Enhancing the oxygen vacancy formation and migration in bulk chromium(iii) oxide by alkali metal doping: a change from isotropic to anisotropic oxygen diffusion

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dc.check.date2018-07-11
dc.check.infoAccess to this article is restricted for 12 months after publication by request of the publisher.en
dc.contributor.authorCarey, John J.
dc.contributor.authorNolan, Michael
dc.contributor.funderEuropean Commissionen
dc.contributor.funderSeventh Framework Programmeen
dc.contributor.funderScience Foundation Irelanden
dc.contributor.funderHigher Education Authorityen
dc.contributor.funderEuropean Cooperation in Science and Technologyen
dc.date.accessioned2017-11-02T12:29:50Z
dc.date.available2017-11-02T12:29:50Z
dc.date.issued2017-07-11
dc.date.updated2017-11-02T12:19:09Z
dc.description.abstractOxygen vacancy formation and migration are vital properties for reducible oxides such as TiO2, CeO2 and Cr2O3 as the oxygen storage capacity (OSC) of these materials are important for a wide range of applications in photovoltaics, oxidative catalysis and solid oxide fuel cells. Substitutional doping these transition metal oxides enhances their OSC potential, in particular for oxygenation and surface reaction chemistry. This study uses density functional theory with on-site Coulomb interactions (PBE+U) for Cr 3d states (+U = 5 eV) and O 2p states (+U = 5.5 eV) to calculate the oxygen vacancy formation energy and oxygen diffusion pathways for alkali metal (Li, K, Na, Rb) doping of bulk chromium(III) oxide (α-Cr2O3). Substitutional doping of the lattice Cr3+ cations with alkali metals that have a +1 oxidation state, creates two hole states on the neighbouring lattice O atoms, and removal of a lattice oxygen charge compensates the dopants by filling the holes. The removal of the next oxygen describes the reducibility of doped Cr2O3. The oxygen vacancy formation energy is greatly promoted by the alkali dopants with a correlation between the ionic radius of the dopant cation and vacancy formation energy; larger dopants (K, Rb) improve the reducibility more than the smaller dopants (Li, Na). The activation barriers for oxygen migration along different directions in the alkali metal doped Cr2O3 bulk were also calculated to examine the effect of doping on the oxygen migration. The calculated activation energies for the undoped chromia are symmetric in three dimensions (isotropic) and the presence of the dopants break this isotropy. Alkali dopants promote oxygen migration in the oxygen intra-layers while suppressing oxygen migration across the Cr cation layers. The smaller dopants (Li, Na) facilitate easier migration in the oxygen intra-layers to a greater extent than the larger dopants (K, Rb). The Na–Cr2O3 bulk promotes both oxygen vacancy formation and migration which makes it a novel candidate for anode materials in medium temperature SOFCs and battery applications.en
dc.description.sponsorshipScience Foundation Ireland and Higher Education Authority (SFI/HEA funded Irish Centre for High-end Computing (ICHEC) and SFI funded local clusters at Tyndall); European Commission (European Cooperation in Science and Technology COST Action CM1104 “Reducible Metal Oxides, Structure and Function”)en
dc.description.statusPeer revieweden
dc.description.versionAccepted Versionen
dc.format.mimetypeapplication/pdfen
dc.identifier.citationCarey, J. J. and Nolan, M. (2017) 'Enhancing the oxygen vacancy formation and migration in bulk chromium(iii) oxide by alkali metal doping: a change from isotropic to anisotropic oxygen diffusion', Journal of Materials Chemistry A, 5(30), pp. 15613-15630. doi: 10.1039/C7TA00315Cen
dc.identifier.doi10.1039/C7TA00315C
dc.identifier.endpage15630en
dc.identifier.issn2050-7488
dc.identifier.issued30en
dc.identifier.journaltitleJournal of Materials Chemistry Aen
dc.identifier.startpage15613en
dc.identifier.urihttps://hdl.handle.net/10468/4948
dc.identifier.volume5en
dc.language.isoenen
dc.publisherRoyal Society of Chemistryen
dc.relation.projectinfo:eu-repo/grantAgreement/EC/FP7::SP1::NMP/604296/EU/Catalytic Partial Oxidation of Bio Gas and Reforming of Pyrolysis Oil (Bio Oil) for an Autothermal Synthesis Gas Production and Conversion into Fuels/BIOGO-FOR-PRODUCTIONen
dc.rights© The Royal Society of Chemistry 2017. This is the Accepted Manuscript version of a published work that appeared in final form in Journal of Materials Chemistry A. To access the final published version of record, see http://pubs.rsc.org/en/content/articlepdf/2017/ta/c7ta00315cen
dc.subjectActivation energyen
dc.subjectAnodesen
dc.subjectChemical activationen
dc.subjectChromiumDensity functional theoryen
dc.subjectDiffusion in gasesen
dc.subjectDoping (additives)en
dc.subjectFuel cellsen
dc.subjectFuel storageen
dc.subjectLithiumen
dc.subjectMetalsen
dc.subjectOxygenen
dc.subjectPositive ionsen
dc.subjectSolid oxide fuel cells (SOFC)en
dc.subjectSurface reactionsen
dc.subjectTransition metal compoundsen
dc.subjectTransition metalsen
dc.subjectOxygen vacanciesen
dc.subjectActivation barriersen
dc.subjectAlkali metal dopingen
dc.subjectBattery applicationsen
dc.subjectOxygen storage capacityen
dc.subjectOxygen vacancy formation energiesen
dc.subjectReaction chemistryen
dc.subjectTransition-metal oxidesen
dc.subjectVacancy formation energiesen
dc.titleEnhancing the oxygen vacancy formation and migration in bulk chromium(iii) oxide by alkali metal doping: a change from isotropic to anisotropic oxygen diffusionen
dc.typeArticle (peer-reviewed)en
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