Template-free synthesis of Ni7S6 hollow spheres with mesoporous shells for high performance supercapacitors

Abstract

Ni₇S₆ hollow spheres with mesoporous shells were successfully synthesized by a novel and facile hydrothermal process without any template or surfactant using nickel chloride hexahydrate and sodium thioglycolate as starting materials. The morphology and microstructure of the samples were examined by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), selected area electron diffraction (SAED), energy dispersive spectroscopy (EDS), and N₂ adsorption–desorption isotherm measurement. A bubble template-based ripening process was proposed for the formation of Ni₇S₆ hollow spheres with mesoporous shells. When applied as electrode materials for supercapacitors, the as-prepared Ni₇S₆ hollow spheres with mesoporous shells exhibited tremendous pseudocapacitance of 2329.5 F g⁻¹ at 2 mV s⁻¹ and 2283.2 F g⁻¹ at 1 A g⁻¹. A capacity retention of 97.1% was achieved even after 1000 cycles. The maximum energy density is 50.7 W h kg⁻¹ at a current density of 1 A g⁻¹. The excellent capacitive performance is attributed to their unique hollow structure with mesoporous shells providing fast ion and electron transfer, and high electronic conduction. These results suggest that the Ni₇S₆ hollow spheres with mesoporous shells are highly promising candidates for supercapacitor electrodes.