Siegenite (also called grimmite, or nickel cobalt sulfide) is a ternary transition metal dichalcogenide compound with the chemical formula (Ni,Co)3S4.

It has been actively studied as a promising material system for electrodes in electrochemical energy applications due to its better conductivity, greater mechanical and thermal stability, and higher performance compared to metal oxides currently in use.

[5] Potential applications of this material system include supercapacitors, batteries, electrocatalysis, dye-sensitized solar cells, photocatalysis, glucose sensors, and microwave absorption.

[8] Siegenite was first described in 1850 for an occurrence in the Stahlberg Mine in Müsen, Siegerland, North Rhine-Westphalia, Germany and named for the locality.

[2] It occurs in hydrothermal copper-nickel-iron sulfide bearing veins associated with chalcopyrite, pyrrhotite, galena, sphalerite, pyrite, millerite, gersdorffite and ullmannite.

[3] It occurs in a variety of deposits worldwide, including Brestovsko in the central Bosnian Mountains of Serbia; at Kladno in the Czech Republic; Blackcraig, Kirkcudbrightshire, Scotland.

[9][10] Unlike many binary and ternary semiconductor oxides, NiCo2S4 exhibits metallic properties and high electrical conductivity, which makes it useful as an electrode material in energy storage devices.

[9] Reported synthetic routes of nickel cobalt sulfide include hydrothermal[11][12] and solvothermal[13] reactions, solvent-free thermal decomposition of xanthates,[14] SILAR method for thin films,[15] and solution-phase organometallic synthesis.

[16] The hydrothermal reaction is the most widely used synthesis method to fabricate intricate nanostructures on highly porous substrates, yielding hierarchical structures that maximize redox-active surface areas and promote high-rate supercapacitive performance of Ni-Co-S-based electrodes.

Since the electronegativity of sulfur is lower than that of oxygen, (Ni,Co)3S4 has a more flexible lattice compared to its oxide counterpart, which allows easier electron and ion transport through the structure.