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Oxygen reduction reaction at LaxCa1-xMnO3 nanostructures: interplay between A-site segregation and B-site valency

Oxygen reduction reaction at LaxCa1-xMnO3 nanostructures: interplay between A-site segregation and B-site valency
Oxygen reduction reaction at LaxCa1-xMnO3 nanostructures: interplay between A-site segregation and B-site valency
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 nano-particles were synthesised by an ionic liquid-based route, yielding phase-pure nanoparticles, across the entire range of compositions, with sizes between 20 and 35 nm. The 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 a 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 experimental data provides a consistent picture in which increasing electron density at the Mn sites 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.
2044-4753
1-8
Celorrio, Veronica
5ebb7fb5-a74c-4872-9795-5830dc915d0b
Calvillo, Laura
05ff21ed-97ce-4ea4-9b73-f4c181be59b0
Dann, Ellie
23e0a05e-1994-4cef-9717-b45de8948919
Granozzi, Gaetano
e1561b71-a42d-4c72-9028-3fb07183fceb
Aguadero, Ainara
d0665a8f-70ce-4c7e-8c45-98fac118f69f
Kramer, Denis
1faae37a-fab7-4edd-99ee-ae4c30d3cde4
Russell, Andrea
b6b7c748-efc1-4d5d-8a7a-8e4b69396169
Fermin, David
ea462f22-36cb-494d-a7dc-64ba55ee9a7e
Celorrio, Veronica
5ebb7fb5-a74c-4872-9795-5830dc915d0b
Calvillo, Laura
05ff21ed-97ce-4ea4-9b73-f4c181be59b0
Dann, Ellie
23e0a05e-1994-4cef-9717-b45de8948919
Granozzi, Gaetano
e1561b71-a42d-4c72-9028-3fb07183fceb
Aguadero, Ainara
d0665a8f-70ce-4c7e-8c45-98fac118f69f
Kramer, Denis
1faae37a-fab7-4edd-99ee-ae4c30d3cde4
Russell, Andrea
b6b7c748-efc1-4d5d-8a7a-8e4b69396169
Fermin, David
ea462f22-36cb-494d-a7dc-64ba55ee9a7e

Celorrio, Veronica, Calvillo, Laura, Dann, Ellie, Granozzi, Gaetano, Aguadero, Ainara, Kramer, Denis, Russell, Andrea and Fermin, David (2016) Oxygen reduction reaction at LaxCa1-xMnO3 nanostructures: interplay between A-site segregation and B-site valency. Catalysis Science & Technology, 1-8. (doi:10.1039/c6cy01105e).

Record type: Article

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 nano-particles were synthesised by an ionic liquid-based route, yielding phase-pure nanoparticles, across the entire range of compositions, with sizes between 20 and 35 nm. The 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 a 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 experimental data provides a consistent picture in which increasing electron density at the Mn sites 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.

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More information

Accepted/In Press date: 13 July 2016
e-pub ahead of print date: 13 July 2016
Organisations: Engineering Mats & Surface Engineerg Gp, Electrochemistry

Identifiers

Local EPrints ID: 398653
URI: https://eprints.soton.ac.uk/id/eprint/398653
ISSN: 2044-4753
PURE UUID: 8efc1a8d-22dd-45f0-836e-df0781752acc
ORCID for Andrea Russell: ORCID iD orcid.org/0000-0002-8382-6443

Catalogue record

Date deposited: 29 Jul 2016 13:19
Last modified: 15 Jun 2018 00:34

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