Cobalt(II) sulfide
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| Identifiers | |
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PubChem CID
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| RTECS number | GG332500 |
| Properties | |
| CoS (varied) | |
| Molar mass | 90.9982 g/mol |
| Appearance | black solid (alpha) grayish-red crystals (beta) |
| Density | 5.45 g/cm3 |
| Melting point | 1195 °C |
| 0.00038 g/100 mL (18 °C) | |
| Solubility | slightly soluble in acid |
| +225.0·10−6 cm3/mol | |
| Structure | |
| octahedral (beta) | |
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Cobalt sulfide is the name for chemical compounds with a formula CoxSy. Well-characterized species include minerals with the formula CoS, CoS2, Co3S4, and the synthetic material Co9S8. In combination with molybdenum, the sulfides of cobalt are used as catalysts for the industrial process called hydrodesulfurization, which is implemented on a large scale in refineries. Cobalt sulfide thin films can be used as counter electrodes (CEs) of dye-sensitized solar cells (DSSCs). Several research works demonstrate that CoxSy can be used to substitute the high expensive platinum (Pt), commonly used for the preparation of high efficient CEs. Thin films of CoxSy can be deposited on different substrates using chemical precursor Inks based on organic solvents or water. Also electrochemical techniques are suitable for the preparation of efficient and cheap CoxSy CEs. It has been demonstrated that CoS CEs can be also used in p-type DSSCs.
Cobalt sulfides precipitate when aqueous solutions of cobalt(II) ions are treated with hydrogen sulfide. This reaction is useful in the purification of cobalt from its ores as well as in qualitative inorganic analysis. In general, the sulfides of cobalt are black, semiconducting, insoluble in water, and nonstoichiometric. They react with strong acids to release hydrogen sulfide gas again. They are weak reducing agents and can be oxidized to cobalt sulfate.
Cobalt sulfide exists in two forms: alpha and beta.
The best defined sulfides of cobalt occur as minerals. The rare mineral cattierite has the stoichiometry CoS2. It is isostructural with iron pyrite, featuring disulfide groups, i.e. Co2+S22−. Linnaeite, also rare, has the formula Co3S4 and crystallizes in the spinel motif.
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