Preparation and electrochemical properties of NiMnO3@NiO nanosheets for pseudocapacitors

Abstract

A high-capacitance NiMnO 3 @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 NiMnO 3 @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 NiMnO 3 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 NiMnO 3 and 551.8 F g −1 or 76.7 mAh g −1 for NiO). The NiMnO 3 @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 NiMnO 3 @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 NiMnO 3 @NiO as an integrated electrode material for high-performance supercapacitors. A high-capacitance NiMnO 3 @NiO nanosheet hybrid material supported on a carbon fiber paper (CFP) substrate was successfully synthesized for binder-free electrodes of high-performance supercapacitors via a two-step solvothermal method followed by an annealing process. First, a MnO 2 thin coating was electrodeposited on the surface of CFP. Then, it was transformed into NiMnO 3 through hydrothermal conversion in a NiSO 4 soution and heat treatment. Finally, NiO nanosheets were grown and anchored on the surface of the NiMnO 3 by another hydrothermal process in a NiSO 4 solution containing CTAB and heat treatment. The obtained NiMnO 3 @NiO nanosheet electrode shows a highest specific capacitance of 1090 F g −1 (or 151.4 mAh g −1 ) at 1 A g −1 and remarkable cycling performance (∼89.6% retention after 5000 cycles), which can be attributed to its unique microstructures. The asymmetric supercapacitor device assembled with the CFP@NiMnO 3 @NiO electrode and an activated carbon electrode presents 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). • A NiMnO 3 @NiO electrode is fabricated via a solvothermal-based process. • The NiMnO 3 @NiO exhibits a specific capacitance of 1090 F g −1 at 1 A g −1 . • The NiMnO 3 @NiO shows a rate capability of 74.3% at 10 A g −1 . • This material is more economically competitive than the Co-based oxides. • The NiMnO 3 @NiO nanosheets are tightly bound to the CFP current collector.