Spatiotemporal Mapping of Field-Driven Electron Spillover across ZnO Facets

Efficient spatial separation of photogenerated charge carriers remains a formidable challenge in photocatalysis. Here, we employ in situ Kelvin probe force microscopy (KPFM) to reveal unexpected electron accumulation on nonpolar {01 $\overline{1}$ 0} facets in wurtzite ZnO platelets (N-ZnO), which represents a dynamic "electron spillover" process beyond static facet confinement. Crucially, femtosecond transient absorption (fs-TA) spectroscopy directly captures interfacial electron transfer from polar Zn-terminated (0001) facets (Zn-ZnO) to N-ZnO with a lifetime of 60.82 ps. However, electrons spilling over from Zn-ZnO to N-ZnO recombine with the photogenerated holes inherent to N-ZnO, thereby turning it into a recombination center. Guided by this insight, we construct a dual-cocatalyst architecture (AuZnOCo): Au is selectively anchored on N-ZnO and Zn-ZnO to extract electrons, and Co₃O₄ is deposited on O-terminated (000 $\overline{1}$ ) facets (O-ZnO) to trap holes. The loading of dual cocatalysts promotes charge separation and suppresses this electron spillover‑induced recombination. Quantitative analysis reveals ≈3739 holes localized on O-ZnO, ≈1771 electrons on Zn-ZnO, and ≈812 electrons on N-ZnO in AuZnOCo, while the electron diffusion length (L) increases from 81.41 to 121.77 nm. This work deciphers the spatiotemporal resolution of charge-carrier dynamics, offering a blueprint for rationally engineering anisotropic photocatalysts.