Particle based method and X-ray computed tomography for pore-scale flow characterization in VRFB electrodes

Porous electrodes are pivotal components of Vanadium Redox Flow Batteries, which influence the power density, pressure drop losses, activation overpotentials, limit current density, bulk and contact resistance, and ohmic losses. The quantification of the fluid-mechanic efficiency of porous electrodes based on their real geometry is a useful measure, as it primarily affects the mass transport losses and the overall battery performances. Although several studies, both numerical and experimental, have been devoted to the electrode enhancement, most analyses are carried out under the simplifying assumption of linear, macrohomogeneous and isotropic behavior of the fluid mechanics in the porous material. We present an original approach built on the Lattice-Boltzmann Method and Lagrange Particle Tracking that makes use of pore-scale accurate geometrical data provided by X-ray computed tomography with the aim of studying the dispersion and reaction rates of liquid electrolyte reactants in the flow battery porous electrode. Following this methodology, we compare the fluid-dynamic performances provided by a commonly used carbon felt and an unconventional material, that is, a carbon vitrified foam. Surprisingly, results unveil the possibility of achieving higher fluidmechanic efficiencies with the foam electrode, whose intrinsic microstructure promotes higher reaction rate.