| All-vanadium redox flow battery is a new energy storage system developed quickly in recent years. It has some special properties such as high storage efficiency, long service life, environmental friendly, low price, and low costs of operation and maintenance. However, there are many factors influenced VRB performance. Among those factors, the performance of electrode materials and anode and cathode reaction plays an important role in VRB performance. In this paper, the electrode materials of VRB were modified, and the kinetic parameters of varies working electrodes reaction were also calculated. Achievements in this paper are listed as follows:1. The conductivity and the electrochemical properties of the conductive pastern doped different conductive fillers were studied. The results showed that the resistivity of 40% dilates graphite were lower compared with 40% graphite felt. The conductivity of conductive pastern doped dilates graphite and particulate graphite was improved. The electrochemical performance test showed that the oxygen evolution was difficult to occur due to the high oxygen evolution potential of 40% graphite felt.2. The redox reaction of V5+/V4+ couple in VOSO4 solution on various electrodes was studied by cyclic voltammetry and linear polarization method. The results showed that the couple had better redox reversibility, the conductive plastic electrode had broad water stable region, and hydrogen was likely to evolve on platinum electrode. The rate constant of V(IV) electrochemical reduction into V(III)was far less than V(IV) electrochemical oxidation into V(V). Therefore, the reduction peak of V4+/V3+ was not located in the cyclic voltammetry test. The kinetic parameters of oxidation reaction of V5+/V4+ couple on graphite, platinum, and conductive plastic plate were also calculated, and the exchange current density of the couple was 1.60×10-3 A·cm-2,2.541×10-5 A·cm-2, and 3.814×10-5 A·cm-2, respectively, and the exchange current density of the V4+/V3+ couple on conductive plastic plate was 3.235×10-6 A·cm-2.3. The diffusion coefficient of V(IV) in 1.0-2.5 mol·L-1 H2SO4+0.1-1.0 mol·L-1 VOSO4 which was obviously decreased from 1.58×10-3 to 2.03×10-4 cm·S-1 with increasing concentration of V(IV) was estimated by the cyclic voltammetry and chronoamperometry. However, the sulfuric acid concentration had little effect on diffusion coefficient of V(IV). The redox reaction of V5+/V4+ couple was an irreversible reaction controlled by diffusion. The oxidization rate can be accelerated by improving the concentration of V(IV), and the sulfuric acid concentration has no obvious effect on the oxidization of V(IV).4. Graphite felt was treated with potassium permanganate solution, and the effect of concentration and bath temperature on graphite felt performance was experimentally investigated. The results showed that the hydrophilicity was improved due to the appearance of surfactant group on the surface of graphite felt. The potassium permanganate deposited on graphite felt was unfavorable to the reaction of vanadium ions, however, the graphite felt treated with saturation potassium permanganate at 90℃bath could completely embody the vanadium ion valence changes, and improve the electrochemical performance of the graphite felt.5. SnO2 thin films on the surface of graphite felt was successfully deposited by chemical deposition and physical adsorption. Compared with chemical deposition, lesser SnO2 grain was adsorbed on the surface of graphite felt by physical adsorption, while uniform and well-knit SnO2 thin film can be obtained by chemical deposition. The results showed that the peak current and the duration time of oxidation of V3+/V2+ couple, V4+/V3+ couple, and V5+/V4+ couple enhanced after depositing SnO2, this indicated that SnO2 performs a catalytic action on the reaction of vanadium ions on the surface of the electrode, and both the hydrogen and the oxygen evolution overvoltage on the SnO2 modified electrode enhanced.6. The performances of inoperative battery after repeated charge-discharge cycles were studied. The results showed that both conductive plastic current collector plate of the anode and the graphite felt were corroded by oxygen corrosion, and the resistance of the plate increased due to the loss of carbon, while pitting corrosion was observed on the surface of carbon fiber. The oxygen atom evolving on cathode during charging process has strong oxidizability, and its reactivity with carbon is similar to the oxygen in 500℃air. The oxygen evolution on anode during the charging process of the cathode was studied and the reason of electrode corrosion was found. Hydrogen was evolved during the charging process of the cathode, and the-CH2 generated on the graphite felt.7. Nickel coating on the carbon-polythene composite plate was prepared by electrodeposition in a nickel sulphate solution, and the adhesion strength between the nickel coating and substrate can be more than 2.3 MPa. The growth of nickel coating could inherit some characteristics of the substrate geometrics, and therefore the coating roughness was strongly depended on the roughness of the composite plate substrate. The corrosion potential of the bright coating in the NaCl aqueous solution was more positive than that of the dull coating, and the anodic dissolving rate of the bright one was also far lower at the same polarization potential compared with the dull one. |
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