Bebensee, Fabian

Moors, Marco

Nefedov, Alexei

Schöttner, Ludger

Wang, Yuemin

Wöll, Christof

Yu, Xiaojuan

English

KITopen

KIT – The Research University in the Helmholtz AssociationInstitute of functional interfaces (IFG), Helmholtz-Research-School „Energy related catalysis“www.kit.eduProbing the surface structure of thin TiOx films on Pt3Ti(111) by IRRAS and XPSLudger Schöttner, Marco Moors, Fabian Bebensee, Xiaojuan Yu, Alexei Nefedov, Yuemin Wang, Christof WöllDPG meeting, Dresden, 21.03.2017IFG, Energy-related-catalysis2OutlineⅠ IntroductionⅡ ExperimentalⅢ Results and DiscussionⅣ ConclusionsProbing the surface structure of thin TiOx films on Pt3Ti(111) by IRRAS and XPS20.03.2017IFG, Energy-related-catalysis3 Probing the surface structure of thin TiOx films on Pt3Ti(111) by IRRAS and XPS20.03.2017H.-J. Freund, J. Am. Chem. Soc. 2016, 138, 8985-8996.Different stereotypes of oxide filmsOxide films exhibit other structural and electronical properties than bulkoxide materials -> metal deposits agglomerate in different mannerChallenge for catalyst modification: Tailoring Selectivity and ReactivityPhysical background often referred with so called strong-metal supportinteractions (SMSI) Oxide films on metallic substrates are attractive candidates for surfacescience studies which bypasses the problem of charging effectsⅠ Oxide films as templates for catalystsIFG, Energy-related-catalysis4Ⅰ Motivation for investigations on Pt3Ti(111) 20.03.2017Electrocatalysis: Electronical structure tuning on Pt-cathodes by auxillary ingredients may lead to improved activites for oxygen reduction reaction (ORR) in polymer electrolyte membrane fuel cells (PEMFC)The (111) facet of Pt possess the lowestsurface energy, ORR reactivePt-Ti alloy crystal allows the facile generation ofthin film structures and avoids the usage ofatomic beam epitaxy from titanium vapormaterial on platinumCertain titanium oxide phases of distinctivemorphology and stoichiometry can besynthesized on Pt3Ti(111) under definedpreparation conditions in high reproducibilityS.Le Moal, M. Moors, J. Essen, C. Breinlich, C. Becker, K. Wandelt, J. Phys. Condens. Mat. 2013, 25, 4, 1-11.J. Greeley, I. Stephens, A. Bondarenko, T. Johansson, H. Hansen, T. Jaramillo, J. Rossmeisl, I. Chorkendorff, J. Norskov, Nat. Chem 2009, 1, 552–556.C. Breinlich, M. Buchholz, M. Moors, S. Le Moal, C. Becker, K. Wandelt, J. Phys. Chem. C 2014, 118, 6186-6192.„Sabatier“ volcanoRect-TiO2z‘-TiO2 w‘-TiO2Probing the surface structure of thin TiOx films on Pt3Ti(111) by IRRAS and XPSIFG, Energy-related-catalysis5Ⅱ UHV-apparatus „THEO“20.03.2017IR-Reflectance absorbance mode for single crystals in grazing incidence (θ=80°)IR-Transmission mode for powder samplesSample cooling to 100 K (LN2) or 60 K (LHe) in IR chamberIntegrated polarizer for s- and p- IR beams allowsorientational studies of molecules deposited on surfacesBasic concept and capacitiesUHV enables adsorption measurements on the low reflective class of metaloxides witha common FT-IR-spectrometerEquipped with XPS, LEED, IR, AES, UPS, TDSSample heating up to 1200 K Ingenious sample transfer systemIR featuresProbing the surface structure of thin TiOx films on Pt3Ti(111) by IRRAS and XPSIFG, Energy-related-catalysis6Ⅱ Strategies and advantages20.03.2017.Probing the surface structure of thin TiOx films on Pt3Ti(111) by IRRAS and XPSSpectroscopical analysis as powerful and versatile tool foroxidation monitoringNot concerned and limited to crystallographic statesCO molecule as probing agent for surface structure changesBoth methods, IRRAS and XPS, can be combined forcomplementary studiesInvestigations on initial stages seems legitIFG, Energy-related-catalysis7Ⅲ Preparation and termination of Pt3Ti(111)20.03.2017Executed sample preparation: 3 kV Ar+ sputtering energy10 minutes, 1100 K annealing 15 minutes. CO probing by IRRAS may confirm defective surfacestructure for Pt-Pt3Ti as recently reported.M. Paßens, V. Caciuc, N. Atodiresei, M. Moors, S. Blügel, R. Waser, S. Karthäuser, Nanoscale 2016, 8, 13924-13933.Severine Le Moal, M. Moors, J. M. Essen, C. Becker, K. Wandelt, Surf. Sci. 2010, 604, 1637-1644.LEED pattern p(2x2) IRRAS: CO on Pt3TiXPS spectra of Pt 4 core level of clean Pt3Ti(111) forgrazing and normal emissionProbing the surface structure of thin TiOx films on Pt3Ti(111) by IRRAS and XPST=130 KIFG, Energy-related-catalysis8Ⅲ Preparation of ordered oxide phases grownon Pt3Ti(111)20.03.2017S.Le Moal, M. Moors, J. Essen, C. Breinlich, C. Becker, K. Wandelt, J. Phys. Condens. Mat. 2013, 25, 4, 1-11.Oxidation between 500-800 K leads to the formation of disordered filmsOrdered oxide phases can be gained between 800-1100 K in dependency of oxygen dosages for partial pressures in p(O2)=10-8-10-5 mbar rangez‘-TiOx (zig-zig-structure) and w‘-TiOx (wagon-wheel) are temperature resistant phases, while incommensurate z-TiOx and rect-TiO2 structures comply metastable criteria as they will be transformed into w‘-TiOx after a harsh postannealing treatmentExperimental phase diagram forO2/Pt3Ti and recorded LEED patterns of obtained oxidesuperstructures:z‘-TiOxw‘-TiOxrect-TiO2z-TiOxOxide-phase Synthesis LEEDz‘-TiOx T = 1000 K150-200 L O210-8 mbar6x3√3w‘-TiOx T = 1000 K500-4000 L O210-7 mbar(7x7)R21.8°z-TiOx T = 800 K900 L O210-6 mbarincommensuraterect-TiO2 T = 800 K4500 L O210-5 mbarincommensurateProbing the surface structure of thin TiOx films on Pt3Ti(111) by IRRAS and XPSIFG, Energy-related-catalysis9Ⅲ XPS studies on ordered TiOx/Pt3Ti(111) films20.03.2017Species Material Binding energy [eV]This workBinding energy[eV]ReferenceTi4+TiOx/Pt3Ti(111)TiOx/Pt(111)TiO2(bulk)458,3 458,0458,4459,0Ti3+TiOx/Pt3Ti(111)TiOx/Pt(111)Ti2O3 (bulk)456,2 456,3456,2457,5Pt2+Pt3Ti(111)Pt Ti PowderTiOx/Pt3Ti(111)Pt/CeO2powder73,072,872,672,8Pt Pt3Ti(111)PtTi PowderPt(111)TiOx/Pt3Ti(111)Pt/CeO2powder71,371,171,571,470,971,1Oxygen on Pt(111) see ref. D. Fantauzzi, S. K. Calderon, J. E. Mueller, M. Grabau, C. Papp, H.-P. Steinrück, T. P. Senftle, A. C. T. van Duin, T. Jacob, Angew. Chem, 2017, 129, 2638-2642.Quantitative XPS see ref. P. Streubel, R. Hesse, L. Makhova, J. Schindelka, R. Denecke, Technical report 2011.𝐼𝐴𝐼𝑆=𝑇𝐴𝜎𝐴𝑛𝐴𝜆𝐴,𝐴𝑇𝑆𝜎𝑆𝑛𝑆𝜆𝑆,𝑆∙1 − 𝑒−𝑑൯𝜆𝐴,𝐴 co s(𝜃𝑒−𝑑൯𝜆𝐴,𝑆 co s(𝜃z‘-TiOx:1,7 Åw‘-TiOx: 2,0 Årect-TiO2:  2,6 ÅLayer thicknessProbing the surface structure of thin TiOx films on Pt3Ti(111) by IRRAS and XPSIFG, Energy-related-catalysis10Ⅲ XPS: Effect of oxygen dosage on thin TiOx film growth20.03.2017TinO2n-1 (2n-1)/nTiOTi2O3Ti3O5Ti4O7Ti5O9Ti6O11Ti7O13Ti8O15Ti9O17Ti10O19TiO21.00001.50001.66671.75001.80001.83331.85711.87501.88891.90002.0000TiO:   -123,9 kcal/molTiO2:  -224,9 kcal/molTi2O3: -363,0 kcal/molTi3O5: -586,7 kcal/molPtO:     -17,0 kcal/molPtO2:    -32,0 kcal/molProbing the surface structure of thin TiOx films on Pt3Ti(111) by IRRAS and XPSIFG, Energy-related-catalysis11Ⅲ IRRAS on oxidized Pt3Ti(111)20.03.2017Pt3Ti(111) + 10 L O2(1000 K)Pt3Ti(111) + 20 L O2(1000 K)Heating experimentCO adsorptionProbing the surface structure of thin TiOx films on Pt3Ti(111) by IRRAS and XPSIFG, Energy-related-catalysis12Ⅲ Discussion20.03.2017CO on Pt (Blyholder-model)5σ CO   => 6sp Pt2π* CO <= 5d Pt„2087 cm-1 “Pt d-band narrowed bysubsurface titanium„2100“ cm-1 in agreement with Pt(111)Pt3Ti(111)+O2 -> TiOx/Pt(111)Probing the surface structure of thin TiOx films on Pt3Ti(111) by IRRAS and XPSIFG, Energy-related-catalysis13Ⅳ Conclusion20.03.2017All common oxide overstructures exist in mixtures of Ti3+/Ti4+ and closethe surface in oxygen terminationLayer thickness calculations let us assume a O-Ti bilayer stacking for z‘ and w‘, but a O-Ti-O trilayer film for rect-TiO2 on a platinum terminatedinterfaceFor low oxidized Pt3Ti(111) (O2 dosage < 20 L) Ti2+ was proposed asintermediate speciesIRRAS data for CO on clean Pt3Ti (111) reveal the complex surfacestructure for alloyed materials including Pt d-band narrowing by Ti-dopingCO adsorption behavior on Pt3Ti(111) quite similar to Pt(111)Surface segregation of titanium during oxidation of Pt3Ti(111) confirmedby CO stretch vibration blueshift from 2087 cm-1 to 2100 cm-1CO induced surface reduction of low oxidized Pt3Ti(111) properlyobserved near desorption temperatureThank you for your attention!Probing the surface structure of thin TiOx films on Pt3Ti(111) by IRRAS and XPS

Probing the surface structure of thin TiOx films on Pt3Ti(111) by IRRAS and XPS

https://publikationen.bibliothek.kit.edu/1000075842/4426773

Probing the surface structure of thin TiOx films on Pt3Ti(111) by IRRAS and XPS

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