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 + FeCUS + FeO → FeCUS–OwH + FeOH in which Ow 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–Ovacancy + FeO → FeOwH + FeOH and H2O + 2 Fe–Ovacancy → FeOwH + H(a)–Fe–Ovacancy. 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.