Novel amorphous nickel sulfide@CoS double-shelled polyhedral nanocages for supercapacitor electrode materials with superior electrochemical properties

Highlights: • The Ni_xS_y@CoS double-shelled polyhedral nanocages are prepared by a facile method. • The Ni_xS_y@CoS nanocages are amorphous and have a typical 3D hollow structure. • The nanocages have a homogenous microstructure and size distribution about 700 nm. • The nanocages display remarkable specific capacitance of 2091 F g⁻¹ at 2 A g⁻¹. • The nanocages have excellent long-term cycle-life as an electrode material. - Abstract: The design and development of durable and high efficient supercapacitors is highly desired in electronic and energy storage devices. Traditional carbon based capacitors suffer from low specific capacitance and energy density. Recently transition metal sulfides are attractive alternatives for crystal electrode materials. Herein we demonstrate a facial design and synthetic method to grow novel metal sulfide double-shelled polyhedral nanocages consisting of mesoporous amorphous Ni_xS_y@CoS via a metal-organic-framework engaged strategy for use in supercapacitors. The Ni_xS_y@CoS polyhedrons with the inner and outer-shells respectively consisting of CoS and Ni_xS_y are obtained at mild room temperature without further thermal-treatment. The outer-shell is easily adjustable to suit various combinations according to the requirement. The morphological and structural evolution of the Ni_xS_y@CoS nanocages was studied systematically. Further electrochemical performance shows that the Ni_xS_y@CoS exhibits remarkably high capacitance of 2291 F g⁻¹ at 1.0 A g⁻¹ in 6 M KOH aqueous solution.