Preparation characterisation and evaluation of core shell electrocatalysts for PEMFCs

For oxygen reduction catalysis it has been shown that thin layers of platinum (shell)<br/>over a non-Pt core enhance the activity. In addition surface science studies have found that<br/>overlayers of one metal on another strongly modifies the electrocatalytic properties of the<br/>surface metal. The aim of this project is to develop this concept by the preparation of<br/>practical fuel cell catalysts based on the core-shell model and gain a fundamental<br/>understanding of their properties and behaviour. A key aspect of the work is to establish<br/>the physical characteristics required for a catalyst to show long-term stability as well as<br/>improved activity.<br/><br/>Chapter 1 introduces the PEM fuel cells, ORR electrocatalysts and the preparation and<br/>characterisation of core-shell type electrocatalysts. The experimental techniques,<br/>procedures and apparatus used for this work will be described in Chapter 2. The<br/>mechanism of the synthetic controlled-surface reaction (CSR) used to prepare the coreshell<br/>electrocatalysts was studied in Chapter 3. Then the focus will be on the palladiumcore<br/>and platinum-shell system in Chapter 4 and 5, where the effects of the Pt shell and the<br/>Pd core size on the electrocatalysts properties are investigated. The electrocatalysts<br/>prepared for these studies were assessed for their electrochemical stabilities and their ORR<br/>activities. Finally, Chapter 6 presents preliminary results on the iridium-core and platinumshell<br/>system.<br/><br/>The deposition of Pt on Pd and Ir cores using the CSR did not lead to a complete Pt<br/>coverage as Pt tended to deposit preferentially at the edges and corners on the core surface<br/>and then on Pt. Whereas an enhancement in the electrochemical stability of the Pt/Pd coreshell<br/>electrocatalysts was observed compared to a pure Pt electrocatalyst, the Pt/Ir coreshell<br/>showed poorer stability than Pt. Benefits in the ORR activity were gained with both<br/>the Pt/Pd and Pt/Ir core-shell electrocatalysts. This demonstrates that, due to the original<br/>properties of the core-shell-structured electrocatalysts, it is possible to use less Pt and still<br/>obtain an improvement in the ORR activity.

Name dc:type.qualificationname

Ph.D.

Level dc:type.qualificationlevel

doctoral

Grantor dc:publisher.institution

University of Southampton

Year dc:date.issued

2009

Author dc:creator

• Tessier, Beatrice Claire

Advisor dc:contributor.advisor

• Russell, A.E.