Molybdenum sulfides—efficient and viable materials for electro - and photoelectrocatalytic hydrogen evolution

Abstract

This perspective covers the use of molybdenum disulfide and related compounds, generally termed MoS_x, as electro- or photoelectrocatalysts for the hydrogen evolution reaction (HER). State of the art solutions as well as the most illustrative results from the extensive electro- and photoelectrocatalytic literature are given. The research strategies currently employed in the field are outlined and future challenges pointed out. We suggest that the key to optimising the HER activity of MoS₂ is divided into (1) increasing the catalytic activity of the active site, (2) increasing the number of active sites of the catalyst, and (3) improving the electrical contact to these sites. These postulations are substantiated by examples from the existing literature and some new results. To demonstrate the electrocatalytic properties of a highly conductive MoS₂ hybrid material, we present the HER activity data for multi-wall MoS₂ nanotubes on multi-wall carbon nanotubes (MWMoS₂@MWCNTs). This exemplifies the typical data collected for the electrochemical HER. In addition, it demonstrates that the origin of the activity is closely related to the amount of edges in the layered MoS₂. The photoelectrocatalytic HER is also discussed, based on examples from literature, with an emphasis on the use of MoS_x as either (1) the co-catalyst providing the HER activity for a semiconductor, e.g. Mo₃S⁺ ₄on Si or (2) MoS₂ as the semiconductor with an intrinsic HER activity. Finally, suggestions for future catalyst designs are given.