Facet-Dependent Photocatalytic Activity of Rutile and Anatase Single Crystals in the Presence and Absence of a Pt Cocatalyst

This study investigates the facet-dependent photocatalytic activity of rutile and anatase TiO 2 single crystal wafers, both neat and Pt-loaded, focusing on H 2 evolution and methanol reforming to formaldehyde. For well-defined rutile facets (100), (110), (111), and (001), we identify a clear reactivity trend: (111) > (001) > (100) > (110). Remarkably, the rutile (111) facet shows significant H 2 evolution even without a Pt cocatalyst and in plain water─outperforming all other rutile and anatase facets (101) and (001). In contrast, low-energy facets like rutile (100) and (110) require Pt to enable H 2 production, indicating that methanol reforming dominates on these surfaces, while direct conduction band electron transfer is operative on high-energy facets. These findings clarify long-standing discrepancies in the literature and remarkably well match a wide range of theoretical predictions on surface energy and band edge positions on respective facets and polymorphs. Our results emphasize the importance of (junction-free) facet control when comparing experimental activity and theoretical work and highlight the notably higher reactivity of the (111) rutile facet in view of TiO 2 -based photocatalysts for hydrogen generation.