Characterisation of bimetallic alloy and core-shell electrocatalysts
Characterisation of bimetallic alloy and core-shell electrocatalysts
Core-shell electrocatalysts are of interest for the oxygen reduction reaction in proton exchange membrane fuel cells as enhancements in activity have been reported compared to the traditionally-used Pt/C electrocatalysts. To fully understand the origin of the activity of these samples, and how the structure changes in the electrochemical environment, full in situ structural characterisation is required. The aim of this work was to develop and apply in situ synchrotron based X-ray characterisation techniques (EXAFS, WAXS, SAXS and ASAXS) to study a set of well-defined Pd-core, Pt-shell electrocatalysts with 0.5, 1, 2 and 4 monolayers (ML) of Pt, with the primary motivation of determining the advantages and limitations of each technique when applied to materials of this nature.
Measurements were conducted in and ex situ to study the effect of Pt-shell thickness on the structure of the nanoparticles and the response to applied electrode potential. Catalyst electrodes subjected to accelerated ageing tests were also characterised to investigate the mechanisms of degradation responsible for an observed loss in electrochemical surface area, with the dominant mechanism found being dissolution for the core-shell catalysts with ? 2 ML shell and coalescence (Ostwald ripening) for the 4 ML.
EXAFS was found to be the most useful of the four techniques owing to the detailed structural information obtainable and the relative ease of data collection. The SAXS data provided information not obtained from the EXAFS, and combined with electrochemical measurements, enabled determination of the mechanisms of degradation. WAXS provided complementary information to the EXAFS. Attempts to fit the ASAXS data with a simplistic model were unsuccessful, thus, without the application of more complex theoretical models, little additional information could be obtained from this technique.
Wise, Anna MacDonald
22442664-6e56-4888-9f24-21317f6235e9
May 2012
Wise, Anna MacDonald
22442664-6e56-4888-9f24-21317f6235e9
Russell, Andrea E.
b6b7c748-efc1-4d5d-8a7a-8e4b69396169
Wise, Anna MacDonald
(2012)
Characterisation of bimetallic alloy and core-shell electrocatalysts.
University of Southampton, School of Chemistry, Doctoral Thesis, 172pp.
Record type:
Thesis
(Doctoral)
Abstract
Core-shell electrocatalysts are of interest for the oxygen reduction reaction in proton exchange membrane fuel cells as enhancements in activity have been reported compared to the traditionally-used Pt/C electrocatalysts. To fully understand the origin of the activity of these samples, and how the structure changes in the electrochemical environment, full in situ structural characterisation is required. The aim of this work was to develop and apply in situ synchrotron based X-ray characterisation techniques (EXAFS, WAXS, SAXS and ASAXS) to study a set of well-defined Pd-core, Pt-shell electrocatalysts with 0.5, 1, 2 and 4 monolayers (ML) of Pt, with the primary motivation of determining the advantages and limitations of each technique when applied to materials of this nature.
Measurements were conducted in and ex situ to study the effect of Pt-shell thickness on the structure of the nanoparticles and the response to applied electrode potential. Catalyst electrodes subjected to accelerated ageing tests were also characterised to investigate the mechanisms of degradation responsible for an observed loss in electrochemical surface area, with the dominant mechanism found being dissolution for the core-shell catalysts with ? 2 ML shell and coalescence (Ostwald ripening) for the 4 ML.
EXAFS was found to be the most useful of the four techniques owing to the detailed structural information obtainable and the relative ease of data collection. The SAXS data provided information not obtained from the EXAFS, and combined with electrochemical measurements, enabled determination of the mechanisms of degradation. WAXS provided complementary information to the EXAFS. Attempts to fit the ASAXS data with a simplistic model were unsuccessful, thus, without the application of more complex theoretical models, little additional information could be obtained from this technique.
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AWise_Thesis_Final.pdf
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Published date: May 2012
Organisations:
University of Southampton, Nanoelectronics and Nanotechnology
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Local EPrints ID: 341819
URI: http://eprints.soton.ac.uk/id/eprint/341819
PURE UUID: a494e36c-fa89-4146-9806-5d3102b3fcb6
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Date deposited: 12 Nov 2012 14:54
Last modified: 15 Mar 2024 05:01
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Author:
Anna MacDonald Wise
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