Mn(OH)2-coated Ni3S2 nanosheets on Ni foam as a cathode for high-performance aqueous asymmetric supercapacitors

Abstract

In this work, we report a high-performance self-standing electrode of Mn(OH)2-coated Ni3S2 (Ni3S2@Mn(OH)2) nanosheets on Ni foam by hydrothermally growing the Ni3S2 nanosheets and electrodepositing Mn(OH)2 around Ni3S2. The structure of the Ni3S2 nanosheets grown by the hydrothermal method is more stable, and the electrodeposition method is easier to synthesize Mn(OH)2 without using any binder. The electrochemical characterization demonstrates that combining the Ni3S2 nanosheet with the Mn(OH)2 coating is an effective way to improving the charge storage performance because of the synergetic effects of both materials/structures. The electrode possesses a high area-specific capacitance of 6430.2 mF cm−2 at 1 mA cm−2 and good cycle stability with ~80.9% capacitance retention after 9000 cycles at 8 mA cm−2. The aqueous asymmetric supercapacitors assembled with the Ni3S2@Mn(OH)2 cathode, the activated carbon anode and 1 M KOH electrolyte delivers an energy density of 0.371 mWh cm−2 at 0.799 mW cm−2, as well as good cycle stability with ~86.3% capacity retention after 10,000 cycles at 20 mA cm−2. Given the high performance and relatively simple preparation, this work provides a valuable exploration of developing high-performance cathodes for aqueous supercapacitors.