“…While Pt is currently championed as the most efficient HER catalyst owing to its nearly thermoneutral H adsorption, scalability of systems based upon noble metals is hindered by high production costs engendered by elemental scarcity. , Many cases in nature (e.g., hydrogenase and nitrogenase enzymes) have succeeded in achieving favorable Δ G H with earth-abundant catalyst compositions that often include non-precious transition-metal chalcogenides with Fe, Ni, and Mo at their active sites. , These revelations highlighted the promise of inorganic analogues such as MoS 2 , where H adsorption at edge sites indeed approaches the Δ G H of Pt. , This observation is consistent with the popular d-band center model which suggests that HER reactivity correlates with the density of transition-metal d states near the Fermi level of the catalyst . Recent advances have identified a range of transition-metal dichalcogenides such as WS 2 , , FeS 2 , , CoS 2 , , WSe 2 , MoSe 2 , − CoSe 2 , , and CoTe 2 , as active catalysts for HER. It is believed that the HER activity of this family of compounds relies on the negatively polarized chalcogenide anions, which results in lower free-energy barriers for proton adsorption …”