Metal-support interactions at the Pt/Co3O4(111) interface yield Ptδ+ species which control the stability of the supported nanoparticles.

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Iridium-based materials are among the most active bifunctional catalysts in heterogeneous catalysis and electrocatalysis. We have investigated the properties of atomically defined Ir/CeO2(111) model systems supported on Cu(111) and Ru(0001) by means of synchrotron radiation photoelectron spectroscopy, resonant photoemission spectroscopy, near ambient pressure X-ray photoelectron spectroscopy (NAP XPS), scanning tunneling microscopy, and temperature programmed desorption. Electronic metal-support interactions in the Ir/CeO2(111) system are accompanied by charge transfer and partial reduction of CeO2(111). The magnitude of the charge transfer depends strongly on the Ir coverage. The Ir/CeO2(111) system is stable against sintering upon annealing to 600 K in ultrahigh vacuum (UHV). Annealing of Ir/CeO2(111) in UHV triggers the reverse oxygen spillover above 450 K. The interaction of hydrogen with Ir/CeO2(111) involves hydrogen spillover and reversible spillover between 100 and 400 K accompanied by the formation of water above 190 K. Formation of water coupled with the strong reduction of CeO2(111) represents the dominant reaction channel upon annealing in H2 above 450 K. The interaction of Ir/CeO2(111) with oxygen has been investigated at moderate and NAP conditions. Additionally, the formation and stability of iridium oxide prepared by deposition of Ir in oxygen atmosphere was investigated upon annealing in UHV and under exposure to H2. The oxidation of Ir nanoparticles under NAP conditions yields stable IrOx nanoparticles. The stability of Ir and IrOx nanoparticles under oxidizing conditions is hampered, however, by encapsulation by cerium oxide above 450 K and additionally by copper and ruthenium oxides under NAP conditions.

in the materials science community. [2] Apart from the generation of H 2 and O 2 gases, photocatalysis can be extended to other applications. The early works on the irradiation of TiO 2 for purification of water via photocatalytic decomposition of pollutants were demonstrated by Frank and Bard in late 1970s. [3][4][5] These initial works and many reports later have shown that photooxidation of inorganic and organic contaminants is a promising route for environmental remediation. [6][7][8][9][10][11][12] In fact, the key factors that determine the efficiencies of a photocatalyst include its light harvesting capability and reduced charge carriers recombination of the photo generated electron-hole pairs. [3,13] However, TiO 2 possesses rather wide bandgap energies between 3.0 and 3.2 eV, with high photo activity only in the UV region (λ ≤ 390 nm) equivalent to only ≈5% of the solar spectrum. [14,15] Nevertheless, owing to its nontoxicity, low-cost synthesis, chemical inertness, and resistance against photocorrosion, TiO 2 has been long studied and recognized as the most promising photocatalyst material. [13,16] In order to harness more from the abundant renewable energy source, that is, solar energy, tremendous efforts have been devoted to reduce the bandgap energy of TiO 2 and broaden its optical absorption to the visible region. [8,[13][14][15]17,18] Bandgap engineering has been extensively carried out Ultrathin molybdenum oxyselenide (MoSe x O y ) coatings are made first ever by atomic layer deposition (ALD) within anodic 1D TiO 2 nanotube layers for photoelectrochemical and photocatalytic applications. The coating thickness is controlled through varying ALD cycles from 5 to 50 cycles (corresponding to ≈1-10 nm). In the ultraviolet region, the coatings have enhanced up to four times the incident photon-to-current conversion efficiency (IPCE), and the highest IPCE is recorded at 32% at (at λ = 365 nm). The coatings notably extend the photoresponse to the visible spectral region and remarkable improvement of photocurrent densities up to ≈40 times is registered at λ = 470 nm. As a result, the MoSe x O y -coated-TiO 2 nanotube layers have shown to be an effective photocatalyst for methylene blue degradation, and the optimal performance is credited to a coating thickness between 2 and 5 nm (feasible only by ALD). The enhancement in photoactivities of the presented heterojunction is mainly associated with the passivation effect of MoSe x O y on the TiO 2 nanotube walls and the suitability of bandgap position between MoSe x O y and TiO 2 interface for an efficient charge transfer. In addition, MoSe x O y possesses a narrow bandgap, which favors the photoactivity in the visible spectral region.

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