Performance enhancement of vanadium redox flow battery by flow field modification: Channel height reduction and channel blockage

Abstract

Vanadium redox flow batteries (VRFBs) are one of the most promising energy storage devices, but they have not yet reached their viable pinnacle of performance and commercialization. A major hurdle has been low power density due to high concentration overpotential, which is a result of uneven electrolyte distribution. Improving the convective mass transfer by flow field modifications appears to be the key to tackling this challenge. In the present study, a 3-D half-cell model of a VRFB with a serpentine flow field is developed and simulated during discharge. Having chosen the average value and uniformity index of velocity magnitude in the electrode as indicators of convective mass transport, net power density is then compared for the modified flow fields, taking both required pumping power and discharge power into account. The new flow fields are designed based on two different methods: (i) reducing the channel height or (ii) adding an array of blocks with different heights in serpentine bends and channel midpoints. It is found that the best design among the investigated cases is the flow field with 100 % blockage at bends and 80 % blockage at channel midpoints. This design achieved the highest uniformity of electrolyte velocity in the electrode and more than 56 % enhancement in the net power density, reaching 276 mW cm⁻². The results of the present study can provide applicable insights for devising convenient flow fields and compact VRFB systems.