Steady-state amperometry as an online state of charge monitoring method for vanadium redox flow batteries

Abstract

For an efficient operation and extended lifetime of the VRFB (vanadium redox flow battery), monitoring of the state of charge (SOC) is essential. However, accurate methods that can be implemented in industrial systems are rare. This work represents the next step in developing a reliable, cost-effective and long-term stable monitoring system based on amperometric measurements, which enables the distinct determination of the SOC for the negative and the positive half-cell during operation of a VRFB. Steady-state amperometry is applied using custom-made flow-through cells with a single, standard disk working electrode in both electrolytes of a VRFB. The influence of electrode configuration, flow rate, and polarisation potential was evaluated. While an expected correlation between the measured currents and the SOC was evident, SOC-dependent deviations from the ideal theoretical equations were observed. With regard to this, a non-linear fitting model is derived from simple assumptions and its excellent agreement with the experimental data is used to explain the main cause for the aforementioned deviation.