Self-optimizing, highly surface-active layered metal dichalcogenide catalysts for hydrogen evolution

Low-cost, layered transition-metal dichalcogenides (MX2) based on molybdenum and tungsten have attracted substantial interest as alternative catalysts for the hydrogen evolution reaction (HER). These materials have high intrinsic per-site HER activity; however, a significant challenge is the limited density of active sites, which are concentrated at the layer edges. Here we unravel electronic factors underlying catalytic activity on MX2 surfaces, and leverage the understanding to report group-5 MX2 (H-TaS2 and H-NbS2) electrocatalysts whose performance instead mainly derives from highly active basal-plane sites, as suggested by our first-principles calculations and performance comparisons with edge-active counterparts. Beyond high catalytic activity, they are found to exhibit an unusual ability to optimize their morphology for enhanced charge transfer and accessibility of active sites as the HER proceeds, offering a practical advantage for scalable processing. The catalysts reach 10 mA cm−2 current density at an overpotential of ∼50–60 mV with a loading of 10–55 μg cm−2, surpassing other reported MX2 candidates without any performance-enhancing additives. Metal dichalcogenides are promising electrocatalysts for hydrogen evolution, but more active and stable materials are desired. Here the authors demonstrate that H-TaS2 and H-NbS2 possess high basal-plane activity that increases with cycling through changes in the morphology of the catalysts.