Single-Molecule Visualization of Nanoscale Spatiotemporal Dynamics of Charge-Carrier-Driven Photocatalysis on 2D InSe.

The photocatalytic performance of two-dimensional (2D) semiconductors is governed by the intricate interplay between nanoscale surface structures and charge-carrier dynamics. However, ensemble-averaged and ex situ measurements obscure the spatial heterogeneity and temporal fluctuations, limiting mechanistic understanding. Here, we employed single-molecule fluorescence imaging to quantitatively visualize the photocatalytic activity of 2D layered InSe at the nanoscale, differentiating the carrier extraction positions and efficiencies of photogenerated holes and electrons for light-driven semiconductor-catalyzed oxidation reactions. We observed that hole-driven activity occurs on both the basal planes and edges, whereas electron-driven reactivity is confined primarily to the edges. Temporal analysis of single-turnover events uncovered catalysis-induced dynamic fluctuations, governed by surface-adsorbate interactions, with thicker direct-band gap flakes exhibiting enhanced temporal stability. Spatially, activity fluctuations correlate positively along individual edges over ∼150 nm, suggesting communication via charge diffusion along the edge. Furthermore, reactivity decays exponentially from the edges into the basal plane over hundreds of nanometers, attributed to carrier redistribution from edge defects to pristine regions. These discoveries offer nanoscale insight into the spatiotemporal heterogeneity of photocatalysis.