Ionic liquid derived nitrogen-doped graphite felt electrodes for vanadium redox flow batteries

Abstract

A facile method for preparing nitrogen-doped graphite felt electrodes with high electrocatalytic activity for vanadium redox flow batteries (VRFBs) is developed. These nitrogen-doped graphite felts are fabricated by coating 1-ethyl-3-methylimidazolium dicyanamide (EMIM dca) on the surface of graphite felts followed by thermal treatment under a N2 atmosphere. EMIM dca, an ionic liquid containing a high content of nitrogen, is used as an effective precursor for nitrogen doping on graphite felt surfaces. The physical and electrochemical properties of the nitrogen doped graphite felts are characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry (CV). When employed in charge-discharge tests, the single cells with the nitrogen doped graphite felts show outstanding performance. The graphite felt coated with 20 wt% EMM dca solution (GF-Ed20) exhibits three times increased discharge capacity and 10% higher energy efficiency at a current density of 150 mA cm−2 compared to the graphite felt with the oxygen functional groups (GF-Ref) prepared by the conventional heat treatment method. The improved performance is attributed to the high nitrogen content on the graphite felt, which increases the electrocatalytic activity of vanadium redox reactions.