A numerical study of electrode thickness and porosity effects in all vanadium redox flow batteries

Abstract

Vanadium redox flow battery (VRFB) is one of the promising technologies suitable for large-scale energy storage in power grids due to high design flexibility, low maintenance cost and long-life cycle. Vanadium redox flow cell consists of two porous electrodes with serpentine flow channels and electrolyte solutions which is separated by an ion-exchange membrane. The temperature has been set to 298 K for the electrolytes which is composed of 1500 mol/m³ initial vanadium concentration with 4000 mol/m³ initial H2SO4 concentration. We developed a three-dimensional model to scrutinize the complexities of fluid dynamics and electrochemical reactions when considering different electrode thickness sizes, electrode porosity and electrolyte flow rates. In this study, a three-dimensional numerical simulation have been performed in order to investigate the effect of electrode thickness and electrode porosity on the performance of VRFB. The impact of electrolyte solution flow rate on the VRFB electrical characteristics and efficiencies are also numerically investigated. The results show that the cell voltage increases with increasing the electrolyte flow rate and electrode porosity during discharging process of VRFB. Increasing the initial vanadium concentration, the VRFB cell voltage is significantly increased due to reduced overpotential in the porous electrodes. The maximum power-based efficiency of 96.8% is calculated with the electrode thickness of 1 mm at 10 ml/min, while the power-based efficiency of 96.4% is calculated with the electrode thickness of 4 mm at 50 ml/min. This work gives comprehensive insights on electrode configurations for VRFBs.