A systematic evaluation of the role of lanthanide elements in functional complex oxides; implications for energy conversion devices
File(s)
Published version
Author(s)
Type
Journal Article
Abstract
Lanthanide containing complex oxides, especially the ABO3 perovskite and A(n+1)BnO(3n+1) Ruddlesden–Popper series, attract much interest as promising catalytic materials in many renewable energy applications such as electro-chemical energy conversion and hydrogen production. Recent experimental and theoretical studies on some members of these materials, e.g. La2NiO4, revealed that the La–O terminated surfaces are catalytically active under operational conditions. These findings suggested that the conventional understanding of such oxides being fully ionized, and composed of catalytically inert La3+ ions needs to be revised. In this study, generalized gradient approximation and hybrid density functional theory methods were used to study and compare the electronic structures of La and Sr in related oxides. Density functional theory approaches based on both Gaussian and plane wave basis sets were employed to ensure robustness of this study. Consistent results were obtained across different ab initio methods and approaches used. Density of states plots and charge analysis results showed that La exhibits a partially occupied d-orbital and an atomic charge of +2 instead of its nominal valence number (+3) in the oxides, while Sr does not show similar characteristics. Electron density maps obtained from synchrotron X-ray diffraction experiments confirmed the simulation findings as well. The presence of the available d-orbital electron on La and associated partial covalency were postulated as being responsible for the catalytic behaviour observed in experiments. In addition, Pr and Ba electronic structures in related oxides were also calculated. A similar trend to the La and Sr charges was observed. Based on these findings, the traditional concept of atomic “ionicity” was briefly reviewed and adapted as a catalysis descriptor for possible performance evaluation.
Date Issued
2018-07-07
Date Acceptance
2018-05-16
Citation
Journal of Materials Chemistry A, 2018, 6 (25), pp.11819-11829
ISSN
2050-7488
Publisher
Royal Society of Chemistry
Start Page
11819
End Page
11829
Journal / Book Title
Journal of Materials Chemistry A
Volume
6
Issue
25
Copyright Statement
© The Royal Society of Chemistry 2018. This article is licensed under a Creative Commons Attribution 3.0 Unported Licence (https://creativecommons.org/licenses/by/3.0/)
Sponsor
Engineering & Physical Science Research Council (EPSRC)
Identifier
https://pubs.rsc.org/en/content/articlelanding/2018/TA/C8TA01191E
Grant Number
EP/P026478/1
Subjects
Science & Technology
Physical Sciences
Technology
Chemistry, Physical
Energy & Fuels
Materials Science, Multidisciplinary
Chemistry
Materials Science
INITIO MOLECULAR-DYNAMICS
3-DIMENSIONAL VISUALIZATION
ELECTRONIC-STRUCTURE
POWDER DIFFRACTION
PEROVSKITE OXIDES
CHEMICAL-BOND
SURFACE
OXYGEN
PSEUDOPOTENTIALS
EXCHANGE
0303 Macromolecular and Materials Chemistry
0912 Materials Engineering
0915 Interdisciplinary Engineering
Publication Status
Published
Date Publish Online
2018-05-17