Template-assisted Electrodeposition and Model Electrodes Studied by Electron Microscopy and High Energy X-ray Diffraction

Abstract: There is a great interest in studying detailed changes at electrode surfaces during electrochemical processes to better understand the electrochemical reactions at the electrode surface-liquid interface and improve the electrode efficiency. The Au(110) surface has a known (1$\times$2) missing row reconstruction in vacuum conditions, which can change into higher-order (1$\times$3), (1$\times$5), and (1$\times$7) depending on environment. Although less studied than under vacuum conditions, surface studies have been performed during electrochemical reactions where similar reconstructions have been noted. In this thesis high energy surface x-ray diffraction measurements from a Au(110) surface in HClO$_4$ and H$_2$SO$_4$ have been performed at varying potentials both \textit{in situ} and \textit{ex situ}. The results confirm previously shown electrode potential-dependence of the reconstruction in HClO$_4$. A (1$\times$3) missing row reconstruction is present at negative potentials, which transitions into a (1$\times$2) reconstruction before the recondition is effectively lifted at higher positive potentials. The transitions are shown to still contain (1$\times$3) reconstruction up until a clear (1$\times$2) reconstruction is present, which can indicate domains of (1$\times$3) and (1$\times$2) reconstruction coexisting. For Au(110) in H$_2$SO$_4$, there is a similar transition behavior from a (1$\times$3) reconstruction. The transition seems to occur at higher potentials than for HClO$_4$, but a clear (1$\times$2) reconstruction is never present. A second project focused on the synthesis process of nanoporous templates and electrodeposition of Sn and Pt. A two-step anodization process was used to create porous alumina templates with well-ordered pores. Electrodeposition is a method by which the nanowires can be built atom by atom in the pores without limitations of sample size. The deposition and wire properties have been studied before. However, there is an interest in developing the deposition process and studying the efficiency to enable the fabrication of bi-metallic SnPt nanowires. Sn electrodeposition was performed with a Sine potential, a symmetrical pulse shape, and an asymmetrical pulse shape. While the pulsed deposition resulted in materials in the pores, the efficiency was low, and the pores were not filled even after long deposition times. The asymmetrical pulse shape enabled higher pore filling. The Pt deposition with the same methods was unsuccessful due to high solution acidity. Nonetheless, the new pulse shape opens up for further development of the deposition process.