Non-substituted γ-MnO2 and γ-Mn1−y A y O2−δ (A=Co, Al) compounds synthesized by the electrochemical–hydrothermal route have been studied as active electrode materials for aqueous electrochemical supercapacitors. Advantage of the Mn to Co or Al substitution was taken in order to increase the surface area of γ-Mn1−y A y O2−δ materials, thus leading to enhanced supercapacitive behavior. The effect of the surface area on the specific capacitance value and its origin, i.e. double layer or faradic, is discussed.