Coulometric analysis method for determining the concentration and degree of oxidation of vanadium in the electrolyte of a vanadium flow battery using a hydrogen vanadium cell

Determining the vanadium content and the average degree of oxidation of vanadium ions in an electrolyte is a highly important task, both in the production and operation of vanadium flow batteries and in scientific research aimed at improving the performance characteristics of electrolytes throughout their entire life cycle. This article proposes a solution to this issue using the coulometric analysis of electrolyte samples circulating through a cell with a membrane-electrode unit consisting of a gas diffusion hydrogen electrode, a proton exchange membrane, and a liquid flow electrode. The coulometric analysis involves the oxidation of the sample to the highest degree of vanadium oxidation with further reduction to an oxidation state of +4. The parameters of the procedure (polarization modes and completion conditions) were chosen in order to minimize the relative error in determining the concentration of vanadium up to 5% and the average degree of oxidation up to 2% based on model composition electrolytes with different concentrations and degrees of vanadium oxidation, including sulfuric acid, as well as mixed acid (H2SO4 + HCl) compositions