Effect of nitrogen functionalization of graphite felt electrode by ultrasonication on the electrochemical performance of vanadium redox flow battery

Abstract In this paper, facile approach for preparing nitrogen-functionalized graphite felt (GF) as electrodes in vanadium redox flow battery was developed and investigated. Modification was done via ultrasonication-assisted self-polymerization and subsequent pyrolysis of dopamine to produce nitrogen-functionalized graphite felt. The electrode surface changed from hydrophobic to hydrophilic and charge transfer resistance was reduced upon nitrogen functionalization, leading to improved electrochemical properties. To achieve high electrochemical performance, the degree of nitrogen functionalization was optimized by evaluating the characteristics, such as surface area, porosity, and cyclic voltammogram, of GF and various nitrogen-functionalized GF (NGF) samples. All NGF samples showed improved energy efficiency in a VRFB single cell test. Specifically, the optimized sample, NGF05 (containing 0.5 mM dopamine), had a higher energy efficiency (75.5%) than GF (69.2%) at a current density of 150 mA cm−2. Moreover, the electrolyte utilization efficiency of NGF05 (68.1%) was higher than that of GF (58.2%). Thus, nitrogen functionalization of GF by ultrasonication is a simple, practical approach to produce high-performance VRFBs.