Heterogeneous catalysis is essential to many industrial applications. These catalysts are often comprised of supported nanoparticles, which contain various different surface sites. For some... Show moreHeterogeneous catalysis is essential to many industrial applications. These catalysts are often comprised of supported nanoparticles, which contain various different surface sites. For some reactions, the presence of specific surface sights dominates the overall reactivity. Fundamental insight into the influence of different surface sites on the surface reaction dynamics may lead to better catalyst design in the future. In this thesis, we combine ultra-high vacuum techniques and (curved) single crystal surfaces to study surface structure effects relevant to heterogeneous catalysis. We study how step edges on a platinum surface affect (elementary) reactions that occur in oxygen reduction: hydrogen dissociation, hydrogen recombination, and oxygen reduction. Show less
Heterogeneous catalysis is very important for industrial applications and the environment. It is known that precious metals, such as Pd and Pt, can be good catalyst materials for various reactions.... Show moreHeterogeneous catalysis is very important for industrial applications and the environment. It is known that precious metals, such as Pd and Pt, can be good catalyst materials for various reactions. However, these metals are expensive and their catalytic action is not yet completely understood. In the search for better and cheaper materials, more fundamental knowledge is necessary. We use ultra-high vacuum techniques and well-ordered Pd and Pt single crystals to further investigate the oxygen dissociation process and the interaction of water with deuterated surfaces. Show less
We have investigated the dissociation state of water on platinum electrodes. The desorption of D2, O2, and H2O is influenced significantly by the presence of step sites and the geometry of those... Show moreWe have investigated the dissociation state of water on platinum electrodes. The desorption of D2, O2, and H2O is influenced significantly by the presence of step sites and the geometry of those sites. Under UHV conditions OH groups can be formed on Pt(111) by pre-covering the surface with O adatoms, causing water to dissociate. We have shown that on stepped platinum surfaces OHad might not be as readily formed as one would assume based on the energetics of OH adsorption alone. Even though the Pt(533) and Pt(553) surfaces have similar geometries, the hydrophobicity on the deuterated surface is surprisingly different: on D/Pt(533) the surface is hydrophobic with water clustering at steps, whereas the entire surface is wet on D/Pt(553). Under electrochemical conditions we show that in spite of the similar looking cyclic voltammograms, the kinetics of underpotential deposited hydrogen are significantly different in acidic and alkaline media. In alkaline media the ad- and desorption process is slow, whereas it is very fast in acidic media. We have pointed out three discrepancies in the current interpretation of the blank cyclic voltammetry of stepped platinum surfaces and propose a co-adsorption model that accounts for these discrepancies. Show less
