Investigation of a method to hinder charge imbalance in the vanadium redox flow battery

Abstract

In common with most aqueous batteries, the vanadium redox flow battery generates a small amount of hydrogen during operation. Over the lifetime of the battery this leads to a gradual imbalance in the state-of-charge (SoC) of the positive and negative electrolytes, with a consequent loss in discharge energy. To slow the rate of capacity fade to an acceptable level commercial vanadium redox flow batteries operate with a rather restricted maximum SoC. Increasing this SoC limit would improve the electrolyte utilisation, but also increase the rate of hydrogen evolution. Therefore a novel approach to alleviate this imbalance is examined, namely by reacting the evolved H2, from the parasitic reaction at the negative electrodes, with the charged positive electrolyte. Due to the very slow native rate of reaction between VO2+ and H2 at room temperature a series of potential catalysts are examined. Finely dispersed Pt, Ir and Pt–Ru on carbon paper are found to accelerate the reaction, with Pt–Ru being the most active.