Short Flow-Through Length in Redox Flow Battery Electrodes Enhances Performance Characteristics

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Menne, Valentina ; Oswald, Kieran ; van der Heijden, Maxime ; Greese, Tobias ; Solovov, Timofei ; Zeyer, Klaus Peter ; Roth, Christina:
Short Flow-Through Length in Redox Flow Battery Electrodes Enhances Performance Characteristics.
In: Journal of the Electrochemical Society. Bd. 173 (2026) Heft 13 . - 133503.
ISSN 1945-7111
DOI: https://doi.org/10.1149/1945-7111/ae7cbd

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Abstract

This study investigates the influence of flow-through electrode length in redox flow batteries on mass transport and related changes in battery resistance and performance metrics. A modular test cell was used that accommodated electrodes between 3 to 20 cm long. Experiments were carried out at 10 and 50 state of charge and with different electrolyte velocities. Parasitic effects such as varying pumping power and inductive distortions were accounted for, enabling fair comparison of electrochemical results. Electrochemical impedance spectroscopy and pulse tests revealed that for the 20 cm electrode, mass transport can be responsible for over 50 of total cell resistance even with a low current density, and that its influence increases for higher currents and lower velocities. By reducing the electrode length to 3 cm, this value decreased to less than 12 for the same operating conditions. Polarization curves and cycling tests demonstrated the resulting impact on system performance, specifically reaching 30 more discharge capacity, higher discharge current densities up to 560 mA cm−2, as well as a threefold increase in maximum discharge power density. As commercially available graphite felts were employed, this study suggests a scalable path to high-power flow-through redox flow stacks.