(47b) Graphite Felt Electrodes for Vanadium Redox Flow Battery: Long-Term Stability and Hydrogen Evolution Reaction

Vanadium redox flow battery (VRFB) represents a promising electrochemical energy storage solution for various applications and scales ranging from few-kW residential batteries to hundreds-MW grid stabilization sites. For further commercialization of the technology, the intensification of the reactions on porous electrodes is required. Intensification is often achieved by thermal treatment or catalyst deposition. Long-term stability of catalytic activity of thermally treated felt is very important for desired battery life time of more than 10 years. In this contribution, we carefully analyze the effect of the electrode potential and battery cycling on felt stability. Various felt types were characterized by a complex set of physico- (BET, XPS, Raman, SEM) and electro-chemical (CV, EIS) techniques and the effect of felt degradation on the battery performance and hydrogen evolution reaction was systematically evaluated. Labscale single-cell with inner platinum sense electrodes was modified to specifically test the felt at studied electrode potentials and also to characterize the performance of positive and negative electrode separately. The labscale battery system was modified to allow quantification of hydrogen evolution side reaction. The slow continual deactivation of negative electrode under long-term battery operation was found to be dependent on active surface area.