The adsorption properties, wetting ability and electrochemical impedance spectrum properties of graphite felts in vanadium electrolyte were investigated. The results show that adsorption property and wetting ability were increased with increasing the extent of oxidation. The alternating current impedance diagram consists of two semi circles and a line, in which the high frequency zone was ascribed to adsorption process within porous structure and the low frequency zone to the kinetic impedance of electrochemical reaction. The higher the extent of oxidation, the smaller the semi circle in the low frequency zone. The changes in the value of electrochemical impedance can be explained by the increase of COOH group on the graphite felt surfaces after electrochemical oxidation. The equivalent circuits of graphite felt electrode were proposed and the corresponding simulated kinetic parameters were also discussed.

Key words: vanadium redox cell, graphite felt, electrochemical oxidation, AC impedance, adsorption