Introducing an Experimental Route to Identify and Unify Lab-Scale Redox-Flow Battery Cell Performances via Molar Fluxes and Cell Constants.

Redox flow batteries (RFBs) are a promising technology for grid energy storage based on their high potential for scalability, design flexibility, high efficiency, and long durability, hence great effort has been invested in this area of research. However, due to the large differences in lab-scale RFB cell design and construction as well their operational performance, fundamental studies on innovative RFB components (e.g., active materials, separators, additives) compare poorly due to the lack of standard setups, settings, and procedures. This work introduces an experimental calibration route for aqueous as well as nonaqueous RFBs based on a simple mass transport model using molar fluxes, enabling one to compare dissimilar lab-scale RFB cell setups by introducing several RFB parameters: First, K1, which summarizes the operating parameters of an RFB to identify the critical ratio (K1_critical) needed for efficient charge-discharge cycling using a simple overvoltage and charge efficiency evaluation; second, the RFB cell constant ζ, quantifying the influence of a lab-scale RFB setup on its performance; and finally, K2, ultimately enabling full comparison of (idealized) K1_critical operating parameters across RFB cell setups.