Single Atomic Vacancy Catalysis

Single atom catalysts provide exceptional activity. However, measuring the intrinsic catalytic activity of a single atom in real electrochemical environments is challenging. Here, we report the activity of a single vacancy for electrocatalytically evolving hydrogen in two-dimensional (2D) MoS₂. Surprisingly, we find that the catalytic activity per vacancy is not constant but increases with its concentration, reaching a sudden peak in activity at 5.7 × 10¹⁴ cm^-2 where the intrinsic turn over frequency and Tafel slope of a single atomic vacancy was found to be ∼5 s^-1 and 44 mV/dec, respectively. At this vacancy concentration, we also find a local strain of ∼3% and a semiconductor to metal transition in 2D MoS₂. Our results suggest that, along with increasing the number of active sites, engineering the local strain and electrical conductivity of catalysts is essential in increasing their activity.