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25.10.2016

 


Improved chemical and electrochemical stability of perovskite oxides with less reducible cations at the surface pp1010 - 1016


Nikolai Tsvetkov, Qiyang Lu, Lixin Sun, Ethan J. Crumlin & Bilge Yildiz


doi:10.1038/nmat4659


The chemical instability of perovskite oxide surfaces limits their energy conversion performance. Significantly enhanced electrochemical stability in a model perovskite electrocatalyst has now been achieved using less reducible cations.


 Nikolai Tsvetkov1,2†, Qiyang Lu1,3†, Lixin Sun1,2, Ethan J. Crumlin4 and Bilge Yildiz1,2,3*


Segregation and phase separation of aliovalent dopants on perovskite oxide (ABO3) surfaces are detrimental to the

performance of energy conversion systems such as solid oxide fuel/electrolysis cells and catalysts for thermochemical H2Oand

CO2 splitting. One key reason behind the instability of perovskite oxide surfaces is the electrostatic attraction of the negatively

charged A-site dopants (for example, Sr0La) by the positively charged oxygen vacancies (Vˆˆ

O ) enriched at the surface. Here we

show that reducing the surface Vˆˆ O concentration improves the oxygen surface exchange kinetics and stability significantly,

albeit contrary to the well-established understanding that surface oxygen vacancies facilitate reactions with O2 molecules.

We take La0.8Sr0.2CoO3 (LSC) as a model perovskite oxide, and modify its surface with additive cations that are more and

less reducible than Co on the B-site of LSC. By using ambient-pressure X-ray absorption and photoelectron spectroscopy, we

proved that the dominant role of the less reducible cations is to suppress the enrichment and phase separation of Sr while

reducing the concentration of VˆˆO and making the LSC more oxidized at its surface. Consequently, we found that these less

reducible cations significantly improve stability, with up to 30 times faster oxygen exchange kinetics after 54 h in air at 530 C

achieved by Hf addition onto LSC. Finally, the results revealed a ‘volcano’ relation between the oxygen exchange kinetics

and the oxygen vacancy formation enthalpy of the binary oxides of the additive cations. This volcano relation highlights the

existence of an optimum surface oxygen vacancy concentration that balances the gain in oxygen exchange kinetics and the

chemical stability loss.

 


 


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А Б В Г Д Е Ё Ж З И Й К Л М Н О П Р С Т У Ф Х Ц Ч Ш Щ Ъ Ы Ь Э Ю Я
  • Chen Wev .  honorary member of ISSC science council

  • Harton Vladislav Vadim  honorary member of ISSC science council

  • Lichtenstain Alexandr Iosif  honorary member of ISSC science council

  • Novikov Dimirtii Leonid  honorary member of ISSC science council

  • Yakushev Mikhail Vasilii  honorary member of ISSC science council

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