Flow visualization in a vanadium redox flow battery electrode using planar laser induced fluorescence

In this research, the flow behavior through a commercial electrode used in Redox Flow Batteries (RFB) was characterized by means of Planar Laser Induced Fluoresce imaging (PLIF) for different cell configurations, without channels or with channels machined either in the back plate or in the electrode. Measurements of the pressure drop were obtained for each case, and the evolution of the electrode soaking process was quantified defining an electrode surface wetting rate. Using the pressure drop measurements, equivalent Darcy and intrinsic permeability coefficients were calculated for the different configurations. It was observed that the tight fitting of the electrode within its housing appears to be crucial for an adequate distribution of the electrolyte within the porous media. In general, when channels are available, the electrolyte tends to circulate along them, without crossing through the electrode felt, and lower pressure losses are accompanied by lower wetting rates. The flow field with serpentine channels in the back plate could be considered the most suitable configuration in terms of energy consumption, nearly 87% less than in a case without any channels, but this same percentage of electrolyte will exit the cell without traversing the electrode, and thus not contributing to the electrochemical reactions.