The effects of surface modification on carbon felt electrodes for use in vanadium redox flow batteries

The surface of carbon felt electrodes has been modified for improving energy efficiency of vanadium redox flow batteries. For comparative purposes, the effects of various surface modifications such as mild oxidation, plasma treatment, and gamma-ray irradiation on the electrochemical properties of carbon felt electrodes were investigated at optimized conditions. The cell energy efficiency was improved from 68 to 75% after the mild oxidation of the carbon felt at 500 °C for 5 h. This efficiency improvement could be attributed to the increased surface area of the carbon felt electrode and the formation of functional groups on its surface as a result of the modification. On the basis of various structural and electrochemical characterizations, a relationship between the surface nature and electrochemical activity of the carbon felt electrodes is discussed.

► We observed the physical and chemical changes on the surface of carbon felts after various surface modifications.
► The surface area and chemistry of functional groups formed on the surface of carbon felt are critical to determine the kinetics of the redox reactions of vanadium ions.
► By incorporation of the surface modifications into the electrode preparation, the electrochemical activity of carbon felts could be notably enhanced.