Determination of the Ion Concentrations in VRFB by Non-Invasive Optical Techniques Due to Chemical Reactions, Complexes, and Side Reactions

Abstract

The vanadium redox flow battery has been intensively examined since the 1970s, with researchers looking at its electrochemical time varying electrolyte concentration time variation (both tank and cells, for negative and positive half cells), its thermal time variation, and the fluid flow behavior. Chemistry behavior of the electrolyte ions have also been intensively examined too. Our focus here was to examine the disturbance and effect of other chemical reactions and constituents to those typically found in the positive electrode electrolyte, while handling the less problematic negative electrode. Appropriate formulas are developed which allow assessment of the size of the effect, and their evaluation indicates something on the order of up to 14%. Therefore, for unambiguous non-invasive optical measurements, knowledge of the disturbance effect, and taking it into account will allow proper concentration determination. This treatment includes a comprehensive examination of identified side reactions which occur due to crossover ions between the electrodes.