Copper (II) sulfide is a chemical compound of copper and sulfur. It occurs in nature as the dark indigo blue mineral covellite. It is a moderate conductor of electricity. A black colloidal precipitate of CuS is formed when hydrogen sulfide, H2S, is bubbled through solutions of Cu(II) salts. It is one of a number of binary compounds of copper and sulfur, and has attracted interest because of its potential uses in catalysis and photovoltaics.

Structure and bonding:
Copper sulfide crystallizes in the hexagonal crystal system, and this is the form of the mineral covellite. There is also an amorphous high pressure form which on the basis of the Raman spectrum has been described as having a distorted covellite structure. An amorphous room temperature semiconducting form produced by the reaction of a Cu(II) ethylenediamine complex with thiourea has been reported, which transforms to the crystalline covellite form at 30 °C. Covellite was the first identified naturally occurring superconductor. Uses of covellite CuS superconductivity research can be seen in lithium batteries’ cathodes, ammonium gas sensors, and solar electric devices with metal chalcogenide thin films. The reaction of copper with molten sulfur followed by boiling sodium hydroxide and the reaction of sodium sulfide with aqueous copper sulfate will also produce copper sulfide.

Nanostructures:
The electron mobility and free hole density characteristics of covellite makes it an attractive choice for nanoplatelets and nanocrystals because they provide the structures the ability to vary in size. However, this ability can be limited by the platelike structure all copper sulfides possess. Its anisotropic electrical conductivity has been experimentally proven to be greater within layers. Researchers have shown that covellite nanoplatelets of approx. two nm thick, with one unit cell and two copper atoms layers, and diameters around 100 nm are ideal dimensions for electrocatalysts in oxygen reduction reactions (ORR).





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