RfbFoam: An open-source framework for porous electrode modeling in redox flow batteries

Redox flow batteries (RFBs) are promising candidates for large-scale, stationary energy storage. However, their widespread adoption is limited by high costs and suboptimal performance, much of which is governed by the interplay between electrode properties and flow field design. These components control electrochemical reactions, mass transport, and hydraulic losses, making their coupled analysis essential for performance optimization and rational design. In this study, we present RfbFoam, an opensource software tool for simulating the coupled hydrodynamic and electrochemical transport phenomena in RFB half-cells at the continuum scale. Developed in OpenFOAM, the solver captures three-dimensional transport of momentum, species, and charge while incorporating Butler-Volmer kinetics and porosity-dependent transport properties. The flexible framework enables testing of various electrode-flow field configurations, with initial implementations modeling flow-through and interdigitated flow fields combined with porous electrodes. Model verification is performed through direct comparison with COMSOL Multiphysics, demonstrating excellent agreement in predicting polarization curves. Experimental validation using an iron symmetric RFB cell with electrodes prepared with non-solvent induced phase separation shows accurate reproduction of both electrochemical performance and pressure drop characteristics across multiple flow rates. The software enables detailed three-dimensional visualization of velocity, concentration, and current density fields, revealing transport limitations and electrode underutilization patterns inaccessible through experimental methods. This validated tool provides a foundation for further studies such as flow field design modifications and topology optimization for improved battery efficiency.