Oxygen Reduction Reaction at LaxCa1-xMnO3 Nanostructures: Interplay between A-site Segregation and B-site Valency

David J Fermin, Veronica Celorrio, Laura Calvillo, Ellie Dann, Gaetano Granozzi, Ainara Aguadero, Andrea Russell, Denis Kramer

Research output: Contribution to journalArticle (Academic Journal)peer-review

43 Citations (Scopus)
508 Downloads (Pure)

Abstract

The mean activity of surface Mn sites at LaxCa1-xMnO3 nanostructures towards the oxygen reduction reaction (ORR) in alkaline solution is assessed as a function of the oxide composition. Highly active oxide nanoparticles were synthesised by an ionic liquid based route, yielding phase-pure nanoparticles, across the entire range of composition, with sizes between 20 and 35 nm. Bulk vs. surface composition and structure are investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and X-ray absorption near edge spectroscopy (XANES). These techniques allow quantification of not only changes in the mean oxidation state of Mn as function of x, but also the extent of A-site surface segregation. Both trends manifest themselves in the electrochemical responses associated with surface Mn sites in 0.1 M KOH solution. The characteristic redox signatures of Mn sites are used to estimate their effective surface number density. This parameter allows comparing, for the first time, the mean electrocatalytic activity of surface Mn sites as a function of the LaxCa1-xMnO3 composition. The ensemble of the experimental data provides a consistent picture in which increasing electron density at the Mn site leads to an increase in the ORR activity. We also demonstrate that normalisation of electrochemical activity by mass or specific surface area may result in inaccurate structure-activity correlations.
Original languageEnglish
Pages (from-to)7231-7238
Number of pages6
JournalCatalysis Science and Technology
Volume6
Issue number19
Early online date13 Jul 2016
DOIs
Publication statusPublished - 7 Oct 2016

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