Investigation of surface structures at catalytically important metals by UHV - electron spectroscopic and electrochemical methods

This thesis describes the work and results of an investigation of adsorbates at Pt(111) and Rh(100) single crystal electrodes and the basic electrochemical behavior of Rh(100) in perchlorate electrolyte. The measurements were made in a UHV (ultra high vacuum) - electrochemistry transfer system which allowed rapid contamination free UHV - electrolyte - UHV transfers. In UHV, low energy electron diffraction and Auger electron spectroscopic measurements were made and electrochemical characterization was made by linear sweep cyclic voltammetry. The target adsorbate systems were carbon monoxide and iodine. Electrosorption of carbon monoxide on Pt(111) produced a (\sqrt{3} \times 3)rect over-layer structure stable at room temperature which survived UHV transfer, careful LEED characterization and back immersion without changes in electrooxidation behavior. As a result of iodide exposure of submonolayers of CO created by electrooxidative stripping a second, lower cover c(\sqrt{3} \times 5)rect structure was found. The electrochemical behavior of Rh(100) in 0.1 M perchloric acid was also established. An asymmetric hydrogen region was found and a reversible surface reaction at the positive side of the double layer region was obtained. The general voltammetric evolution during multiple cycling was explained by perchlorate reduction and adsorption-desorption of the chlorides produced in the process. The reduction of perchlorates occurs when entering and leaving the hydrogen adsorption-desorption region. Electrooxidation of chemisorbed carbon monoxide indicated a coverage of one CO molecule per surface atom. After emersion of saturation CO coverages a (\sqrt{2} \times 4$\sqrt{2}$)R45$\sp\circ$ adlayer was detected. Back immersion of this structure gave a electrochemical coverage estimation in correspondence with the LEED data. In contrast to Pt(111), CO is spontaneously removed from the Rh(100) surface if immersed at open circuit. Immersion at a potential at the hydrogen evolution edge preserved the CO. The amount of CO lost due to UHV exposure corresponds approximately to the difference between unit coverage and the gas phase saturation coverage. Both gas phase and electolytic iodine produced a c(2 $\times$ 2) saturation coverage. Silver underpotential deposition onto this adlayer is distinct and qualitatively similar to the same behavior on iodine covered Rh(111). Chloride interference from reduced perchlorate was noticeable for both iodine and CO adlayers.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Chemistry

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2011

Author dc:creator

• Wasberg, Mikael Paul

Contributors dc:contributor

• Wieckowski, Andrzej

• Chemistry, Analytical

Statement dc:rights

• Copyright 1990 Wasberg, Mikael Paul

Language dc:language

eng

Identifier

AAI9114452
(UMI)AAI9114452

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/19932