Transition metal nitrides and oxynitrides are promising candidates for the application in electrodes of supercapacitors. In this manuscript characterization of tungsten oxynitride and its electrochemical properties in a range of aqueous electrolytes (1 M H2SO4, 1 M KOH, 3 M KCl, 3 M NaCl, 1 M LiCl and 1 M CaCl2) are presented. The electrochemical behavior of tungsten oxynitride depends strongly on the type of cation present in the electrolyte, and the highest capacitance value of 85 F g(-1) is measured in 1 M H2SO4. Cyclic stability in the acid, neutral and alkaline electrolytes is evaluated, and the highest stability is observed in 1 M KOH electrolyte. Possible charge-discharge mechanisms are discussed, and the contribution of a pseudocapacitive mechanism in addition to the electric double-layer formation is proposed. (C) 2012 Elsevier B.V. All rights reserved.