Multiscale mechanisms and operational optimization of flow rate regulation in iron-chromium redox flow batteries

Iron-chromium flow batteries are emerging as a promising technology for large-scale energy storage, offering high safety and long cycle life. However, their performance is being strongly influenced by electrolyte flow rate: insufficient flow is exacerbating concentration polarization, while excessive flow is increasing pumping losses and reducing system efficiency. This study is establishing an integrated framework that is combining experimental characterization with three-dimensional multiphysics simulations. Specifically, an Fe 2+ /Fe 3+ symmetric cell test platform was constructed, and a numerical model coupling fluid dynamics, ion transport, and electrochemical kinetics was developed on a multiphysics platform. Using this framework, key physical parameters are being systematically analyzed under varying flow rates per unit electrode area, including flow characteristics, reactant concentration distribution, current density distribution, polarization behavior, and long-term cycling stability. Results show that an optimal flow rate of 1.5 mL/min/cm 2 is enhancing flow uniformity and reactant distribution, achieving a ∼13.06 % increase in concentration uniformity and 83 % voltage efficiency, while maintaining low pressure drop (1354.5 Pa) and pumping losses. These findings confirm 1.5 mL/min/cm 2 as the optimal balance between performance and energy cost, providing a valuable parameter reference for flow-field design and operational control of small-scale Fe-Cr flow batteries with similar configurations and fixed flow channel designs.