In Situ XPS Studies of Perovskite Oxide Surfaces under Electrochemical Polarization

Abstract

An in situ XPS study of oxidation-reduction processes on three perovskite oxide electrode surfaces was carried out by incorporating the materials in an electrochemical cell mounted on a heated sample stage in an ultrahigh vacuum (UHV) chamber. Electrodes made of powdered LaCr(1-x)Ni(x)O(3-delta) (x = 0.4, 1) showed changes in the XPS features of all elements upon redox cycling between formal Ni3+ and Ni2+ oxidation stoichiometries, indicating the delocalized nature of the electronic states involved and strong mixing of O 2p to Ni 3d levels to form band states. The surface also showed changes in adsorption capacity for CO2 upon reduction as a result of increased nucleophilicity of surface oxygen. Another perovskite oxide, La(0.5)Sr(0.5)CoO(3-delta), laser deposited as highly oriented thin films on (100) oriented yttria-stabilized zirconia (YSZ), also showed evidence of both local and nonlocal effects in the XPS features upon redox cycling. In contrast to LaCr(1-x)Ni(x)O(3-delta), redox cycling mainly affected the XPS features of cobalt with little effect on oxygen. This signifies reduced participation of O 2p states in the conduction band of this material. Small changes in surface cation stoichiometry in this film were observed and attributed to mobility of the A-site Sr dopant under polarization.

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

“…One could extract a small shoulder on the high binding energy side of the Co 2p 3/2 spectrum. A comparison of the XPS spectra (including shake-up features) reported in the literature for La 1−x Sr x CoO 3±ı , SrCo 4+ O 3 , Co oxides and hydroxides [36,39,[62][63][64][65][66] implies that a small peak at 782.6 eV could be related to the presence of Co 4+ cations. This correlates with the result of the thermal gravimetric analysis showing the average oxidation state of Co cations in the LSC as +3.4 [39].…”

High Redox Capacity of Al‐Doped La1−xSrxMnO3−δ Perovskites for Splitting CO2 and H2O at Mn‐Enriched Surfaces

“…[14] Formation of surfacecarbonates Formation of surfacec arbonates by am etal oxide redox material in contact with the CO 2 oxidanto fasolar fuel production cycle is undesirable since the carbonates block redox-active surfaces ites and, in turn, diminish the redoxp erformance and chemicals tability of the metal oxide.A lkaline-earth metals, like Sr and Ca, may readily form carbonates;t herefore, the following discussion quantifies the extent of carbonate formation at perovskite surfaces. [44,[57][58][59][60] The Ca 2p peak was deconvoluted into two sets of 2p 3/2 and2 p 1/2 signals by fixing the ratio between the areaso ft he 2p 3/2 and 2p g signals to 0.5, as described previously. The spectra for LSMA8282, LSMA8228, LSMA2882, and LCMA6464 are given in the Supporting Information (cf.…”

Microstructure and transport properties of sol–gel derived highly (100)-oriented lanthanum nickel oxide thin films on SiO2/Si substrate

“…Then, to quantitatively distinguish valences state of Ni and to confirm the ratio of Ni 3 þ /Ni 2 þ are of great significance for understanding the electronic transport properties of the films. XPS is deemed as an effective approach to distinguish Ni 3 þ and Ni 2 þ in LNO films [22,23]. Due to the overlapping of Ni 2p 3/2 and La 3d 3/2 peaks, Ni 3p peaks were chosen to determine the ratio of Ni 3 þ /Ni 2 þ , as described by Qiao and Bi [24].…”