Abstract: Fundamental surface science investigations are primarily concerned with understanding the chemistry that occurs at the interface of phases, such as the solid/gas, solid/liquid, and liquid/vapor interface. Surface science investigations have led to breakthroughs in understanding chemisorption and physisorption on heterogeneous catalysts, reactions that occur at the interface of electrodes, and hydrogen bonding in aqueous solutions. Fundamental understanding of the chemistry that occurs on surfaces can lead to better material design, such as more efficient catalysts, and insight into complex chemical processes that are not well understood, such as how a solvent affects the electronic properties of solutes.
The work presented in this thesis includes fundamental studies on both solid/gas and liquid/vapor interfaces. Chapter 1 discusses the synthesis and characterization of a Cu/TiO2 nanoparticle model catalyst system supported on a highly oriented pyrolytic graphite (HOPG) substrate. Supporting the nanoparticles on an inert HOPG substrate allows for the rigorous characterization of this model catalyst using advanced surface science techniques. Further reactivity and stability studies were then conducted on this system.
Chapter 2 investigates the thermal reduction of CO2 over the Cu/TiO2/HOPG model catalyst through the use of ambient pressure X‑ray photoelectron spectroscopy (AP‑XPS) at a synchrotron light source. The Cu/TiO2/HOPG sample was heated in an atmosphere of CO2 and H2 reactant gases and AP‑XPS measurements were taken in an effort to observe formation of intermediates on the catalyst surface. Using the synchrotron, we are able to obtain information at the near surface and bulk of the catalyst in order to elucidate fundamental information on the CO2 hydrogenation reaction mechanism.
The electrochemical reactivity and stability of the Cu/TiO2/HOPG catalyst is discussed in Chapter 3. Differential electrochemical mass spectrometry (DEMS) measurements showed that this catalyst forms methane as its major product under electrochemical CO2 reduction conditions. The stability of the Cu and TiO2 nanoparticles were investigated using cyclic voltammetry and chronoamperometry.
In an effort to fundamentally study the Cu/ZnO system, similar to the Cu/TiO2 system, the synthesis of ZnO nanoparticles on HOPG was attempted using PVD. The synthesis of these nanoparticles is discussed in Chapter 4, which details the various parameters that were adjusted in order to optimize the PVD process. Photodeposition and stability studies of the synthesized ZnO/HOPG samples were also investigated.
The study of liquid interfaces using liquid‑jet ambient‑pressure X‑ray photoelectron spectroscopy (LJ‑APXPS) is discussed in Chapter 5. Various solutes in aqueous solutions were investigated using synchrotron radiation in order to study the solvation induced changes in the electronic structure of solutes from the surface to the bulk of the solution and as a function of pH. These investigations provide insight into the solvent effects for molecular solutes that reside at or near the liquid/vapor interface in solution.