In-situ measurements and experimentally-validated modeling of reaction kinetics in iron-chromium flow batteries

Understanding of the reaction kinetics of active redox couples on porous electrodes is essential for enhancing flow battery performance. However, most previous kinetics studies were conducted under ex-situ conditions using planar electrodes. As a result, the derived parameters do not accurately represent the kinetics on practical porous electrodes. Furthermore, research on iron‑chromium flow batteries (ICFBs) in the literature has been primarily experimental, with limited emphasis on cost-effective, practical modeling. This study proposes a novel in-situ method that uses a symmetric cell to evaluate the electrode kinetics of the Fe2+/Fe3+ and Cr2+/Cr3+ couples on porous electrodes. By first determining the ohmic polarization through high-frequency resistance measurements and subtracting it from the total polarization, we obtain the activation polarization curves for both couples under conditions of negligible concentration polarization. Subsequent Butler-Volmer fitting yields the reaction rate constants and charge transfer coefficients. Finally, the model constructed with these in-situ kinetic parameters is validated against full-cell experimental data, confirming their reliability and establishing a comprehensive modeling framework for ICFBs.