Electrochemical studies of the oxygen reduction reaction: platinum and platinum bimetallic single crystal electrodes

Doctoral thesis English OPEN
Brew, Ashley
  • Subject: QD

The general objective of this investigation was to elucidate the effect that surface species such as OHads, Oads and the interfacial water layer have on the oxygen reduction reaction activity of active platinum and platinum alloy catalysts in perchloric acid electrolyte. To that end, these are the investigations that were carried out:\ud [Pt n{111}x{100}] and [Pt n{100}x111}] series of surfaces. These surfaces exhibit OHads/Oads formation at terrace and step sites in the potential range relevant to loss in ORR activity. The increase in activity observed at low step density was assigned to the disruption by steps of a long range ordered OHads terrace over-layer.\ud Hydrogen peroxide oxidation/reduction reaction activity of [Pt n{111}x{100}] and [Pt n{100}x{111}] series of surfaces. The results imply that if oxygen reduction proceeds via the series pathway the rate determining step lies in the later stages of the reaction, i.e after H2O2 formation.\ud CV and ORR of kinked surfaces based upon Pt{332}. These results indicate that low-coordinate {100} kink sites do not have unique ORR activity, i.e. their activity is identical to {100} linear step sites.\ud CV, XPS, STM and ORR of single crystal Pt{111}-M (where M=Ni, Co or Fe) alloy surfaces showed that the onset of electrochemical oxide formation shifts positive in the order Ni, Co, Fe. This shift correlated with increased activity towards the ORR which we ascribe to the greater availability of highly active metallic sites for oxygen reduction at ORR potentials.\ud (1x1) and disordered (1x2) surface atomic arrangements of Pt{110} were created and compared. For the first time, the voltammetry of the Pt{110}-(1x1) surface has been reported in aqueous perchloric acid and sodium hydroxide. The activity of the Pt{110}-(1x1) surface for oxygen reduction was found to be approximately 30 - 40 mV less active than the disordered (1x2) surface.
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    89 references, page 1 of 9

    1.1.2 An Overview of Proton Exchange Membrane Fuel Cells (PEMFCs)

    1.2 Background and History of Catalysis, Electrochemistry and Electro-catalysis

    1.2.1 Electrode Kinetics and the Butler-Volmer Equation

    1.2.2 Adsorption

    1.2.3 The Electrical Double Layer

    1.3 The Surface Atomic Structure of Metals

    1.3.1 The Miller Index and Microfacet Notation Systems

    1.4 Electrochemical Techniques

    1.4.1 Mass Transport in Electrochemistry

    1.4.1.1 Diffusion in Chronoamperometry

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