Studying the influence of electrode height-to-width ratio for optimal overall efficiency in vanadium redox flow batteries

Abstract

Electrode configuration is one of the key factors affecting the performance of a Vanadium Redox Flow Battery (VRFB). Therefore, it should be carefully designed in accordance with the operating conditions to achieve optimal system efficiency. In this study, multiple electrode aspect ratios (A.R. = electrode height-to-width ratio) were investigated using a two-dimensional (2D) numerical model under a range of operating conditions. The overall battery performance was evaluated to identify the most efficient cell configuration in terms of the optimal electrolyte flow rate, maximum output power, and overall battery efficiency. The results indicate a substantial improvement in both energy and overall battery efficiencies for cell A.R.4 (largest aspect ratio) compared with cell A.R.1 (smallest aspect ratio). At a flow rate of 20 mL min⁻¹ and a current density of 45 mA cm⁻², the energy and overall battery efficiencies increased by 13.5% and 12.4%, respectively. At a higher current density of 75 mA cm⁻² under the same flow conditions, the improvements became more pronounced, reaching 18.8% for energy efficiency and 19.4% for overall battery efficiency. Overall, cell A.R.4 demonstrated the best electrochemical performance among all evaluated cells, achieving the highest energy and system efficiencies, whereas cell A.R.1 consistently exhibited the poorest performance. However, the relative advantage of A.R.4 over A.R.1 became less pronounced under low current density and/or high flow rate operating conditions. Furthermore, cell A.R.4 achieved its maximum overall battery efficiency at a comparatively lower optimal electrolyte flow rate, thereby mitigating electrolyte leakage and enhancing operational reliability.