[Show abstract][Hide abstract] ABSTRACT: Pd nanofilms were grown on Au(111) using the electrochemical form of atomic layer deposition (E-ALD). Deposits were formed by repeated cycles of surface-limited redox replacement (SLRR). Each cycle produced an atomic layer of Pd, allowing the reproducible formation of Pd nanofilms, with thicknesses proportional to the number of cycles performed. Pd deposits were formed with up to 30 cycles, in the present study, and used as a platform for studies of hydrogen sorption/desorption as a function of thickness. The SLRR cycle involved the initial formation of an atomic layer of Cu by underpotential deposition, followed by its galvanic exchange with PdCl42– ions at open circuit. The first three cycles were studied using in situ electrochemical scanning tunneling microscopy (EC-STM), which showed a consistent morphology from cycle to cycle and the monatomic steps indicative of layer-by-layer growth. Cyclic voltammetry was used to study the hydrogen sorption/desorption properties as a function of thickness in 0.1 M H2SO4. The results indicated that the underlying Au structure greatly influenced hydrogen adsorption, as did film thickness for deposits formed with fewer than five cycles. No hydrogen absorption occurred for the thinnest films, although it increased linearly for thicker films, producing an average H/Pd molar ratio of 0.6. Electrochemical annealing was shown to improve surface order, producing CVs that strongly resembled those characteristic of bulk Pd(111).
The Journal of Physical Chemistry C 07/2013; 117(30):15728–15740. · 4.84 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: 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 electrochem-ical behaviour after potential cycling of Ir(210) in 0.1 M H 2 SO 4 . 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.
Beilstein Journal of Nanotechnology 08/2014; 2014(5):1349-1356. · 2.37 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The electrocapillary coupling coefficient, ς, measures the response of the electrode potential, E, to tangential elastic strain at the surface of an electrode. Using dynamic electro-chemo-mechanical analysis, we study ς(E) simultaneously with cyclic voltammetry. The study covers extended potential intervals on Au, Pt, and Pd, including the electrosorption of oxygen species and of hydrogen. The magnitude and sign of ς vary during the scans, and quite generally the graphs of ς(E) emphasize details which are less obvious or missing in the cyclic voltammograms (CVs). Capacitive processes on the clean electrode surfaces exhibit ς < 0, whereas capacitive processes on oxygen-covered surfaces are characterized by ς < 0 on Au but ς > 0 on Pt and Pd. The findings of ς < 0 during the initial stages of oxygen species adsorption and ς > 0 for hydrogen electrosorption agree with the trend that tensile strain makes surfaces more binding for adsorbates. However, the large hysteresis of oxygen electrosorption on all electrodes raises the question: is the exchange current associated with that process sufficient for its measurement by potential response during small cyclic strain?
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