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.
Electrochemical behaviour of nano-faceted Ir(2 1 0)
Nano-faceted Ir(2 1 0) surfaces have been obtained by inductive heating and cooling in an oxygen-containing gas atmosphere. The behaviour of the nanostructured Ir(2 1 0) electrode in contact with 0.1 M H2SO4 has been studied by cyclic voltammetry and in-situ scanning tunnelling microscopy (STM). The nano-facets are found to be stable under electrochemical conditions, which is in agreement with theoretical predictions [P. Kaghazchi, W. Chen, H. Wang, I. Ermanoski, T.E. Madey, T. Jacob, ACS Nano 2 (2008) 1280]. A characteristic needle peak at −0.18 V in cyclic voltammograms for Ir(2 1 0) electrodes in sulphuric acid solution indicates the presence and quality of the faceted nanostructure. In-situ STM images show a homogenous distribution of small three-sided pyramids with an average size of ca. 30 nm. The nano-pyramids consist of facets with (3 1 1), (3 1 1¯) and (1 1 0) orientation. Adsorbed sulphate was observed by in-situ STM on the (1 1 0) facets.
Mean field model of a game for power
Abstract Our aim is to model a game for power (equivalent to total energy) as a dynamical process, where an excess of power possessed by a player allows him to gain even more power. Such a positive feedback is often termed as the Matthew effect. Analytical and numerical methods allow to identify a set of stationary states, i.e. fixed points of the model dynamics. The positions of the unstable fixed points give an insight on the basins of attraction of the stable fixed points. The results are interpreted in terms of modeling of coercive power.