Synthesis of Activated Graphite Felts Using Short-Term Ozone/Heat Treatment for Vanadium Redox Flow Batteries

A new combined method of ozone exposure and thermal treatment is developed as a method of activating graphite felt electrodes for use in vanadium redox flow batteries (VRFB). The physical and electrochemical properties of ozone/heat-treated graphite felt was compared with the conventional air/heat treated graphite felts. The results demonstrated that the ozone/heat-treated graphite felt had higher specific surface area and oxygen content compared with the conventional air/heat-treated graphite felts. The ozone/heat treatment method is also very selective in the formation of carboxylic group which is active toward vanadium redox reaction. The performance improvement of the ozone/heat treated graphite felt was significant. It is notable that the ozone/heat treatment was performed at a temperature as low as 180°C for just 6 min. This temperature is a considerably milder condition compared with the conventional air/heat treatment process that requires long treatment time (5 hours) and high temperature of 500°C. This property indicates that the ozone/heat treatment is a cost-effective and practical method for activating graphite felt that is used in VRFB.