Oxygen Vacancy-Induced Novel Low-Temperature Water Splitting Reactions on FeO(111) Monolayer-Thick Film

We have used XPS, UPS, and TDS to comparatively study water chemisorption and reaction on stoichiometric FeO(111) monolayer-thick film on Pt(111), stoichiometric FeO(111) monolayer-thick islands on Pt(111), and FeO(111) monolayer-thick films with oxygen vacancies on Pt(111) at 110 K. On stoichiometric FeO(111) monolayer-thick film, water undergoes reversible molecular adsorption. On stoichiometric FeO(111) monolayer-thick islands on Pt(111), water dissociates at coordination-unsaturated Fe­(II) sites of the FeO(111)–Pt­(111) interface to form OH following H₂O + Fe_CUS + FeO → Fe_CUS–O_wH + FeOH in which O_w means O from H₂O. Upon heating, H₂ evolution occurs above 500 K. On FeO(111) monolayer-thick films with oxygen vacancies, water dissociates and molecularly chemisorbs to form a mixed adsorbate layer of H­(a), OH, and H₂O­(a) following both H₂O + Fe–O_vacancy + FeO → FeO_wH + FeOH and H₂O + 2 Fe–O_vacancy → FeO_wH + H­(a)–Fe–O_vacancy. Upon heating, besides the high-temperature H₂ evolution, additional H₂ desorption peaks appear simultaneously with the low-temperature desorption features of adsorbed H₂O­(a), revealing novel low-temperature water splitting reactions. The formation of hydrated-proton surface species within a mixed adsorbate layer of H­(a), OH, and H₂O­(a) on FeO(111) monolayer-thick films with oxygen vacancies is proposed to explain such novel low-temperature water splitting reactions. These results greatly enrich the surface chemistry of water on solid surfaces

Surface Reconstruction-Induced Site-Specific Charge Separation and Photocatalytic Reaction on Anatase TiO₂(001) Surface

Photocatalytic reaction of methanol on an anatase TiO₂(001)-(1 × 4) reconstructed surface, a prototype reaction for photocatalysis, was studied by means of X-ray photoelectron spectroscopy, thermal desorption spectrum, and density functional theory calculations. Photocatalytic oxidation reaction was observed to exclusively occur at the Ti_4C sites of the (1 × 4) added row but not at the Ti_5C sites of the (1 × 1) basal surface. The accompanying density functional theory calculation results demonstrate that the valence band maximum is localized at the oxygen atoms of the (1 × 4) added row and the methoxy species bonded to the Ti_4C sites, respectively, for the clean and methanol-covered anatase TiO₂(001)-(1 × 4) surfaces. This leads to a Ti_4C site-specific oxidation of the methoxy species by photogenerated holes. These results reveal a concept of surface reconstruction-induced site-specific charge separation and photocatalytic reaction on oxide photocatalysts that will greatly deepen the understanding of the vital role of oxide surface structure in photocatalytic reactions