Impact of heterogeneous electrode design on vanadium redox flow batteries with different flow fields

With the rapid progress of processing technology, the heterogeneous optimization design of porous electrodes is becoming practicable. Nevertheless, there is currently a lack of understanding of the relevant theoretical foundation. In this study, we systematically examine the influence and mechanism of various carbon paper (CP) stacking schemes on the performance of vanadium redox flow batteries (VRFBs) with different flow fields (interdigitated flow field, IFF, and serpentine flow field, SFF) through experiments and simulations. We find that the optimization of porous electrode heterogenization shows significant differences. For the IFF, optimizing the porous electrode structure remarkably improves the mass transfer effect near the membrane, thus enhancing the performance of VRFBs. For the SFF, the effectiveness of electrode structure optimization is manifested mainly in the improvement of the permeability of the porous electrode. Furthermore, the effectiveness of the heterogeneous design of the porous electrode depends on a balanced relationship between the mass transfer rate of the reactants and the rate of the electrochemical reaction. The Damköhler number is introduced to measure this balance and serve as a basis for subsequent optimization.