle. |
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