TY - JOUR
T1 - A systematic evaluation of the role of lanthanide elements in functional complex oxides; Implications for energy conversion devices
AU - Wu, Ji
AU - Fujii, Kotaro
AU - Yashima, Masatomo
AU - Staykov, Aleksandar
AU - Akbay, Taner
AU - Ishihara, Tatsumi
AU - Kilner, John A.
N1 - Funding Information:
This project was supported by the Japan Society for the Promotion of Science (JSPS) and the National Science Foundation (NSF) under the JSPS-NSF Partnerships for International Research and Education (PIRE), and the Core-to-Core Program on Solid Oxide Interfaces for Faster Ion Transport (SOIFIT) funded by JSPS and EPSRC (grant no. EP/P026478/1). This work was also supported by the World Premier International Research Centre Initiative (WPI), Ministry of Education, Culture, Sports, Science, and Technology of Japan (MEXT). K. F. and M. Y. acknowledge the support by the Grant-in-Aid for Scientic Research (KAKENHI, No. JP15H02291, JP16H06293, JP16K21724, and JP17H06222) from the MEXT, Japan. The synchrotron experiments were carried out at SPring-8 (2017A1803 and 2017B1265).
Funding Information:
This project was supported by the Japan Society for the Promotion of Science (JSPS) and the National Science Foundation (NSF) under the JSPS-NSF Partnerships for International Research and Education (PIRE), and the Core-to-Core Program on Solid Oxide Interfaces for Faster Ion Transport (SOIFIT) funded by JSPS and EPSRC (grant no. EP/P026478/1). This work was also supported by the World Premier International Research Centre Initiative (WPI), Ministry of Education, Culture, Sports, Science, and Technology of Japan (MEXT). K. F. and M. Y. acknowledge the support by the Grant-in-Aid for Scientific Research (KAKENHI, No. JP15H02291, JP16H06293, JP16K21724, and JP17H06222) from the MEXT, Japan. The synchrotron experiments were carried out at SPring-8 (2017A1803 and 2017B1265).
PY - 2018
Y1 - 2018
N2 - 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.
AB - 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.
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U2 - 10.1039/c8ta01191e
DO - 10.1039/c8ta01191e
M3 - Article
AN - SCOPUS:85049124272
VL - 6
SP - 11819
EP - 11829
JO - Journal of Materials Chemistry A
JF - Journal of Materials Chemistry A
SN - 2050-7488
IS - 25
ER -