Self-assembled synthesis of hierarchically porous NiO film and its application for electrochemical capacitors

A hierarchically porous NiO film on nickel foam substrate is prepared by a facile ammonia-evaporation method. The self-assembled film possesses a structure consisting of NiO triangular prisms and randomly porous NiO nanoflakes. The pseudocapacitive behaviors of the porous NiO film are investigated by cyclic voltammograms and galvanostatic charge–discharge tests in 1 M KOH. The hierarchically porous NiO film exhibits a high discharge capacitance and excellent rate capability with 232 F g−1, 229 F g−1, 213 F g−1 and 200 F g−1 at 2, 4, 10, and 20 A g−1, respectively. The specific capacitance of 87% is maintained from 2 A g−1 to 20 A g−1. The porous NiO film also shows rather good cycling stability and exhibits a specific capacitance of 348 F g−1 after 4000 cycles.