Ammonia-induced N-doped NiCoO2 nanosheet array on Ni foam as a cathode of supercapacitor with excellent rate performance

Transition metal oxides as the electrode material of supercapacitors have been widely studied due to their high energy density. However, relatively low power density resulting from poor conductivity of the metal oxides limits their application. In this paper, a new N-doped NiCoO2 nanosheet array on Ni foam was synthesized through an ammonia-induced reduction strategy. During the ventilation of NH3 in the ammonia annealing stage, N was doped into the structure of NiCoO2, which leads to increased concentration of oxygen vacancies and improved conductivity. As a positive electrode, N-doped NiCoO2 exhibits excellent rate performance (1449.3 F g−1 at 1 A g−1 and 1190.4 F g−1 at 50 A g−1) and impressive cycle stability (the capacitance retention ratio is 92% after 5000 cycles at the current density of 40 A g−1) compared to undoped NiCoO2 nanosheet array electrode. Assembling it as the positive electrode and activated carbon as the negative electrode, the aqueous asymmetric supercapacitor exhibits high power density, energy density, and excellent rate performance. The remarkable energy storage performances make N-doped NiCoO2 nanosheet arrays material (N-NiCoO2) have a broad application prospect in the field of supercapacitors.