Photocatalysis on thin films: exploring spatial and compositional control

Abstract

The rational design of functional materials that convert solar energy into chemical fuels is a central challenge in modern materials chemistry, heterogeneous catalysis and sustainable energy research. Achieving this goal requires not only the development of highly active photocatalysts but also a fundamental understanding of how catalyst architecture and interfacial structure govern photocatalytic function across multiple length scales. While TiO2-based photocatalysts have been extensively investigated, comparatively little is known about how the spatial distribution of photodeposited cocatalysts influences localized photocatalytic activity on immobilized thin films. This thesis addresses this knowledge gap through slit definedphotodeposition of noble-metal cocatalysts (Pt, Au, Ag, Cu andNi) onto TiO2-coated glass substrates, followed by continuous-flow, spatiallyresolved photocatalytic hydrogen evolution (HER) measurements. The effects of cocatalyst identity, loading, deposition geometry, deposition environment and alkaline precursor chemistry on localized HER were systematically investigated. Grazing-incidence X-ray diffraction (GI-XRD), X-ray photoelectron spectroscopy (XPS) and UV–Vis diffuse reflectance spectroscopy (UV–Vis DRS) were employed to correlate structural, chemical and optical properties with photocatalytic performance. Pt exhibited the highest HER activity under UV irradiation, whereas Au displayed characteristic plasmonic absorption but lower hydrogen evolution. Most significantly, spatial HER mapping consistently revealed hydrogen evolutionbeyond the nominally photodeposited regions, even after liquid–liquidinterfacial masking and alkaline photodeposition designed to confine cocatalystdeposition. These findings demonstrate that localized photocatalytic activity cannot be inferred solely from the nominal cocatalyst pattern but is governed by the interplay between deposition chemistry, semiconductor charge transport and catalyst–support interactions. Overall, this work establishes a general experimental methodology for correlating spatially engineered cocatalyst architecture with localized photocatalytic function in immobilized TiO2 thin films, thus providing a general experimental framework for correlating cocatalyst architecture with localized photocatalytic function in immobilized semiconductor films.