In most applications, electrocatalysts exhibit a large surface area to volume ratio, for example using nanoparticles. To fully understand fundamental electrochemical processes at the length scale... Show moreIn most applications, electrocatalysts exhibit a large surface area to volume ratio, for example using nanoparticles. To fully understand fundamental electrochemical processes at the length scale of these nanoparticles, it is necessary to use specialized experimental techniques. In this thesis, the stability and activity of platinum electrode surfaces are studied at the nano- and micrometer scale using Electrochemical Scanning Probe Microscopy (EC-SPM) techniques. Chapters 2 and 3 describe the roughening of an atomically flat Pt(111) surface upon repetitive oxidation and reduction. These data were acquired using a combination of Electrochemical Scanning Tunneling Microscopy (EC-STM) and Cyclic Voltammetry (CV). Chapter 4 describes the development of a new technique to resolve small differences in local reactivity: voltammetric Scanning Electrochemical Cell Microscopy (SECCM). The power of this technique is demonstrated by studying the reactivity of a polycrystalline Pt sample towards hydrazine oxidation. Finally, Chapter 5 compares the reactivity of small Pt ultramicroelectrodes to that of conventional macroelectrodes. Show less
Catalysis is one of the most important technical and scientific developments, on which present-day society is based. For example, it is crucial to the production of fertilizers or clean... Show more Catalysis is one of the most important technical and scientific developments, on which present-day society is based. For example, it is crucial to the production of fertilizers or clean fuels and needed for the abatement of exhaust gases. Frequently, the employed catalysts are being discovered in a very empirical way; by trial and error. However, designing catalysts based on detailed understanding is preferred. Obtaining understanding is very difficult, because catalysts are very complex materials. Furthermore, its properties often depend on the atmosphere surrounding the catalysts, i.e., the temperature and pressure of reactants and products, which they are exposed to, and these properties also change over time. The major part of this thesis focuses on structural changes of Pt model catalysts exposed to high oxygen pressures at elevated temperatures. The changes were measured with a ReactorSTM, a special version of a scanning tunneling microscope (STM) adapted to operate at high pressure and temperatures. These observations show that various surface oxide with a single-layer thickness form under reaction conditions. These oxides are structurally and chemically different from the Pt bulk oxides. The second part describes a set of experiments to understand the role of low-coordinated atoms and water in Au-catalyzed CO oxidation. Show less
This thesis describes the construction of a second generation high-pressure, high-temperature scanning tunneling microscope, the ReactorSTM, with which the surfaces of catalysts can be studied... Show moreThis thesis describes the construction of a second generation high-pressure, high-temperature scanning tunneling microscope, the ReactorSTM, with which the surfaces of catalysts can be studied under relevant reaction conditions. Furthermore, the thesis describes three separate catalytic systems at ~ 1 bar, and elevated temperatures. Firstly, NO reduction on Pt(100), in which a mathematical model for the reaction mechanism, following Langmuir-Hinshelwood kinetics, is proposed. Secondly, CO oxidation, in which the Pt(110) surface is atomically resolved at high p, T. Thirdly, the thesis describes a successful pilot experiment about the hydrodesulphurization of thiophene, which is catalytically activated by molybdenum disulphide nano-crystallites on an Au(111) support. Show less
