Impurity Effects in All-Vanadium Redox Flow Batteries

In this dissertation, the effects of VOSO₄ [vanadyl sulfate] source and impurities on the beginning-of-life (BOL) performance of an all-vanadium redox flow battery (VRFB) are explored. Battery performance was monitored at 50% state of charge (SOC) using electrolyte with VOSO₄ purities of 99%, 99.9% and 99.99% by weight. At cell potentials of 1.23V, the least pure solution yielded the lowest current density of 280 mA/cm² [square centimeter] and the most pure solution yielded the highest, 560 mA/cm². The voltage efficiencies and charge-discharge capacities were shown to follow the same trends. Scanning electron microscopy (SEM) images revealed significant coverage of the electrode surface with deposited material, identified as Si. Blockage of electrode pores is proposed to be the primary reason for the BOL performance variation of the three suppliers tested. Filtration of low-purity electrolyte before testing was shown to remove the impurities, resulting in performance similar to high-purity electrolyte Further testing explored the effects of adding 1% iron by weight in the form of ferric sulfate as an impurity.