Photocarrier Transport Mechanisms in Amorphous and Epitaxial TiO2/SrRuO3 Heterojunction Photocatalysts

Heterojunction photocatalysts in thin-film form offer the possibility of improved optical absorption of solar radiation but have found limited use due to various material challenges. Epitaxial structures based on strontium ruthenate (SRO) and TiO2 have demonstrated unexpectedly high activity under visible-light-only illumination because of strong absorption by the SRO, high electrical conductivity, and the ability to inject hot electrons into the active TiO2 photocatalyst. The role of photoholes, the mechanisms of carrier transport to the TiO2 surface, and the necessity of an epitaxial structure remain unclear. The present work helps to fill these gaps through rate measurements of methylene blue (MB) photooxidation on SRO–TiO2 under visible light, together with photoemission measurements of interfacial and free surface band edges of the TiO2. Diffusive transport of thermalized holes appears sufficient to explain the results, and surprisingly, a heterojunction based on amorphous SRO and TiO2 retains a grea...