Nanopolygons of Monolayer MS2: Best Morphology and Size for HER Catalysis

With first-principles calculations, we find a new strategy for developing high-performance catalysts for hydrogen evolution reaction (HER) via controlling the morphology and size of nanopolygons of monolayer transition-metal dichalcogenides (npm-MS 2, with M = Mo, W, or V). Particularly, through devising a quantitative method to measure HER-active sites per unit mass and using such HER site density to comparatively gauge npm-MS 2 performance, we identify three keys in making npm-MS 2 with optimal HER performance: (a) npm-MS 2 should be triangular with each edge being M-terminated and each edge-M atom passivated by one S atom; (b) each edge of npm-MoS 2 and WS 2 should have 5–6 metal atoms as HER site density drops below/above these sizes optimal both for HER and practical npm growth; and (c) npm-VS 2 is immune to this overly fastidious size dependence. Known experimental data on npm-MoS 2 indeed support the plausibility of practicing these design rules. We expect that raising the nucleation density and controlling the growth time to favor the production of our proposed ultrasmall npm-MS 2 are critical but practical. Research on npm-VS 2 would bear the highest impact because of its size-forgiving HER performance and relatively high abundance and low cost.