The nature of active sites of molybdenum sulfide-based catalysts for hydrogen evolution reaction

It is particularly important to investigate the structure–activity relationships between the catalytic active sites and the catalytic activity. Molybdenum sulfide has been widely studied as a representative transition metal dichalcogenides-based catalyst in the field of catalytic hydrogen evolution reaction (HER). The atomic structures of active sites of crystalline molybdenum disulfide are very unambiguous, while the catalytic HER mechanism of amorphous molybdenum sulfide (a-MoSx) has been controversial due to the diverse atomic structures of active sites in a-MoSx. It is urgent to find out the nature of true active sites of a-MoSx to further design efficient HER active sites with precise atomic structures. So far, the researchers have explored various HER mechanisms of a-MoSx combining in-situ characterization with density functional theory calculations. These mechanisms are not uniform or even diametrically opposed. Here, various HER mechanisms of a-MoSx were summarized systematically. In view of the current research status, the nature of active sites of molybdenum sulfide-based catalysts for HER is still difficult to determine. This review would be significant for further revealing the nature of active sites of molybdenum sulfide-based catalysts for HER.