Electrochemical behaviour of pseudomorphic Ag and Cu monolayers on well-ordered single crystal surfaces and of Ir(210) nanofacets

Abstract

The topics of this thesis are multipurpose. The various systems all represent model surfaces for studies in electrocatalysis. Pseudomorphic Cu and Ag monolayers on various (111) surfaces of fcc crystals and Ir single crystal surfaces including nanofaceted Ir(210) have been prepared and electrochemically characterized. Cyclic voltammetry was used to characterize the electrochemical behaviour of pseudomorphic Cu and Ag monolayers and the Ir single crystal electrodes. In addition, the nanofaceted Ir(210) was characterized by in situ STM. In Chapter 4 the formation of a pseudomorphic Cu monolayer on Pd single crystals is reported. Two stages for Cu UPD from sulphate solution on Pd(111) and Pd(100) have been found. The properties of pseudomorphic Ag monolayers on Au(111), Pt(111), Pd(111), Rh(111) and Ir(111) have been studied (Chapter 5). There is a significant shift of the PZC for Ag monolayers on these substrates to more positive or negative values within a range of 0.32 V in comparison to massive Ag(111). This behaviour demonstrates the significant influence of the underlying substrate on the electronic properties of the Ag adlayer. Some Ag monolayers act as good electrocatalyst for glucose oxidation. In Chapter 6 the electrochemical behaviour of Ir(111) and Ir(210) electrodes is reported. A small reversible voltammetric peak was observed for Ir(111) in perchloric acid solution for the first time. This peak shifts by about 110 ± 10 mV per pH unit. It is noted that the oxygen reduction reaction commences just at the potential of this peak. The use of in situ STM for the study of a nanofaceted Ir(210) surface reveals the presence of nano-pyramids showing two (311) and one (110) facets. Nano-pyramids are shown to be stable in the presence of specifically adsorbed anions like sulphate. The faceted surface provides an ideal model system to study structure sensitivity in electrocatalytic reactions.