Novel Obstructed Flow Field Designs for Improved Perfomance in Vanadium Redox Flow Batteries

Abstract

One of the major challenges that limits the widespread commercialization of vanadium redox flow batteries (VRFBs) is their relatively low power density, which often results in higher cost [1]. In recent years, significant effort has been put on understanding the effect of flow field design on the power density performance of VRFBs [2-3]. Flow fields play a crucial role in effective delivery and removal of active species from the electrode surface and hence they can significantly alter the power output of the VRFBs. Due to inherent similarities between fuel cells and redox flow batteries, flow field designs for VRFBs have been limited to previously studied conventional flow designs such as parallel, serpentine, and interdigitated. Though significant effort has been placed on analyzing which design performs better and how certain parameters can result in higher performance; investigation of novel flow designs outside the fuel cell research has remained much unexplored. Although conventionally utilized flow field designs have very different flow paths for delivery of the electrolyte in two dimensions; the channel depth seems to remain constant for the flow field studies reported so far. Considering the porous electrodes lie in parallel with the channel floors in most of the VRFB cell fixtures, it is believed that alterations of the channel depth throughout the length of the flow channels can help facilitate better transport of active species to the electrodes. Motivated by this, various forms of channel obstructions and ramped flow field designs have been investigated to understand the effect of channel depth and delivery of electrolytes on the power density of the VRFBs. Results have shown significant improvements in power density (up to 90%) with the addition of alterations to the channel depth with minor (10%) or no change in pumping losses. These findings suggests that engineering of the flow field designs in all three dimensions can help further improve the power density of VRFBs.