TiOxNy and VOxNy powders have been synthesized using oxide precursors and a conventional nitridation method. It enables to control of oxygen content and surface area. The electrochemical performances of the different powders have been investigated. A strong dependence on the surface area as well as on the nature of the oxynitride has been found. A typical value of 300 mu F cm(-2) has been determined for VOxNy powders, while TiOxNy powders only show 50 mu F cm(-2). In this last case it is believed that only double layer capacitance or weak redox reactions participate in charge storage mechanism while for vanadium based oxynitrides, a thin layer below the surface (approximate to 4 angstrom) is involved in charge storage via faradic reactions. VOxNy electrodes can be operated in different aqueous electrolytes, but only double layer capacitance is measured in neutral electrolytes. The highest capacitance values (approximate to 80 F g(-1)) are measured in KOH and fair cycling ability is achieved when the electrochemical window is limited, thus avoiding oxidative potentials. (C) 2012 Elsevier Ltd. All rights reserved.