Abstract:Ex situ and in situ STM characterization of the electrode materials, including HOPG, GC, Au, Pt and other electrodes, is briefly surveyed and critically evaluated. The relationship between the electrode activity and surface microtopography is discussed.
“…Both roughening and smoothing have been reported. More recently, potential-induced reconstructions have been revealed in extenso by STM (see, for instance, the review articles by Kolb, Gewirth and Niece, Li and Wang, and Moffat).…”
It has been emphasized in several studies that the state of the surface, including the surface roughness, is very important for the reproducible formation of high-quality self-assembled monolayers on gold. The pulsed-potential pretreatment procedure described in this paper can, in a reproducible way, reduce the surface roughness of mechanically polished polycrystalline gold electrodes by a factor 2. The developed procedure, in which the gold is alternately oxidized and reduced, has been optimized for use in a flow system (100 mM phosphate buffer pH 7.4). The influence of the pretreatment procedure on the surface roughness of the electrodes has been studied by in-situ oxygen adsorption measurements using cyclic voltammetry. The most effective pulse regime in producing a gold surface with a reproducible and relatively low surface roughness is a triple-potential pulse waveform, with potentials of +1.6, 0.0, and -0.8 Vvs SCE and pulse widths of 100 ms for each potential. Prolonged pulsing for 2000-5000 s with the gold working electrode in a flow-through cell showed an electropolishing effect, i.e., a decrease of the roughness in time. Flow conditions are very important: the roughness decreased faster at higher flow rates, while an increase was observed without flow. A process of reconstruction and dissolution of gold during application of the potential pulses under flow conditions is assumed to account for the observed phenomena. A self-assembled monolayer of thioctic acid with reproducible characteristics, determined with impedance measurements, could be formed on a pretreated gold surface.
“…Both roughening and smoothing have been reported. More recently, potential-induced reconstructions have been revealed in extenso by STM (see, for instance, the review articles by Kolb, Gewirth and Niece, Li and Wang, and Moffat).…”
It has been emphasized in several studies that the state of the surface, including the surface roughness, is very important for the reproducible formation of high-quality self-assembled monolayers on gold. The pulsed-potential pretreatment procedure described in this paper can, in a reproducible way, reduce the surface roughness of mechanically polished polycrystalline gold electrodes by a factor 2. The developed procedure, in which the gold is alternately oxidized and reduced, has been optimized for use in a flow system (100 mM phosphate buffer pH 7.4). The influence of the pretreatment procedure on the surface roughness of the electrodes has been studied by in-situ oxygen adsorption measurements using cyclic voltammetry. The most effective pulse regime in producing a gold surface with a reproducible and relatively low surface roughness is a triple-potential pulse waveform, with potentials of +1.6, 0.0, and -0.8 Vvs SCE and pulse widths of 100 ms for each potential. Prolonged pulsing for 2000-5000 s with the gold working electrode in a flow-through cell showed an electropolishing effect, i.e., a decrease of the roughness in time. Flow conditions are very important: the roughness decreased faster at higher flow rates, while an increase was observed without flow. A process of reconstruction and dissolution of gold during application of the potential pulses under flow conditions is assumed to account for the observed phenomena. A self-assembled monolayer of thioctic acid with reproducible characteristics, determined with impedance measurements, could be formed on a pretreated gold surface.
“…However, there are also plenty of examples where specific area, or “total active surface area”, was used instead. In this case, the electrode surface was defined as a three-dimensional object, with significant surface roughness. ,,,− For example, it was demonstrated that the amount of adsorbed material on the electrode surface depends on the electrode conditions (surface roughness). 1 AFM images (2.20 μm × 2.20 μm) show the characteristic surface morphology for different carbon electrode substrates: (a) Highly oriented pyrolitic graphite (HOPG), (b) Fractured vitreous carbon (FVC) and (c) Mechanically polished vitreous carbon (MPVC). 2 Cyclic voltammograms for the Ag(NH 3 ) 2 + deposition process obtained onto HOPG, FVC, and MPVC electrodes, from 10 -2 M Ag(NH 3 ) 2 + /1.6 M NH 3 , 1 M KNO 3 electrolyte solution.…”
Section: Resultsmentioning
confidence: 99%
“…In this case, the electrode surface was defined as a three-dimensional object, with significant surface roughness. 17,21,24,[36][37][38] For example, it was demonstrated that the amount of adsorbed material on the electrode surface depends on the electrode conditions (surface roughness).…”
The influence of the electrode surface quality and surface morphology on the silver electrocrystallization process onto a carbon substrate from 10 -2 M Ag(NH 3 ) 2 + /1.6 M NH 3 , 1 M KNO 3 (pH ) 11) electrolyte solution was studied. Three substrates with different types of surface morphology and surface roughness were used: highly oriented pyrolitic graphite (HOPG), mechanically polished vitreous carbon (MPVC), and fractured vitreous carbon (FVC). Before the silver deposition process, the electrode surface was examined and characterized by means of Atomic Force Microscopy (AFM) analysis. Evaluation of the kinetic parameters of the silver nucleation and the growth behavior, as well as other characteristics of the silver electrocrystallization process onto carbon substrates, were based on cyclic voltammetry and chronoamperometric measurements. Cyclic voltammetry data also show that silver deposition efficiency is proportional to the increase of electrode surface roughness (from HOPG, via MPVC to FVC). The silver bulk deposition process on all three carbon substrates was characterized as 3D nucleation and diffusion-controlled growth. However, this process proceeds with different overpotentials on different substrates: the lowest for HOPG and the highest for MPVC electrode surface. The major electrocrystallization parameters, such as nucleation rate, number of active sites, and number of formed silver nuclei, strictly related to the electrode surface conditions, seem to not follow the same trends as the cyclic voltammetry data. It is clearly indicated in the nonlinear relationship between number of active sites and the surface features (recognized in AFM images). As pointed out in the discussion, it opens new questions regarding the nature of the active sites for deposition on the electrode surface and their identification by microscopic techniques.
“…Scanning tunneling microscopy (STM) provides an excellent tool for these studies, because it can operate in situ to examine the electrode/electrolyte interface. [15][16][17] Although electrode materials such as Pt, Au, and graphite have been largely investigated by STM, 15 its use to the study of metal oxides is not so frequent. 18 Investigations of SnO 2 -based materials by STM or atomic force microscopy (AFM) have been reported.…”
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