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 TiO2 single crystal wafers, both neat and Pt-loaded, focusing on H2 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 H2 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 H2 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 TiO2-based photocatalysts for hydrogen generation.