Development of innovative flow fields in a vanadium redox flow battery: Design of channel obstructions with the aid of 3D computational fluid dynamic model and experimental validation through locally-resolved polarization curves

Distribution of the electrolyte over the porous electrode is a critical issue limiting the power density of vanadium redox flow batteries. The flow field design involves a trade-off among high battery performance, low pressure drops, reduced electrolyte imbalance and thus the understanding of the physical phenomena regulating mass transport of the electrolyte is crucial to develop improved flow fields. This work firstly presents the development of a 3D computational fluid dynamic model that couples fluid dynamic analysis of the electrolyte with the electrochemistry of the reactions involved. The model simulates the influence of both single serpentine and interdigitated flow field. After extensive validation with respect to local polarization curves in symmetric cell with both positive and negative electrolyte, the model is used to design flow fields with two different channel obstructions: the first one is located at the channel wall, while the second one is placed close to electrode interface. Both obstructions create a localized pressure difference between adjacent channels, enhancing electrolyte permeation through porous electrode. Finally, model predictions are verified experimentally: considering cycling operation at different operating current densities, the second obstruction is more effective in obtaining a good trade-off among performance, pressure drops and evolution of exchanged capacity.