Identification of surface composition and chemical states in composites comprised of phases with fluorite and perovskite structures by X-ray photoelectron spectroscopy

Abstract

Keywords:X-ray photoelectron spectroscopy (XPS) Surface composition Composites with perovskite and fluorite structures Oxidation state of cerium cations Binding energy a b s t r a c t X-ray photoelectron spectroscopy (XPS) has been used to explore the cation rearrangement between the surface and bulk of grains and the surface chemical states of Ce, Mn, Co, Sr, and O ions in the single phase CeO 2 -based solid solutions and in the two phase (100 − x)La 0.6 Sr 0.4 CoO 3 -xCeO 2 (LSCCx) and (100 − x)La 0.8 Sr 0.2 MnO 3 -xCeO 2 (LSMCx) composites. The well-resolved Ce 3d 5/2 and Ce 3d 3/2 spin-orbit components were determined to study the Ce 4+ to Ce 3+ electronic transition at the surface. The surface of the LSCCx and LSMCx (x = 8-40 mol%) composites is depleted in cerium. Both Ce 4+ and Ce 3+ cations were revealed. The surface fraction of Ce 4+ cations increases with the rise in CeO 2 content in both systems, but it is higher by about a factor of two in the LSCC composites. A strong enrichment of the surface by Co cations was observed for the composites LSCCx (x = 8-40 mol%), implying that the presence of cerium could facilitate the Co surface segregation. A slight Sr surface enrichment compared to the nominal stoichiometry was found for La 0.6 Sr 0.4 CoO 3 , CeO 2 -based solid solutions, LSCC57, and LSMCx (x = 10-57) composites. In contrast, the surface of the LSCCx (x = 10-37) composites is slightly depleted in strontium cations. The O 1s spectra of the LSCC and LSMC composites contain several contributions associated with the lattice oxygen related to the phases with the perovskite and fluorite structures as well as with different surface states. Their contributions vary with CeO 2 content and a chemical origin of the transition metal cations on the B-site in the perovskite structure. The Ce 2 (CO 3 ) 3 -based phase seems to exist at the surface of grains and crystallites in the LSCC57 and LSCM composites.

Nano-CeO2-Modified Cathodes for Direct Electrochemical CO2 Reduction in Solid Oxide Electrolysis Cells

“…To investigate the surface chemical states of the cathodes, the LSCM-GDC and 3 wt %-CeO 2 -LSCM-GDC cathodes were reduced at 800 °C in 5% H 2 /Ar and then were examined by X-ray photoelectron spectroscopy (XPS), as shown in Figure . According to reports in the literatures, − the two cathodes show three peaks in the XPS spectra of O 1s (Figure a) corresponding to the lattice oxygen in perovskite (528.6 eV, O L,P ), the lattice oxygen in fluorite (529.5 eV for the reduced LSCM-GDC cathode, 529.3 eV for the reduced 3 wt % CeO 2 -LSCM-GDC cathode, O L,F ), and the adsorbed O–Ce surface species (∼531.2 eV for the reduced LSCM-GDC cathode, 531.0 eV for the reduced 3 wt % CeO 2 -LSCM-GDC cathode, O ads ). Then, the relative atomic concentrations of each oxygen state from the fitting curves are estimated as shown in Table .…”

Synthesis and characterization of mixed conductor CeNbO4

“…One doublet (884.8 and 903.7 eV) is characterized by the presence on Ce 3+ state and corresponds to the Ce (3d 9 4f 1 )O(2p 6 ) state [21]. The other doublet (881.4 eV and 899.4 eV) corresponds to Ce (3d 9 4f 2 )O(2p 5 ) state and is a shakedown feature involving electron transfer from a filled O2p orbital to a Ce 4f orbital during photoemission from Ce 3+ cations [23,27]. The XPS results indicate the existence of both Ce 3+ and Ce 4+ cations in the quenched CeNbO 4 sample.…”

“…The complexity of the XPS spectra of the Ce3d is due to multielectric processes both in the Ce 4+ and Ce 3+ states and originates from the hybridization between the Ce4f levels and the O2p states [20,21]. The fitted peaks at 897.5 eV and 916 eV correspond to Ce (3d 9 4f 0 )O(2p 6 ) states of Ce 4+ and the peak 916 eV is normally taken as an indication to detect the presence of the Ce 4+ [22][23][24]. According to the literature [25,26], Ce 3+ oxide is characterized by two pairs of spin-orbit split doublet with two peaks.…”

Formation and characterisation of zirconium-based conversion coating on steel

“…When oxygen is in the form of OH groups, the binding energy is shifted to higher values (532 eV) and when it is present as an oxide, the peak is situated at the lower binding energies (530 eV). [16][17][18] The peak of O 1s at 529.8 eV corresponds to lattice oxygen of zirconia or iron oxide, and a higher binding energy of 531.6 eV is assigned to contributions from zirconium hydroxides or iron hydroxides. The highest binding energy of 534 is attributed to H 2 O in the nano-composite.…”