Numerical investigation on the dispersion effect in vanadium redox flow battery

The vanadium redox flow battery (VRFB) is a promising energy-storage technology for the power supply from intermittent renewable energy sources. An understanding of the characteristics of coupled mass transport and electrochemical reactions in a VRFB is of great importance for increasing the storage capacity and improving the efficiency. However, the dispersion effect in the porous electrode of VRFBs has been ignored in existing modelings. This paper reports on an reactive transport model considering dispersion effect for VRFBs, and the model is developed based on a comprehensive description of mass, charge, and momentum transport and conservation in porous electrodes and combined with a kinetic model for electrochemical reactions. In particular, considering the influences of dispersion on the reactive transport behaviors, the effective diffusivities of ions and the local mass transfer coefficient are accurately determined by experiments wherein the dispersion effect included. A good agreement is demonstrated between the simulated cell performance and experimental data over the full range of the state of charge (SOC). Compared with the results resolved from using the effective diffusivity as Bruggemann correction, the cell voltages have little discrepancies while the distributions of vanadium ions concentrations and local current density show obvious differences. The model is then employed to analyze the performance characteristics of VRFBs and to investigate the effects of various operating conditions and structural parameters on the cell performance and system efficiency. The numerical results allow us to identify the key areas of potential improvements to the storage capacity and efficiency of VRFBs.