High performance nitrogen-doped graphite felts are successfully prepared via urea hydrothermal treatment at low temperatures below 180 degrees C and is demonstrated as enhanced electrodes for vanadium redox flow batteries. Effect of urea hydrothermal treatment temperature on the nitrogen-bonding configurations is investigated. Properties of the modified graphite felts including morphology, cyclic voltammetry, X-ray photoelectron spectroscopy and cell performance of vanadium redox flow battery are characterized. Taking advantage of the increased pyridinic-N content, the prepared nitrogen-doped graphite felt presents an outstanding electrochemical performance, which exhibits 8.35% increase of energy efficiency (up to 81.32%) at a high current density of 150 mA cm(-2). (c) 2019 The Electrochemical Society.