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

Abstract

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 m² 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.