We, for the first time, demonstrate a facile preparation of N, O dual-doped carbon felt (CF) as electrodes in all-vanadium redox flow batteries (VRFB). N2 and O2 plasma was employed to treat the CF, introducing nitrogen and oxygen atoms doped into the carbon felt to result in the improved electrocatalytic activity and enhanced interaction of CF-electrolyte during the battery operation. The energy efficiency of the as-assembled VRFB is improved from 65% (pristine) to 78% (doped) at a current density of 50 mA cm-2 with excellent cycling stability.