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 Fabrication of Well-Defined Spherical Iridium Nanoparticles and Electrocatalytic Activity towards Carbon Monoxide Adlayer Oxidation
This study outlines the methodology to electrodeposit well-defined iridium nanospheres onto glassy carbon (GC) electrodes at room temperature, using a square wave potential (SWP) technique. Similar work has recently been carried out for other noble metal nanoparticles, in particular platinum and palladium. In this study, particle size and Ir loading can be controlled by altering two key parameters in the electrodeposition process; the nucleation potential and the growth duration. Ir nanoparticles were characterized using cyclic voltammetry (CV) and scanning electron microscopy (SEM). It was found that the nucleation potential and time influence not only the nucleation density but also the particle size. In addition, the electrochemical activity of the particles towards carbon monoxide (CO) adlayer oxidation was investigated as a surface test reaction. The results showed that surface morphology of the deposited particles, which could be altered using potential cycling, plays a pivotal role in determining the activity of the particles. Particles that were treated by potential cycling showed a significantly lower overpotential, in contrast to particles of similar size that were untreated. This indicates an enhancement in electrocatalytic activity due to the enrichment of surface defects.
Surface electrochemistry on an epitaxial palladium film on Pt(111): surface microstructure and hydrogen electrode kinetics
Abstract The surface electrochemistry of adsorbed hydrogen (H upd ) and the kinetics of the hydrogen evolution/oxidation reactions (HER/HOR) have been studied on an epitaxial Pd layer on Pt(111) in 0.05 M H 2 SO 4 in a temperature range of 278–333 K. The morphology and stability of the Pd film during the electrochemical reactions was investigated by means of in situ surface X-ray scattering (SXS). The SXS results show that Pd is deposited onto Pt(111) as a uniform epitaxial metallic layer having the Pt lattice constant, that is, pseudomorphic growth. Due to the strong interaction between the Pd film and adsorbed hydrogen (H upd ), it appears that some of the H upd on Pt(111)Pd may be in the subsurface state. This change in the energetics of the H upd state plays a dominant role in the kinetics of the HER/HOR. The kinetics of the HER/HOR were studied on Pt(111) and Pt(111)Pd by utilizing the rotating disk electrode method. We find significant differences in the electrochemical properties between these two systems, the rate of reaction being much faster on the Pt(111)Pd electrode. We propose that the physical model that appears to rationalize the results for the HER/HOR at low anodic overpotentials on Pt(111)Pd is one which follows application of the Langmuir (ideal) adsorption isotherm for the reaction intermediate (H opd ) and the Volmer–Heyrowsky sequence, the Heyrowsky step being the rds.