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

Abstract

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.

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Identifiers

ORCID for Andrea E. Russell: orcid.org/0000-0002-8382-6443

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