The stability of single crystal Pt and Pt3Ni surfaces during electro-oxidation



Darlington, Michael
The stability of single crystal Pt and Pt3Ni surfaces during electro-oxidation. PhD thesis, University of Liverpool.

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Abstract

In an e�ort to gain a fundamental understanding of the link between catalyst surface structure, reactivity and stability, experiments have been performed on Pt(111), Pt3Ni(111) and Pt(100) single crystal electrode surfaces via a combina- tion of in-situ structural probes and electrochemical (cyclic voltammetry) mea- surements. Pt(111), which is the least active of the low index surface for the Oxygen Reduction Reaction (ORR), showed morphological changes after oxida- tion reduction cycles, with the formation of stable platinum adislands. The more active Pt(100) surface undergoes a drastic roughening of the surface during ox- idation/reduction cycles, which is due to the fact that the surface is unlikely to recrystallise into the more open (100) surface structure. In essence, although the Pt surfaces with a more open atomic geometry, e.g. (100) and (110), are more reactive than the close-packed (111) surface, they are intrinsically less stable. The bimetallic alloy Pt3Ni(111) surface has been shown to be over 10 times more ac- tive for the ORR than pure Pt(111) and exhibits a compositional oscillation at the surface which is formed of Pure Pt. Upon repetitive cycling the Pt3Ni(111) surface undergoes a similar morphological change to that of Pt(111), where the formation of adislands was seen in STM measurements. These adislands retain some of the active segregated surface structure, preserving the electronic modi�cation due to the Ni-rich subsurface. This leads to a stable surface that remains more active than the pure Pt(111) electrode after prolonged cycling of the potential into the region of oxidation/reduction. Perhaps the key insight that can be obtained from these experiments is that electrode activity towards the ORR is intrinsically linked to surface stability, i.e. the more active the surface, the less stable it is. This, in fact, may be a general e�ect in electrocatalysis.

Item Type: Thesis (PhD)
Additional Information: Date: 2014-09 (completed)
Depositing User: Symplectic Admin
Date Deposited: 22 Jan 2015 08:31
Last Modified: 17 Dec 2022 01:27
DOI: 10.17638/02005579
URI: https://livrepository.liverpool.ac.uk/id/eprint/2005579