MoS x -type catalysts belong to this group of materials. It was shown for hexagonal MoS 2 that the sulfur atoms at edge sites of (00.1)-facets act as active centers for the HER, their catalytic efficiency being comparable to that of platinum. As the vdW basal planes are catalytically inert, nanoparticles are of interest for increasing the number of active sites at the edges of the hexagonal planes. Recently, it was reported that ammonium thiomolybdate (NH 4 ) 2 Mo 3 S 13 nanoclusters showed an even better performance in the HER in comparison to MoS 2 nanoparticles. This catalyst is characterized by a high number of catalytically active [S 2 ] 2-sites.