A double-layer electrode for the negative side of deep eutectic solvent electrolyte-based vanadium-iron redox flow battery

This work designs a double-layer porous electrode spliced by carbon paper and graphite felt. A low-porosity carbon paper electrode treated by thermal oxidation is assembled near the membrane, which is used to pro-mote the kinetics of vanadium redox reaction, and the increased hydrophilicity of electrode also facilitates the convective mass transfer process. On the other hand, a high-porosity graphite felt electrode deposited with copper nanoparticles is assembled near the flow field, which has the high permeability, conductivity and interface catalytic efficiency to reduce flow/ions/charge transfer resistances. Cyclic voltammetry illustrates that the copper nanoparticles deposited on the surface of carbon electrode can play the role to enhance the elec-trochemical activity of the negative electrode with lower potential. Consequently, the double-layer porous electrode is assembled as a negative side of deep eutectic solvent electrolyte-based vanadium-iron redox flow battery (RFB). The experimental study shows this modified RFB has an energy efficiency of 91.8% at the rela-tively low current density (2 mA cm-2), and a peak power density of 12.71 mW cm-2, which are 12.2% and 30.2% higher than that of pristine graphite electrode, respectively. The results demonstrate the superiority of this design strategy of double-layer electrode for potential applications.