The numerical study of vanadium redox flow battery performance with different electrode morphologies and electrolyte inflow patterns

Electrode morphological features and the electrolyte inflow pattern are important factors in determining the performance of vanadium redox flow batteries. In this study, a 2-D numerical model that couples electrolyte flow, ion diffusion, and electrochemical reaction is proposed to quantitatively investigate the mass transport and electrochemical reactions at various electrode structures, including the effects of porosity, fiber size, and fiber array pattern, as well as the electrode compression and the electrolyte inflow pattern. The influence of stochastic seeds on the reconstructed geometry was considered and assemble average value was conducted. The established model with the reconstructed geometry has been validated by experiment. The specific surface area, flow resistance, and VO₂⁺ consumption rate increase with a decreasing in electrode porosity and fiber diameter. The fiber array pattern with a “outlet dense and inlet sparse” structure shows the optimum performance of rapid VO₂⁺ consumption rate and high electrode utilization. The mass transport is dominated by convection in a wide flow path within the electrode, and the collective effects of convection and diffusion are found in a narrow flow path. The main advantage of the compressed electrode is the enhanced electrode utilization. A turning point at a stoich (the ratio of input reactant moles versus the consumed moles at a certain applied current) about 1000 was identified, below which the consumption rate of the flow-through pattern is higher than that of the flow field pattern and above which the consumption rate of the former pattern is slower than the latter. A faster fuel feed in the electrode with a narrower flow channel contributes to a faster species consumption rate in the last stage of the discharge process. The present study provides practical guidance for the design and optimization of VRFB electrode.