Kinetic characterization of carbon felt electrodes for vanadium redox-flow batteries
The vanadium redox-flow battery (VRFB) is a promising stationary energy storage system, especially due to its long life and low hazard potential. During operation, the liquid vanadium electrolyte is pumped through porous carbon electrodes where reduction and oxidation reactions take place. The kinetics of this reaction significantly determine the performance of the battery, therefore different approaches to activate the felts are known, e.g. by thermal or electrochemical treatment. However, there is a lack of meaningful studies on the kinetics of vanadium ion reactions on porous electrode felts. The low conductivity of the electrolyte can lead to an inhomogeneous current density distribution within the electrode, which can falsify the results significantly.
Therefore, methods to determine the kinetics correctly even in porous electrodes should be developed . For this purpose, kinetic parameters (rate constant, reaction order) are to be determined experimentally on individual carbon fibers, first. These can then be used to describe porous carbon felts by means of models and thus provide a better understanding of the electrode processes. Moreover, this understanding helps to further increase the electrochemical activity and as a result, to improve the battery performance.