Graphite felts modified with atmospheric pressure plasma jets (APPJs) are applied as electrodes in an allvanadium redox flow battery (VRFB). APPJ flow penetrates deeply into the graphite felt, improving significantly the wettability of the graphite felt inside out and, thereby, enhancing graphite fiberelectrolyte contact during battery operation. The energy efficiency of a VRFB was improved from 62% (untreated) to 76% (APPJ-treated with the scan mode) at a current density of 80 mA cm(-2), an improvement of 22%. The efficiency improvement is attributed to the oxygen-containing groups and nitrogen doping introduced by N-2 APPJs on the fiber surfaces of graphite felt, both of which enhance electrochemical reactivity. (C) 2014 Elsevier B.V. All rights reserved.