Facile segmented graphite felt electrode for iron-vanadium redox flow batteries with deep eutectic solvent (DES) electrolyte

In this work, the graphite felt electrode for an iron-vanadium redox flow battery (RFB) with deep eutectic solvent (DES) electrolyte is modified by the method of electrolysis in ammonium sulfate, and a segmented electrode is prepared by combining the pristine graphite felt part and the modified part. The electrolysis process not only makes the outermost layer of graphite felt partially fall off which enlarges the specific surface area, but also increases the number of oxygen-containing functional groups on the surface of the graphite felt. To uniform the electrochemical reaction along the electrolyte flow direction and reduce the over-potential, the pristine graphite felt part of the segmented electrode is placed in the electrolyte inlet region, and the modified graphite felt part is put in the outlet region. With the segmented electrode, the single cell test shows the maximum power density is 10.63% higher than that of the pristine electrode under the same operating condition, and the energy efficiency is also higher for charge-discharge cycles. Therefore, the accessibly prepared segmented electrode is promising for improving the performance of the DES electrolyte redox flow battery.