Preparation and electrochemical properties of NiMnO3@NiO nanosheets for pseudocapacitors

Abstract A high-capacitance NiMnO3@NiO nanosheet hybrid material supported on a carbon fiber paper substrate was successfully synthesized for the binder-free electrodes of high-performance supercapacitors. The synthesis involved a two-step solvothermal method followed by annealing. The sample was characterized by X-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectrophotometry techniques. A series of electrochemical measurements, including cyclic voltammetry, galvanostatic charge–discharge, and electrochemical impedance spectroscopy, were carried out to evaluate the electrochemical performance of the sample in a three-electrode system. Results showed that the NiMnO3@NiO electrode exhibited a considerably higher specific capacitance (1090 F g−1 or 151.4 mAh g−1 at a current density of 1 A g−1 and 810 F g−1 or 112.5 mAh g−1 at 10 A g−1) in 4 M KOH electrolyte than its corresponding NiMnO3 and NiO electrodes prepared through a simple one-step hydrothermal method followed by annealing (752 F g−1 or 104.4 mAh g−1 for NiMnO3 and 551.8 F g−1 or 76.7 mAh g−1 for NiO). The NiMnO3@NiO electrode also exhibited excellent cycling stability with a capacitance retention of 89.6% after 5000 cycles at 10 A g−1, which primarily benefited from the unique architecture of the hybrid material. The asymmetric supercapacitor device assembled with the NiMnO3@NiO electrode and an activated carbon electrode presented an energy density of 28.1 Wh kg−1 at a power density of 750 W kg−1 and good cycling stability (∼86.7% retention after 5000 cycles). This excellent electrochemical performance indicated the high potential of NiMnO3@NiO as an integrated electrode material for high-performance supercapacitors.