Spatially Resolved Analysis of an Organic Alkaline RFB to Investigate the Influence of the Operating Conditions

Abstract

Designing competitive and reliable Redox Flow Batteries (RFBs) requires the development of specific analytical tools at lab-scale. Specifically, the influence of the cycling conditions on the system performance must be well identified. An instrumented test bench dedicated to the tuning of the operating parameters and the monitoring of the battery internal behavior was developed. The use of a segmented cell with a 1D-like design allowed to focus on the local current distribution along the electrolyte flow. The study started by examining the performances of a RFB coupling the ferri/ferrocyanide couple (Fe(CN)6 3-/ Fe(CN)6 4-) to the anthraquinone Alizarin Red S, over 300 cycles. Once cycling in standard conditions was reviewed, a parameter study was performed to scan a varied range of operating points, by changing the current density, the flow rate and the temperature successively. Thanks to the spatially-resolved analysis of the cell, the global performance could be related to local processes. This investigation gave unprecedented insight of the internal operation of a RFB, with peculiar features appearing at the start of the charge and the discharge. It was shown that a same global response of the cell could actually hide very different internal operations.