Cobalt spinel at various redox conditions : DFT+U investigations into the structure and surface thermodynamics of the (100) facet

2015
journal article
article
59
cris.lastimport.wos2024-04-09T20:57:38Z
dc.abstract.enPeriodic spin unrestricted DFT-PW91+U calculations together with ab initio thermodynamic modeling were used to study the structure, defects, and stability of different terminations of the (100) surface of cobalt spinel under various redox conditions imposed by different oxygen partial pressure and temperature. Three terminations containing under-stoichiometric (100)-O, stoichiometric (100)-S, and overstoichiometric (100)-R amount of cobalt ions were analyzed, and their atomic and defect structure, reconstruction, and stability were elucidated. For the most stable (100)-S and (100)-O facets, formation of cationic and anionic vacancies was examined, and a surface redox state diagram of possible spinel (100) terminations in the stoichiometry range from $Co_{2.25}O_{4}$ to $Co_{3}O_{3.75}$ was constructed and discussed in detail. The results revealed that the bare (100)-S surface is the most stable at temperatures and pressures of typical catalytic processes (T ∼ $200^{o}\textrm{C}$ to ∼$500^{o}\textrm{C} $, $p_{O2}/p^{o}$∼ 0.001 to ∼1). In more reducing conditions (T > $600^{o}\textrm{C}$ and $p_{O2}/p^{o}$ < 0.0001), the (100)-S facet is readily reduced by formation of oxygen vacancies, whereas in the oxidizing conditions (T < $200 ^{o}\textrm{C}$ and $p_{O2}/p^{o}$ > 10), coexistence of (100)-S and (100)-O terminations was revealed. Formation of the oxygen vacancies involves reduction of the octahedral trivalent cobalt and is accompanied by migration of the divalent tetrahedral cobalt into empty, interstitial octahedral positions. It was also found that the constituent octahedral Co cation proximal to the interstitial cobalt adopts a low spin configuration in contrast to the distal one that preserves its surface high spin state. In the case of the Co depleted surfaces, the octahedral vacancies are thermodynamically disfavored with respect to the tetrahedral ones in the whole range of the examined T and $p_{O2}$ values. The obtained theoretical results, supported by $TPD-O_{2}$ and TG experiments, show that the octahedral cobalt ions are directly involved in the redox processes of $Co_{3}O_{4}$.pl
dc.affiliationWydział Chemii : Zakład Chemii Nieorganicznejpl
dc.contributor.authorZasada, Filip - 200610 pl
dc.contributor.authorPiskorz, Witold - 131426 pl
dc.contributor.authorSojka, Zbigniew - 131982 pl
dc.date.accessioned2015-12-02T13:48:14Z
dc.date.available2015-12-02T13:48:14Z
dc.date.issued2015pl
dc.description.number33pl
dc.description.physical19180-19191pl
dc.description.volume119pl
dc.identifier.doi10.1021/acs.jpcc.5b05136pl
dc.identifier.eissn1932-7455pl
dc.identifier.issn1932-7447pl
dc.identifier.urihttp://ruj.uj.edu.pl/xmlui/handle/item/17433
dc.languageengpl
dc.language.containerengpl
dc.rights.licencebez licencji
dc.subtypeArticlepl
dc.titleCobalt spinel at various redox conditions : DFT+U investigations into the structure and surface thermodynamics of the (100) facetpl
dc.title.journalThe Journal of Physical Chemistry. Cpl
dc.typeJournalArticlepl
dspace.entity.typePublication
cris.lastimport.wos
2024-04-09T20:57:38Z
dc.abstract.enpl
Periodic spin unrestricted DFT-PW91+U calculations together with ab initio thermodynamic modeling were used to study the structure, defects, and stability of different terminations of the (100) surface of cobalt spinel under various redox conditions imposed by different oxygen partial pressure and temperature. Three terminations containing under-stoichiometric (100)-O, stoichiometric (100)-S, and overstoichiometric (100)-R amount of cobalt ions were analyzed, and their atomic and defect structure, reconstruction, and stability were elucidated. For the most stable (100)-S and (100)-O facets, formation of cationic and anionic vacancies was examined, and a surface redox state diagram of possible spinel (100) terminations in the stoichiometry range from $Co_{2.25}O_{4}$ to $Co_{3}O_{3.75}$ was constructed and discussed in detail. The results revealed that the bare (100)-S surface is the most stable at temperatures and pressures of typical catalytic processes (T ∼ $200^{o}\textrm{C}$ to ∼$500^{o}\textrm{C} $, $p_{O2}/p^{o}$∼ 0.001 to ∼1). In more reducing conditions (T > $600^{o}\textrm{C}$ and $p_{O2}/p^{o}$ < 0.0001), the (100)-S facet is readily reduced by formation of oxygen vacancies, whereas in the oxidizing conditions (T < $200 ^{o}\textrm{C}$ and $p_{O2}/p^{o}$ > 10), coexistence of (100)-S and (100)-O terminations was revealed. Formation of the oxygen vacancies involves reduction of the octahedral trivalent cobalt and is accompanied by migration of the divalent tetrahedral cobalt into empty, interstitial octahedral positions. It was also found that the constituent octahedral Co cation proximal to the interstitial cobalt adopts a low spin configuration in contrast to the distal one that preserves its surface high spin state. In the case of the Co depleted surfaces, the octahedral vacancies are thermodynamically disfavored with respect to the tetrahedral ones in the whole range of the examined T and $p_{O2}$ values. The obtained theoretical results, supported by $TPD-O_{2}$ and TG experiments, show that the octahedral cobalt ions are directly involved in the redox processes of $Co_{3}O_{4}$.
dc.affiliationpl
Wydział Chemii : Zakład Chemii Nieorganicznej
dc.contributor.authorpl
Zasada, Filip - 200610
dc.contributor.authorpl
Piskorz, Witold - 131426
dc.contributor.authorpl
Sojka, Zbigniew - 131982
dc.date.accessioned
2015-12-02T13:48:14Z
dc.date.available
2015-12-02T13:48:14Z
dc.date.issuedpl
2015
dc.description.numberpl
33
dc.description.physicalpl
19180-19191
dc.description.volumepl
119
dc.identifier.doipl
10.1021/acs.jpcc.5b05136
dc.identifier.eissnpl
1932-7455
dc.identifier.issnpl
1932-7447
dc.identifier.uri
http://ruj.uj.edu.pl/xmlui/handle/item/17433
dc.languagepl
eng
dc.language.containerpl
eng
dc.rights.licence
bez licencji
dc.subtypepl
Article
dc.titlepl
Cobalt spinel at various redox conditions : DFT+U investigations into the structure and surface thermodynamics of the (100) facet
dc.title.journalpl
The Journal of Physical Chemistry. C
dc.typepl
JournalArticle
dspace.entity.type
Publication

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