Supercapacitive performance of single phase CuO nanosheet arrays with ultra-long cycling stability

Copper oxide nanofilms can be fabricated on Cu foam by a simple electrochemical anodization process. However, it is difficult to obtain single-phase nanofilms that consist only of Cu2O or CuO. In this work, we present a modified anodization process that includes (NH4)6Mo7O24·4H2O in the electrolyte solution, and prepare single-phase CuO nanofilms grown directly on Cu foam. The surface morphologies of the CuO nanofilms are greatly dependent on the concentration of (NH4)6Mo7O24·4H2O included in the electrolyte solution during the anodization process, and accordingly present nanodots, nanoflakes, nanosheets, and/or nanobelts. The synthesis mechanism for CuO nanofilms is discussed in detail. The as-fabricated single-phase CuO nanofilms can be directly employed as electrodes that exhibit good supercapacitive performance, with an areal capacitance greater than 600 mF cm-2 at a current density of 1 mA cm−2 in a 2 M KOH aqueous solution. Moreover, the single-phase CuO nanofilm electrodes also demonstrate excellent long term cycling stability with about 94% retention of the initial areal capacitance after 10,000 charge/discharge cycles. The results demonstrate that the CuO nanofilms prepared on Cu foam by our modified anodization process are promising electrode materials for high-performance flexible supercapacitors.