Restructuring of an Ir(210) electrode surface by potential cycling
Summary This study addresses the electrochemical surface faceting and restructuring of Ir(210) single crystal electrodes. Cyclic voltammetry measurements and in situ scanning tunnelling microscopy are used to probe structural changes and variations in the electrochemical behaviour after potential cycling of Ir(210) in 0.1 M H2SO4. Faceted structures are obtained electrochemically as a function of time by cycling at a scanrate of 1 V·s−1 between −0.28 and 0.70 V vs SCE, i.e., between the onset of hydrogen evolution and the surface oxidation regime. The electrochemical behaviour in sulfuric acid solution is compared with that of thermally faceted Ir(210), which shows a sharp characteristic voltammetric peak for (311) facets. Structures similar to thermally-induced faceted Ir(210) are obtained electrochemically, which typically correspond to polyoriented facets at nano-pyramids. These structures grow anisotropically in a preferred direction and reach a height of about 5 nm after 4 h of cycling. The structural changes are reflected in variations of the electrocatalytic activity towards carbon monoxide adlayer oxidation.
Kinetics of hydrogen underpotential deposition at iridium in sulfuric and perchloric acids
Abstract Kinetics of hydrogen underpotential deposition (H UPD) reaction was studied at a polycrystalline iridium electrode in sulfuric acid and perchloric acid using cyclic voltammetry and electrochemical impedance spectroscopy. Cyclic voltammograms in both acids displayed peaks due to adsorption and desorption of hydrogen. The hydrogen adsorption properties of Ir are similar to those of Pt and Rh. Differences in cyclic voltammograms of Ir in H 2 SO 4 and HClO 4 were due to ionic adsorption. The kinetics of H UPD at Ir was determined using electrochemical impedance spectroscopy. Double layer and adsorption capacitances and charge transfer resistances of the H UPD were determined as functions of electrode potential. It was found that the kinetics of the H UPD reaction at Ir was slower than that at polycrystalline Pt but faster than that at polycrystalline Rh, Ru and Pd. These results give a new insight into electrosorption properties of the iridium catalyst in acidic solutions.
SR topography of plastically deformed Fe-Si bicrystals - observation in situ and post mortem
SR reflection topography was applied to study the interaction of slip dislocations with the grain boundaries in Fe-4at%Si bicrystals deformed by compression. Three experimental settings with either a white or monochromatic beam were used and the corresponding orientation contrast analysed. Dislocation transmission through the grain boundary was observed in bicrystals with favourable geometry of the slip systems.