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

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 N-2 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.