Impact of Porous Microstructure on Performance of Redox Flow Batteries: A Modeling Study

Abstract

Electrodes are essential components of redox flow batteries (RFBs) that determine performance. Given the advances in 3D printing technologies, bottom-up design and manufacturing electrodes with controllable and reproducible properties can be attainable. In this study, pore network modeling is utilized to understand the coupled transport and reaction processes in Hydrogen-Bromine (H2/Br2) flow batteries. This study highlights the importance of the microstructure while designing a 3D printable microstructure. The 3D pore-scale model is validated against the experimental measurements using an unstructured pore network, extracted from a tomography scan of a commercial carbon paper. A printable ordered cubic lattice with the same permeability as carbon paper increases the maximum power density by 35% due to lower tortuosity and higher mass transport. A parametric study is carried out to understand the role of microstructure, such as pore size, throat size, anisotropy, and lattice unit size, for flow-through and interdigitated flow fields. It is shown that a smaller lattice unit, increases the reactive surface area, lowers the activation and mass transport overpotentials, and consequently enhances the performance of the battery. An improved microstructure design for both flow fields is proposed that intensifies the performance of the battery via engineering the flow path of the electrolyte.