The interaction of molecular oxygen on LaO terminated surfaces of La₂NiO₄

Abstract

Rare-earth metal oxides with perovskite-type crystal structures are under consideration for use as air electrode materials for intermediate to high temperature electrochemical device applications.The surface chemistry of these materials plays a critical role in determining the kinetics of oxygen reduction and exchange reactions. Among various perovskite-structured oxides, certain members of the Ruddlesden-Popper series, e.g. La2NiO4, have been identified as significantly active for surface oxygen interaction. However, the challenge remains to be the identification of the structure and composition of active surfaces, as well as the influence of these factors on the mechanisms of surface exchange reactions. In this contribution, the changes in electronic structure and the energetics of oxygen interaction on surfaces of La2NiO4 are analysed using first principle calculations in the Density Functional Theory (DFT) formalism. As for the surface chemistry, the LaO termination rather than the NiO2 is presumed due to recent experimental evidence for the surfaces of various perovskite structured oxides after heat treatment in oxidizing environments being transition metal free. Our findings substantiate that the LaO terminated surface can indeed participate in the formation of the surface superoxo species. Detailed charge transfer analyses revealed that it is possible for such a surface to be catalytically active owing to the enhanced electronic configurations on neighbouring La sites to surface species. In addition, positively charged oxygen vacancies, relative to the crystal lattice, can act as active sites and catalyse the O-O bond cleavage.

Polar or not polar? The interplay between reconstruction, Sr enrichment, and reduction at the La0.75Sr0.25MnO3 (001) surface

“…Since the partial SrO termination is expected to dominate the surface under SOFC operating conditions, we examine its possible relevance in the oxygen reduction reaction. For assessing the catalytic activity of SOFC cathodes in the oxygen reduction reaction (ORR), several different factors play a role, such as the coverage of adsorbed oxygen and its dissociation barrier, but also the oxygen vacancy concentration near the surface and the mobility of these vacancies [17,29,[34][35][36]. While we have not studied these aspects yet in detail for our proposed partial MnO 2 /LaO/SrO terminations, we would like to point out that such terminations may have special properties in the context of the ORR, based on the results of previous studies of Merkle et al [33] and Mastrivkov et al [29].…”

Interaction of SrO-terminated SrTiO3 surface with oxygen, carbon dioxide, and water

“…23 This is especially true for perovskite lattices with alkaline and earth alkaline metals on the A-site, e.g., Sr, Ba, etc., while different catalytic mechanism based on d-electron occupancy was proposed for perovskites with rare earth elements on the A-site, e.g., La, Pr, etc. 24 The electronic properties in the vicinity of surface oxygen vacancies of SrTiO 3 have shown that those vacancies are not simply spatial voids but are regions in space characterized with high electron density. 20 As the molecular oxygen activation and dissociation in an electrophilic reaction, surface oxygen vacancies would be the preferred surface active sites.…”

Surface termination effects on the oxygen reduction reaction rate at fuel cell cathodes

“…5a), in agreement with hybrid LCAO calculations, 55 plane wave GGA calculations 19 and atomic O adsorption on the LaO termination of La 2 NiO 4 . 56 The adsorption energy depends strongly on the Mn oxidation state (see Fig. 7a below) and can reach À4.3 eV.…”