Stacked carbon paper electrodes with pseudo-channel effect to improve flow characteristics of electrolyte in vanadium redox flow batteries

Abstract

Recently, carbon papers (CPs) have attracted much attention as alternative electrode materials for vanadium redox flow batteries (VRFBs) because of large redox reaction sites owing to their high fiber volume fraction compared with the conventional electrode material, carbon felts (CFs). However, the low permeability of CPs in the in-plane direction tends to cause the side flow of electrolytes around the electrode, which in turn leads to an uneven flow of electrolytes. Therefore, until now, CPs have been applied only to flow-by type VRFBs. In this study, a method is developed to enhance the performance of CP electrodes with a pseudo-channel effect by means of holey patterns of the CP to apply flow-through type VRFBs. The electrolyte flow characteristics and electrochemical properties are analyzed through numerical simulations and cyclic voltammetry tests, respectively. The performances of the electrodes are analyzed through VRFB single-cell tests. As a result of numerical analysis, it is confirmed that the overall flow rate inside the electrode increases substantially, and the flow distribution becomes uniform owing to the pseudo-channel effect, which leads to an increase in efficiency. At a current density of 100 mA cm−2, the energy efficiency of the H-CP electrode (85.11%) increases by 10.41% and 4.34%, compared with the corresponding values of unpatterned CP and heat-treated CF electrodes, respectively.