Numerical study of the effects of carbon felt electrode compression in all-vanadium redox flow batteries

• The effects of electrode compression on VRFB are examined.
• The electronic conductivity is improved when the compression is increased.
• The kinetic losses are similar regardless of the electrode compression level.
• The vanadium distribution is more uniform within highly compressed electrode.

The porous carbon felt electrode is one of the major components of all-vanadium redox flow batteries (VRFBs). These electrodes are necessarily compressed during stack assembly to prevent liquid electrolyte leakage and diminish the interfacial contact resistance among VRFB stack components. The porous structure and properties of carbon felt electrodes have a considerable influence on the electrochemical reactions, transport features, and cell performance. Thus, a numerical study was performed herein to investigate the effects of electrode compression on the charge and discharge behavior of VRFBs. A three-dimensional, transient VRFB model developed in a previous study was employed to simulate VRFBs under two degrees of electrode compression (10% vs. 20%). The effects of electrode compression were precisely evaluated by analysis of the solid/electrolyte potential profiles, transfer current density, and vanadium concentration distributions, as well as the overall charge and discharge performance. The model predictions highlight the beneficial impact of electrode compression; the electronic conductivity of the carbon felt electrode is the main parameter improved by electrode compression, leading to reduction in ohmic loss through the electrodes. In contrast, the kinetics of the redox reactions and transport of vanadium species are not significantly altered by the degree of electrode compression (10% to 20%).This study enhances the understanding of electrode compression effects and demonstrates that the present VRFB model is a valuable tool for determining the optimal design and compression of carbon felt electrodes in VRFBs.