Nature of oxygen at rocksalt and spinel oxide surfaces

Abstract

The chemical environment of oxygen in cobalt-containing metal oxides with compositions͑M,MЈϭMn,Ni,Co͒ has been studied by Auger, x-ray and ultraviolet photoelectron, and high resolution electron energy loss spectroscopies. While there is a single type of lattice oxygen in the bulk structure of simple rocksalt and spinel oxides, the nature of oxygen at the surface of the spinel oxides is considerably more complex. Photoemission from core oxygen states in these materials often shows multiple peaks and satellite structure which have been attributed to a range of intrinsic and extrinsic oxygen states. All of these 3d transition metal oxides show a single, intense O 1s core photoemission peak at approximately 529.6 eV. In the spinel materials, a second state at 531.2 eV is also observed and is shown to be intrinsic to the spinel surface and not a result of hydroxylation or other surface contaminant. Similar photoemission features in Fe 3 O 4 were previously attributed to final state effects; however, the nature of the multiple final states remains to be elucidated.

Surface properties of LiCoO2, LiNiO2 and LiNi1−xCoxO2

“…X-ray photoemission (XPS) from C 1s and O 1s spectral regions showed carbonate to be detectable by XPS for some, although not all, of the samples studied, as will be described in detail below. poses and have been obtained on well-defi ned single crystal substrates [45], [46] and [47]. The Co 2p spectra of the lithium-containing oxides are characteristic of Co 3+ in an octahedral or near-octahedral environment, as is also observed for the spinel Co 3 O 4 structure.…”

“…At 529.2 eV, the value for the LiCoO 2 sample is equal to or only slightly lower than that reported for lattice oxygen in Co 3 O 4 (529.2-529.5 eV; refs. [53], [54], [55] and [56]), and slightly lower than that for CoO (529.4-529.6 eV; refs. [53], [55], [56], [57] and [58]).…”

“…[53], [54], [55] and [56]), and slightly lower than that for CoO (529.4-529.6 eV; refs. [53], [55], [56], [57] and [58]). Furthermore, doping cobalt oxide powders with lithium for up to 50% of the total metal concentration does not appear to change the O 1s binding energy signifi cantly [54].…”

A comparative in situ XPS study of PtRuCo catalyst in methanol steam reforming and water gas shift reactions

“…Depth dependent measurements using higher photon energies (see also below) indicated that the peak at 530.3 eV is to a large extent due to sub-surface species. However the position of this peak is shifted about 0.8 eV as compared to that of the lattice oxygen peak of CoO and Co 3 O 4 oxides (at 529.5 ± 0.2 eV), reported in the literature [30] and measured on reference compounds in the same set-up [31]. The interpretation of 530.3 eV peak will be given below in combination with other results.…”

“…Cobalt (Fig. 2c) is mainly in the oxide form under WGS reaction conditions, as indicated by the BE position of the main peak at 780.4 eV and the intense satellite structure at the high BE side [29] and [30]. Comparison with reference a CoO spectrum reveals an extra bump to the low BE side of the peak (indicated by an arrow).…”