Preparation, characterisation and evaluation of core-shell electrocatalyst for PEMFCs

• Main Author: Tessier, Béatrice Claire
• Other Authors: Russell, Andrea
• Published: University of Southampton 2009
• Subjects: 541.39; QD Chemistry
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.523558

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