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.
Probing Surface Oxide Formation and Dissolution on/of Ir Single Crystals via X-ray Photoelectron Spectroscopy and Inductively Coupled Plasma Mass Spectrometry
Gaining fundamental insights into the formation and the stability of surface oxides on iridium (Ir) surfaces is pivotal to oxygen evolution reaction (OER) electrocatalysis. Herein, we examined the potential-dependent structural and chemical changes occurring on planar Ir(111), Ir(210), and nanofaceted Ir(210) single-crystal surfaces using electrochemistry, scanning probe microscopy, X-ray photoelectron spectroscopy, and inductively coupled plasma mass spectrometry. We show that, after polarization in OER conditions, Ir surface atoms feature mixed oxidation states—(0), (+III), and (+IV)—and then enrich into Ir(+IV) due to the dissolution of Ir(+III) species. The rate of surface and near-surface layer enrichment in Ir(+IV) species depends on the modulation mode of the potential (linear potential sweeps vs. potential steps) and is faster on opened surfaces. By combining fits derived from the XPS spectra and OER activity measurements, we found that the OER specific activity varies with the Ir oxidation state ...
Coverage-dependent infrared spectroscopy of carbon monoxide on palladium(100) in aqueous solution : Adlayer phase transitions and electrooxidation pathways
Infrared reflection−absorption spectra (IRAS) measured for the C−O stretch (νCO) of carbon monoxide dosed on ordered Pd(100) in aqueous 0.1 M HClO4 as a function of the coverage (θCO) and the electrode potential (E) are examined in comparison with extant IRAS and adlayer structural data on Pd(100) in ultrahigh vacuum (UHV). A noteworthy feature of the electrochemical adlayer, as for the UHV system, is the presence of a single νCO band blue shifting markedly (by ca. 100 cm-1) with increasing coverage up to saturation (θCO ≈ 0.8), indicative of uniformly bridging CO coordination. Extrapolation of the θCO-dependent νCO frequencies to surface potentials corresponding to the UHV-based system, however, yielded reasonable concordance only at high coverages. The discrepancies at lower θCO are suggested to arise from solvation effects on the local CO-site surface potentials. Examination of the θCO-dependent νCO peak frequencies ( ), integrated absorbances (Ai), and bandwidth (Δν1/2) for the dosed electrochemical a...