Direct electrochemical identification of rare microscopic catalytic active sites.

Local voltammetric analysis with a scanning electrochemical droplet cell technique, in combination with a new data processing protocol (termed data binning and trinisation), is used to directly identify previously unseen regions of elevated electrocatalytic activity on the basal plane (BP) of molybdenum disulfide (2H-MoS). This includes BP-like structures with hydrogen evolution reaction activities approaching that of the edge plane and rare nanoscale electrocatalytic "hot-spots" present at an areal density of approximately 0.2-1 μm. Understanding the nature of (sub)microscopic catalytic active sites, such as those identified herein, is crucial to guide the rational design of next-generation earth-abundant materials for renewable fuels production.