Nanoscale Observation of Photocatalytic Hydrogen Evolution on Ultrathin Catalysts at the Single-Entity Level

The advancement of two-dimensional (2D) photocatalysts is significantly hampered by the inability to perform quantitative, single-entity performance measurements, a capability already established for electrocatalytic counterparts. Here, using chemically synthesized, single-crystalline 2D BiOCl as a model catalyst, we report, for the first time, the accurate measurement of the photocatalytic hydrogen evolution rate at the single-catalyst level. More importantly, by integrating liquid-phase atomic force microscopy and total internal reflection fluorescence microscopy, we reveal that active sites on 2D BiOCl flakes are edge-enriched and spatially localized. Guided by this spatial distribution, we activated the basal plane of the 2D catalysts through plasma etching and elucidated the mechanism of this performance enhancement using density functional theory calculations. This work demonstrates that, by resolving the structure-activity relationship at the single-entity level, we can unlock the full catalytic potential of 2D materials, paving the way for the rational engineering of highly efficient photocatalysts.