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The stability of LaMnO3 surfaces: A hybrid exchange density functional theory study of an alkaline fuel cell catalyst

The stability of LaMnO3 surfaces: A hybrid exchange density functional theory study of an alkaline fuel cell catalyst
The stability of LaMnO3 surfaces: A hybrid exchange density functional theory study of an alkaline fuel cell catalyst
LaMnO3 is an inexpensive alternative to precious metals (e.g. platinum) as a catalyst for the oxygen reduction reaction in alkaline fuel cells. In fact, recent studies have shown that among a range of non-noble metal catalysts, LaMnO3 provides the highest catalytic activity. Despite this, very little is known about LaMnO3 in the alkaline fuel cells environment, where the orthorhombic structure is most stable. In order to understand the reactivity of orthorhombic LaMnO3 we must first understand the surface structure. Hence, we have carried out calculations on its electrostatically stable low index surfaces using hybrid-exchange density functional theory, as implemented in CRYSTAL09. For each surface studied the calculated structure and formation energy is discussed. Among the surfaces studied the (100) surface was found to be the most stable with a formation energy of 0.98 J/m2. The surface energies are rationalised in terms of the cleavage of Jahn-Teller distorted Mn-O bonds, the compensation of undercoordination for ions in the terminating layer and relaxation effects. Finally, the equilibrium morphology of orthorhombic LaMnO3 crystals is predicted, allowing us to speculate about likely surface reaction sites.
2050-7488
11152-11162
Ahmed, E.A.
289f8f1d-fe9b-4eb4-a1d0-efc70e075d03
Mallia, G.
fe9957f3-28c0-4a86-9153-03b369b25afd
Kramer, D.
1faae37a-fab7-4edd-99ee-ae4c30d3cde4
Kucernak, A.R.
ccd04048-9fc0-4ded-a121-3dbd9a34480a
Harrison, N.M.
e40abf85-bc7e-4153-8f21-79e086c28ac3
Ahmed, E.A.
289f8f1d-fe9b-4eb4-a1d0-efc70e075d03
Mallia, G.
fe9957f3-28c0-4a86-9153-03b369b25afd
Kramer, D.
1faae37a-fab7-4edd-99ee-ae4c30d3cde4
Kucernak, A.R.
ccd04048-9fc0-4ded-a121-3dbd9a34480a
Harrison, N.M.
e40abf85-bc7e-4153-8f21-79e086c28ac3

Ahmed, E.A., Mallia, G., Kramer, D., Kucernak, A.R. and Harrison, N.M. (2013) The stability of LaMnO3 surfaces: A hybrid exchange density functional theory study of an alkaline fuel cell catalyst. Journal of Materials Chemistry A, 1 (37), 11152-11162. (doi:10.1039/C3TA11382E).

Record type: Article

Abstract

LaMnO3 is an inexpensive alternative to precious metals (e.g. platinum) as a catalyst for the oxygen reduction reaction in alkaline fuel cells. In fact, recent studies have shown that among a range of non-noble metal catalysts, LaMnO3 provides the highest catalytic activity. Despite this, very little is known about LaMnO3 in the alkaline fuel cells environment, where the orthorhombic structure is most stable. In order to understand the reactivity of orthorhombic LaMnO3 we must first understand the surface structure. Hence, we have carried out calculations on its electrostatically stable low index surfaces using hybrid-exchange density functional theory, as implemented in CRYSTAL09. For each surface studied the calculated structure and formation energy is discussed. Among the surfaces studied the (100) surface was found to be the most stable with a formation energy of 0.98 J/m2. The surface energies are rationalised in terms of the cleavage of Jahn-Teller distorted Mn-O bonds, the compensation of undercoordination for ions in the terminating layer and relaxation effects. Finally, the equilibrium morphology of orthorhombic LaMnO3 crystals is predicted, allowing us to speculate about likely surface reaction sites.

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e-pub ahead of print date: 7 August 2013
Organisations: Engineering Mats & Surface Engineerg Gp

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Local EPrints ID: 355553
URI: https://eprints.soton.ac.uk/id/eprint/355553
ISSN: 2050-7488
PURE UUID: 2005a298-3a87-44a4-830a-61ad42fc0056

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Date deposited: 02 Sep 2013 13:57
Last modified: 18 Jul 2017 03:46

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Contributors

Author: E.A. Ahmed
Author: G. Mallia
Author: D. Kramer
Author: A.R. Kucernak
Author: N.M. Harrison

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