Issue 24, 2019

Surface phase diagrams of La-based perovskites towards the O-rich limit from first principles

Abstract

The exposed termination of transition-metal oxide surfaces plays a major role in determining the catalyst performance in redox reactions. In this contribution, the surface phase diagrams of LaMO3(001) (M = Sc–Fe) and LaMO3(110) (M = Co–Cu) are constructed by using the DFT+U method. The stabilities of six terminations derived from the stoichiometric MO2 and LaO surfaces are determined over a wide range of temperatures and oxygen partial pressures. The surface phase diagrams are calculated towards the O-rich limit in which the chemical potential of oxygen anions of perovskites equals that of gas-phase oxygen while the chemical potential of M cations is limited by thermodynamic boundary conditions. It is found that the surface phase diagrams are closely related to the reducibility of M cations, which is reflected in the oxygen adsorption energy and oxygen vacancy formation energy on the MO2- and LaO-terminated surfaces and can be measured by the third ionization energies of the M2+ cations. According to the surface phase diagrams, the most stable surface termination is predicted to be of MO2 type for LaMO3 (M = Sc–Fe) and LaO type for LaMO3 (M = Co–Cu) under solid oxide fuel cell operating conditions. Because the M cations become more readily reduced on going from left to right across the period, LaCoO3 may form an oxygen-deficient crystal structure at high temperatures and LaNiO3 and LaCuO3 would be decomposed into oxides containing the transition metals in a lower oxidation state.

Graphical abstract: Surface phase diagrams of La-based perovskites towards the O-rich limit from first principles

Supplementary files

Article information

Article type
Paper
Submitted
23 apr 2019
Accepted
03 jun 2019
First published
03 jun 2019

Phys. Chem. Chem. Phys., 2019,21, 12859-12871

Surface phase diagrams of La-based perovskites towards the O-rich limit from first principles

Y. Li, J. Yang, Y. Zhu, Z. Sui, X. Zhou, D. Chen and W. Yuan, Phys. Chem. Chem. Phys., 2019, 21, 12859 DOI: 10.1039/C9CP02288K

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