An analytical model for parametric study on serpentine and interdigitated flow fields in redox flow batteries

Flow fields can enhance the peak power density of redox flow batteries through distributing the electrolyte and thus reactants uniformly in the porous electrode. However, due to the distinct mechanisms of serpentine and interdigitated flow fields for mass transfer enhancement, the effectiveness of different flow fields is highly dependent on design and operating parameters of the flow cell, such as electrode material, channel's dimension, applied flow rate, and applied current density. The significant computational costs induced by the 3-D or 2-D numerical model on the one hand, and the demand for a deep understanding with respect to the effects of the different flow fields on the flow cell under varying geometric and operating conditions on the other hand, call for an analytical approach. Therefore, the present study establishes an analytical model for quantifying the mass transfer and the electrochemical overpotentials in the flow cell with the serpentine or the interdigitated flow fields. The validity of the analytical model is confirmed by comparisons with experimental and 3-D numerical simulation results under varying electrode materials and channel dimensions. Parametric study results show that the properties changes affect the flow cell implemented with different flow fields paradoxically. First, for the flow cell utilizing electrodes corresponding to a relatively high specific surface area and a low permeability, the interdigitated flow field is more worthy of recommendation, while as the permeability of the electrodes increases, the serpentine flow field becomes more competitive. Second, widening channel's and rib's widths is an effective approach to decrease the concentration overpotential for the interdigitated flow field, while its effects on that with the serpentine flow field is opposite. These results are expected to provide a valuable guidance for the application of interdigitated and serpentine flow fields in flow cells.