Cu-doped NiO for aqueous asymmetric electrochemical capacitors

In this work, the influence of Cu doping on the electrochemical properties of NiO was investigated regarding its performance as electrodes in aqueous supercapacitors. NiO and Ni1−xCuxO (x=0.5–3%) cathode materials were synthesized via a citrate-gel process. Ni1−xCuxO samples have the same crystal structures as those of the un-doped NiO, indicating that copper atoms enter into the lattice of nickel mono-oxide. Compared to NiO, Cu-doping materials significantly improve the specific capacitance and rate capability. Especially, among all of the investigated samples, Ni0.99Cu0.01O presents the best electrochemical performance as high as 559 and 389 F g−1, which are 90.14% and 86.12% higher than those of NiO at 0.3 and 10 A/g, respectively. This work demonstrated that Cu-doping is an effective way to improve the pseudo-capacitance of nickel monoxide.