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The correlation between the structural phase transition (SPT) and oxygen vacancy in SrRuO3 (SRO) thin films was investigated by in situ X-ray diffraction (XRD) and ambient pressure X-ray photoelectron spectroscopy (AP-XPS). In situ XRD shows that the SPT occurs from a monoclinic SRO phase to a tetragonal SRO phase near ∼200 °C, regardless of the pressure environment. On the other hand, significant core level shifts in both the Ru and Sr photoemission spectra are found under ultrahigh vacuum, but not under the oxygen pressure environment. The directions and behavior of the core level shift of Ru and Sr are attributed to the formation of oxygen vacancy across the SPT temperature of SRO. The analysis of in situ XRD and AP-XPS results provides an evidence for the formation of metastable surface oxide possibly due to the migration of internal oxygen atoms across the SPT temperature, indicating the close relationship between oxygen vacancy and SPT in SRO thin films.

The surface chemical states of Pd(100) during CO oxidation were investigated using ambient pressure x-ray photoelectron spectroscopy and mass spectroscopy. Under the reactant ratio of CO/O 2 = 0.1, i.e. an oxygen-rich reaction condition, the formation of surface oxides was observed with the onset of CO oxidation reaction at T = 525 K. As the reactant ratio (CO/O 2 ) increased from 0.1 to 1.0, ∼ 90 % surface oxides remains on surface during the reaction. Upon the formation of surface oxides, the core level shift of oxygen gas phase peak was observed, indicating that change of surface work function. As CO oxidation takes places, i.e. making a transition from CO covered surface to the oxidic surface, the work functions of surface oxide on Pd(100) and Pt(110) display opposite behavior.

The study of CO oxidation on Pt(110) surface is revisited using ambient pressure x-ray photoemission spectroscopy. When the surface temperature reaches the activation temperature for CO oxidation under elevated pressure condition, both the -phase of PtO2 oxide and chemisorbed oxygen are formed simultaneously on the surface. Due to exothermic nature of CO oxidation, the temperature of Pt surface increases as CO oxidation takes places. As the CO/O2 ratio increases, the production of CO2 increases continuously and the surface temperature also increases. Interestingly, during the mass transfer limiting regions, the amount of surface oxide changes little while the chemisorbed oxygen is being reduced. .

The study of CO oxidation on Pt(110) surface is revisited using ambient pressure x-ray photoemission spectroscopy. When the surface temperature reaches the activation temperature for CO oxidation under elevated pressure condition, both the -phase of PtO2 oxide and chemisorbed oxygen are formed simultaneously on the surface. Due to exothermic nature of CO oxidation, the temperature of Pt surface increases as CO oxidation takes places. As the CO/O2 ratio increases, the production of CO2 increases continuously and the surface temperature also increases. Interestingly, during the mass transfer limiting regions, the amount of surface oxide changes little while the chemisorbed oxygen is being reduced. .

With synchrotron-based depth-resolved XPS measurements, the modification of the surface chemical states and the behavior of various impurities on undoped SrTiO3(001) surfaces are investigated. During the Ar+ sputtering process, both the formation of oxygen vacancies in the TiO2 layer and the formation of the SrO layer are found. When the UHV annealing process starts, the oxygen vacancies in the TiO2 layer start to decrease, indicating oxygen migration from the bulk to the surface region. In the annealing step at 873 K, the concentration of the oxygen vacancies starts to increase due to the lattice oxygen loss to a UHV atmosphere. Throughout the surface preparation process, the sample impurities always exist on the surface with a small variation in their chemical states. The variation of the chemical states of SrTiO3 and its impurities is an indication of the oxygen exchange during the sample preparation process. Our results provide valuable insights on how the elements of SrTiO3 behave during the surface preparation process and interact with surface impurities. [ABSTRACT FROM AUTHOR]

In this study, we performed the CO2 reduction reaction (CO2RR) using a structural composite catalyst of cuprous oxide (Cu2O) and silver (Ag) that was simultaneously electrodeposited. While the underneath Ag electrodeposits maintained their spiky backbone structures even after the CO2RR, the Cu2O deposits were reduced to Cu(111) and relocated on the backbone template. The structural changes in Cu2O to Cu increase the active area of the Cu–Ag interface, resulting in a remarkable production rate of 125.01 μmol h−1 of liquid C2+ chemicals via the stabilization of the C–C coupling of the key intermediate species of acetaldehyde. This study provides new insights into designing a bimetallic catalyst for producing sustainable C2+ products from CO2 without any selectivity towards the production of methane. [ABSTRACT FROM AUTHOR]

SrTiO3, an ABO3-type perovskite structure, has been a popular choice of substrate for many important heterostructures, e.g., ferroelectric thin films and superlattices. As numerous exotic physical phenomena are closely related to delicate electron/ion exchanges at the interfacial layer between the substrate and overlayer, precise characterization of surface/interfacial properties has become the center of many research studies. In most cases of SrTiO3 research, Nb-doping is applied on the SrTiO3 surface in order to characterize electrical properties with a negligible effect of contact potential between SrTiO3 and overlayer. On the other hand, the presence of doping can possibly interfere with a correct interpretation of the surface defect states, which become critical to apprehend the electrical properties of heterostructures. In this report, the undoped SrTiO3 (001) surface is investigated utilizing ambient-pressure XPS (AP-XPS) and low energy electron diffraction (LEED). We identified the complete chemical/structural/electronic states of O and Sr vacancies on the undoped SrTiO3 surface from ultra-high vacuum (UHV, <10−9 mbar) to O2 gas pressure of 0.1 mbar conditions. Under oxygen pressure conditions, chemically stable SrO1+x surface oxide with a c(6 × 2) superstructure is formed, generating electron depletion and band bending, i.e., the formation of a space charge layer underneath the surface. On the other hand, under UHV, the surface oxide comes from the O vacancy, which has different electronic properties from those of Sr vacancy-related oxides. [ABSTRACT FROM AUTHOR]

Utilizing ambient pressure x-ray photoelectron spectroscopy, the surface segregation and the oxidation dynamics of platinum (Pt)-3d transition metal (M) alloys, Pt3M (M = Ti, V), are investigated. Under oxygen-rich conditions, i.e., P(CO)/P(O2) = 0.1, Pt3V surface forms Pt skin layer while Pt3Ti shows the presence of both Ti and Pt atoms. As temperature increases to 450 K, V atoms make surface segregation to form oxide while Ti atoms start to form various Ti oxides (Ti2O3 and TiOx) on the surface. When CO oxidation occurs at 600 K, the oxidation continues on both surfaces of Pt3M (M = Ti, V), showing the enhancement of TiOx for Pt3Ti and V2O5 and VOx for Pt3V. Also, during CO oxidation, a sign of pure metallic Pt state is found at Pt 4f spectra in both surfaces, suggesting the redistribution of electrons from the transition metals during the oxide formation. [ABSTRACT FROM AUTHOR]

In this study, we performed the CO2 reduction reaction (CO2RR) using a structural composite catalyst of cuprous oxide (Cu2O) and silver (Ag) that was simultaneously electrodeposited. While the underneath Ag electrodeposits maintained their spiky backbone structures even after the CO2RR, the Cu2O deposits were reduced to Cu(111) and relocated on the backbone template. The structural changes in Cu2O to Cu increase the active area of the Cu–Ag interface, resulting in a remarkable production rate of 125.01 μmol h−1 of liquid C2+ chemicals via the stabilization of the C–C coupling of the key intermediate species of acetaldehyde. This study provides new insights into designing a bimetallic catalyst for producing sustainable C2+ products from CO2 without any selectivity towards the production of methane. [ABSTRACT FROM AUTHOR]

The adsorption properties of CO 2 on the SrTiO 3 (001) surface were investigated using ambient pressure X-ray photoelectron spectroscopy under elevated pressure and temperature conditions. On the Nb-doped TiO 2 -enriched (1 × 1) SrTiO 3 surface, CO 2 adsorption, i.e., the formation of CO 3 surface species, occurs first at the oxygen lattice site under 10 -6 mbar CO 2 at room temperature. The interaction of CO 2 molecules with oxygen vacancies begins when the CO 2 pressure increases to 0.25 mbar. The adsorbed CO 3 species on the Nb-doped SrTiO 3 surface increases continuously as the pressure increases but starts to leave the surface as the surface temperature increases, which occurs at approximately 373 K on the defect-free surface. On the undoped TiO 2 -enriched (1 × 1) SrTiO 3 surface, CO 2 adsorption also occurs first at the lattice oxygen sites. Both the doped and undoped SrTiO 3 surfaces exhibit an enhancement of the CO 3 species with the presence of oxygen vacancies, thus indicating the important role of oxygen vacancies in CO 2 dissociation. When OH species are removed from the undoped SrTiO 3 surface, the CO 3 species begin to form under 10 -6 mbar at 573 K, thus indicating the critical role of OH in preventing CO 2 adsorption. The observed CO 2 adsorption properties of the various SrTiO 3 surfaces provide valuable information for designing SrTiO 3 -based CO 2 catalysts.

In this study, we performed the CO 2 reduction reaction (CO 2 RR) using a structural composite catalyst of cuprous oxide (Cu 2 O) and silver (Ag) that was simultaneously electrodeposited. While the underneath Ag electrodeposits maintained their spiky backbone structures even after the CO 2 RR, the Cu 2 O deposits were reduced to Cu(111) and relocated on the backbone template. The structural changes in Cu 2 O to Cu increase the active area of the Cu-Ag interface, resulting in a remarkable production rate of 125.01 μmol h -1 of liquid C 2+ chemicals via the stabilization of the C-C coupling of the key intermediate species of acetaldehyde. This study provides new insights into designing a bimetallic catalyst for producing sustainable C 2+ products from CO 2 without any selectivity towards the production of methane.

Cesium oxide (CsO x ) nanostructures grown on Au(111) behave as active centers for the CO 2 binding and hydrogenation reactions. The morphology and reactivity of these CsO x systems were investigated as a function of alkali coverage using scanning tunneling microscopy (STM), ambient pressure X-ray photoelectron spectroscopy (AP-XPS), and density functional theory (DFT) calculations. STM results show that initially (0.05-0.10 ML) cesium oxide clusters (Cs 2 O 2 ) grow at the elbow sites of the herringbone of Au(111), subsequently transforming into two-dimensional islands with increasing cesium coverage (>0.15 ML). XPS measurements reveal the presence of suboxidic (Cs y O; y ≥ 2) species for the island structures. The higher coverages of cesium oxide nanostructures contain a lower O/Cs ratio, resulting in a stronger binding of CO 2 . Moreover, the O atoms in the Cs y O structure undergo a rearrangement upon the adsorption of CO 2 which is a reversible phenomenon. Under CO 2 hydrogenation conditions, the small Cs 2 O 2 clusters are hydroxylated, thereby preventing the adsorption of CO 2 . However, the hydroxylation of the higher coverages of Cs y O did not prevent CO 2 adsorption, and adsorbed CO 2 transformed to HCOO species that eventually yield HCOOH. DFT calculations further confirm that the dissociated H 2 attacks the C in the adsorbate to produce formate, which is both thermodynamically and kinetically favored during the CO 2 reaction with hydroxylated Cs y O. These results demonstrate that cesium oxide by itself is an excellent catalyst for CO 2 hydrogenation that could produce formate, an important intermediate for the generation of value-added species. The role of the alkali oxide nanostructures as active centers, not merely as promoters, may have broad implications, wherein the alkali oxides can be considered in the design of materials tuned for specific applications in heterogeneous catalysis.

The correlation between the structural phase transition (SPT) and oxygen vacancy in SrRuO 3 (SRO) thin films was investigated by in situ X-ray diffraction (XRD) and ambient pressure X-ray photoelectron spectroscopy (AP-XPS). In situ XRD shows that the SPT occurs from a monoclinic SRO phase to a tetragonal SRO phase near ∼200 °C, regardless of the pressure environment. On the other hand, significant core level shifts in both the Ru and Sr photoemission spectra are found under ultrahigh vacuum, but not under the oxygen pressure environment. The directions and behavior of the core level shift of Ru and Sr are attributed to the formation of oxygen vacancy across the SPT temperature of SRO. The analysis of in situ XRD and AP-XPS results provides an evidence for the formation of metastable surface oxide possibly due to the migration of internal oxygen atoms across the SPT temperature, indicating the close relationship between oxygen vacancy and SPT in SRO thin films.