On the Role of Electrode Thickness in Redox Flow Cell Performance

The electrode thickness is a critical design parameter determining the overall flow cell performance through the available surface area for reactions, current and potential distributions, and required pumping power. To date, current redox flow cell assemblies employ repurposed off-the-shelf fibrous electrodes, yet a broad range of thicknesses have been reported, showing that the influence of the electrode thickness on the reactor performance is not well understood. Here, we investigate the effect of the electrode thickness in the range of 200 - 1100 µm on the cell performance by stacking electrode layers in four different flow cell configurations – paper and cloth electrodes combined with flow-through and interdigitated flow fields. We employ a suite of electrochemical and fluid dynamic diagnostics together with pore network modeling simulations to correlate the electrode thickness with the pressure drop and electrochemical performance. We find that for each electrode-flow field combination, there is a unique dependency to electrode thickness. Thicker electrodes are beneficial in combination with flow-through flow fields, whereas when using interdigitated flow fields, thinner electrodes are better suited for the electrochemical performance and pressure losses trade-off. We hope our findings will aid researchers and technology practicioners design their electrochemical flow cells under convective operation.