A facile template-free approach for the solid-phase synthesis of CoS2 nanocrystals and their enhanced storage energy in supercapacitors

Sphere-like CoS2 nanocrystals (NCs) with porous surfaces were prepared by a modified molten-salt synthesis (MSS) method under mild reaction conditions. Thiourea was used as a reactant, flux and structure-directing agent in the synthesis of CoS2 NCs, which led to mild reaction conditions, pure product and a porous spherical surface. The increase of reaction temperature and molar ratio of cobalt nitrate to thiourea results in larger CoS2 NCs and the change of their morphologies from spheroidal to angular. The synthesis mechanism of CoS2 nanocrystals includes three steps which are the formation of sphere-like CoS2 NCs at the early reaction stage, the formation of a porous structure on the CoS2 NC surface and the aggregation of NCs. The specific surface area of CoS2 NC electrodes reached 29.30 m(2) g(-1) which results in a specific capacitance as high as 654 F g(-1). These results demonstrate that CoS2 NCs can be produced on a large scale through a simple solid-phase synthesis pathway and that they will be a promising electrode material for supercapacitors.