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Relationship between Mn oxidation state changes and oxygen reduction activity in (La,Ca)MnO3 as probed by in situ XAS and XES

Relationship between Mn oxidation state changes and oxygen reduction activity in (La,Ca)MnO3 as probed by in situ XAS and XES
Relationship between Mn oxidation state changes and oxygen reduction activity in (La,Ca)MnO3 as probed by in situ XAS and XES
In situ X-ray absorption and emission spectroscopies (XAS and XES) are used to provide details regarding the role of the accessibility and extent of redox activity of the Mn ions in determining the oxygen reduction activity of LaMnO3 and CaMnO3, with the XANES providing the average oxidation state, the EXAFS the local coordination environment, and the XES the population ratios of the Mn2+, Mn3+, and Mn4+ sites as a function of the applied potential. For LaMnO3 the XANES and XES show that Mn3+ is formed, but Mn4+ ions are retained, which leads to the 4e- reduction between 0.85 and 0.6 V. At more negative potentials, down to 0.2 V, EXAFS confirms an increase in oxygen vacancies as evidenced by changes in the Mn-O coordination distance and number, whilst the XES shows that the Mn3+ to Mn4+ ratio increases. For CaMnO3 the XANES and XES show formation of both Mn3+ and Mn2+ as the potential is made more negative, with little retention of Mn4+ at 0.2 V. The EXAFS for CaMnO3 also indicates the formation of oxygen vacancies, but in contrast to LaMnO3 this is accompanied by loss of the perovskite structure leading to structural collapse. The results presented have implications in terms of understanding of both the pseudocapacitive response of Mn oxide electrocatalysts and the processes behind degradation of the activity of the materials.
CaMnO3, LaMnO3, Manganese Redox, X-ray absorption/emission, oxygen reduction reaction, perovskite oxides
2155-5435
6431-6439
Celorrio, Veronica
5ebb7fb5-a74c-4872-9795-5830dc915d0b
Leach, Andrew Stephen
eb2fee87-ab58-4a28-9319-529de90d1708
Huang, Haoliang
132a8eda-b800-4fa7-9583-6b4306f30247
Hayama, Shusaku
dbaecfbe-b0a6-4b21-9030-b2942d42b33c
Freeman, Adam
f69d70ef-c582-43a4-aec6-1762a99821b9
Inwood, David W
5364f809-b866-45aa-8b43-3db6113fb0e6
Fermin, D.J.
3bfcec3e-75fc-487b-9367-ea8c805f4c0d
Russell, Andrea E.
b6b7c748-efc1-4d5d-8a7a-8e4b69396169
Celorrio, Veronica
5ebb7fb5-a74c-4872-9795-5830dc915d0b
Leach, Andrew Stephen
eb2fee87-ab58-4a28-9319-529de90d1708
Huang, Haoliang
132a8eda-b800-4fa7-9583-6b4306f30247
Hayama, Shusaku
dbaecfbe-b0a6-4b21-9030-b2942d42b33c
Freeman, Adam
f69d70ef-c582-43a4-aec6-1762a99821b9
Inwood, David W
5364f809-b866-45aa-8b43-3db6113fb0e6
Fermin, D.J.
3bfcec3e-75fc-487b-9367-ea8c805f4c0d
Russell, Andrea E.
b6b7c748-efc1-4d5d-8a7a-8e4b69396169

Celorrio, Veronica, Leach, Andrew Stephen, Huang, Haoliang, Hayama, Shusaku, Freeman, Adam, Inwood, David W, Fermin, D.J. and Russell, Andrea E. (2021) Relationship between Mn oxidation state changes and oxygen reduction activity in (La,Ca)MnO3 as probed by in situ XAS and XES. ACS Catalysis, 11, 6431-6439. (doi:10.1021/acscatal.1c00997). (In Press)

Record type: Article

Abstract

In situ X-ray absorption and emission spectroscopies (XAS and XES) are used to provide details regarding the role of the accessibility and extent of redox activity of the Mn ions in determining the oxygen reduction activity of LaMnO3 and CaMnO3, with the XANES providing the average oxidation state, the EXAFS the local coordination environment, and the XES the population ratios of the Mn2+, Mn3+, and Mn4+ sites as a function of the applied potential. For LaMnO3 the XANES and XES show that Mn3+ is formed, but Mn4+ ions are retained, which leads to the 4e- reduction between 0.85 and 0.6 V. At more negative potentials, down to 0.2 V, EXAFS confirms an increase in oxygen vacancies as evidenced by changes in the Mn-O coordination distance and number, whilst the XES shows that the Mn3+ to Mn4+ ratio increases. For CaMnO3 the XANES and XES show formation of both Mn3+ and Mn2+ as the potential is made more negative, with little retention of Mn4+ at 0.2 V. The EXAFS for CaMnO3 also indicates the formation of oxygen vacancies, but in contrast to LaMnO3 this is accompanied by loss of the perovskite structure leading to structural collapse. The results presented have implications in terms of understanding of both the pseudocapacitive response of Mn oxide electrocatalysts and the processes behind degradation of the activity of the materials.

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Accepted/In Press date: 5 May 2021
Keywords: CaMnO3, LaMnO3, Manganese Redox, X-ray absorption/emission, oxygen reduction reaction, perovskite oxides

Identifiers

Local EPrints ID: 449407
URI: http://eprints.soton.ac.uk/id/eprint/449407
ISSN: 2155-5435
PURE UUID: ac3ca563-153b-46b0-aaa9-b769ebfc11b2
ORCID for Andrea E. Russell: ORCID iD orcid.org/0000-0002-8382-6443

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Date deposited: 27 May 2021 16:31
Last modified: 28 Apr 2022 01:43

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Contributors

Author: Veronica Celorrio
Author: Andrew Stephen Leach
Author: Haoliang Huang
Author: Shusaku Hayama
Author: Adam Freeman
Author: David W Inwood
Author: D.J. Fermin

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