Layered 2D PtX₂ (X = S, Se, Te) for the electrocatalytic HER in comparison with Mo/WX₂ and Pt/C: are we missing the bigger picture?

The hydrogen evolution reaction (HER) is best catalyzed by metallic Pt with the lowest overpotential, Tafel slope, and highest exchange current density. But its scarcity made us look for abundant alternatives which come at the price of poor activity and stability. Hence, all non-Pt HER electrocatalysts are compared with Pt (often Pt/C). In such cases, a closer activity to that of Pt is usually appreciated for non-Pt materials. In contrast, when an HER electrocatalyst is made of Pt, it is expected to surpass the activity of Pt/C as it has the same Pt. A familiar example of this kind is the dilution of Pt without any compromise in activity. The recently evolved layered dichalcogenides of Pt (PtX₂) do not satisfy this expectation as they not only perform poorer than Pt/C but also against other familiar MX₂ HER electrocatalysts such as MoX₂ and WX₂. However, the studies that engaged in the evaluation of the HER activity of PtX₂ were quite useful in deducing the structure-activity relationship and mechanism which are clearly inevitable pieces of knowledge needed in all kinds of electrocatalysis. Though PtX₂ are poorer HER catalysts in their pristine form, structural engineering and other activation methods made them as active as Pt/C while a few were better than Pt/C. This perspective is dedicated to presenting the recent progress in the area of the PtX₂ catalyzed HER in comparison with MoX₂ and WX₂ while highlighting the opportunities and challenges. Particularly, how we are missing the bigger picture in designing a Pt-based HER electrocatalyst and the ways in which poorly active PtX₂ can be made into a superior one to Pt/C are critically discussed.