It has been realized increasingly that many surfaces and interfacial processes of practical importance are affected significantly by the active metal over layers with rough surface morphology and preferential orientation of some crystalline domains. Smooth metal surface in terms of catalytic and analytic properties for many electrochemical processes are significantly poor or inactive as compared with those of roughened or active metal over layer electrodes. metal over layers can be produced by the processes: 1) Electrodeposition of highly dispersed metal nano-crystals on smooth substrates, (2) From the vapor phase deposition of metals , (3) Chemical processes , In situ formation of highly dispersed metal over layers from the electroreduction of hydrous metal oxide, Formed by high potential anodization of the metallic electrodes.Electrodes activated and roughened by the above-mentioned methods have very versatile applications towards many electrochemical processes. For example, The electrodes roughened by the electrodeposition of metal nano-crystals on smooth substrates play a key role in the determination of analytic and catalytic activities towards many electrochemical processes like oxygen reduction reaction, oxidation of ethylene glycol, simultaneous determination of dopamine and ascorbate, and oxidation of glucose, etc. Vapor phase deposited metal thin films have been used for the ORR in acidic and alkaline media , oxidation of formaldehyde, acetaldehyde and ethanol. Electrodes activated and roughened by chemical processes show a high catalytic effect towards the oxidation of methanol and other organic compounds. Electrodes fabricated by anodization also have potential application towards many electrochemical processes like oxidation of methanol, carbon dioxide, ethanol, glucose, ascorbic acid, and heterocyclic thiazole and reduction of hydrogen peroxide, evolution of oxygen etc. such electrode having active metal over layers enriched in some preferential single crystalline domains with high surface area have supremacy over the electrodes obtained by either of the above processes from (1) to (3) because of their wide applications, easiness of formation, stability, exclusion of the use of extra chemicals and technical difficulties of the other processes.
Electro generated active gold over layers has very versatile application towards the oxidation of Ascorbic acid, Hydrogen peroxide, Uric acid. thus, in this paper , we report formation of active Au over layers on the Au(poly) electrode (agol-Au(poly) electrode) by electro reduction of hydrous Au oxide formed by chronoamperometric technique in acidic media, its characterization using by reductive desorption of S on Au (poly) electrode and oxidative stripping of electrodeposited pb and its electro catalytic activity towards the oxidation of Ascorbic acid, oxidation of Hydrogen peroxide, oxidation of Uric acid. Extensive studies have been done on in situ formation of roughened active metal over layers, enriched in some single crystalline facets, by the electro reduction of hydrous metal oxides. Such in situ produced porous metal over layers with high surface area have very complex topography consisting of metal clusters enriched in some single crystalline domains.
Vassilis Pontikis and Shanmugasundaram Sivarajan,reported as, Surface roughening a common phenomenon observed in the formation of materials is unacceptable for industrial practice, as well as unavoidable. These surface defects are formed during crystal growth or material processing. The formation of disordered surface phases and topologically induced phase transitions are expected for purely entropic reasons. Surface roughening, faceting, and surface melting are all phase transitions involving the formation of various topological imperfections. Crystal shape and crystal growth rate are significantly influenced by this phenomenon. In the last decade, with the development of sophisticated experimental methods and computer simulation with higher speeds, a wide variety of experimental studies of surface roughening process have been carried out.
L.D Burke et al. studied hydrous Au oxide in terms of its formation , stability and applications. Yu-Chuan Liu, Chee-Chan Wang, Chun-En Tsai reported as, the effects of electrolytes used in roughening gold substrates by electrochemical methods on surface-enhanced Raman scattering (SERS) were first investigated. First, gold substrates were roughened by triangular-wave oxidation–reduction cycles (ORC) in aqueous solutions containing different kinds of 0.1M electrolytes. Then Rhodamine 6G (R6G) was used as Raman probe to examine this effect of electrolytes used on the SERS observed. The result indicates that the highest intensity of SERS of R6G was obtained on the roughened Au substrate prepared in 0.1M NaCl, which was less used in the literature. Meanwhile, it was also found that the rougher surface morphology observed, which is contributive to the higher SERS obtained, is corresponding to the smaller cathodic peak area shown in the cyclic voltammograms for roughening the Au substrate. A.J. Arvia et al. conducted studies on columner growth of hydrous Au oxide, elipsometric experiments on the formation of hydrous Au oxide layers, STM-SEM and impedance studies on the characterization and mechanism of growth mode of hydrous Au oxide, surface diffusion of Au atoms ,change in the polycrystalline Au surface and kinetics.
Vojtěch Hrdlička, Tomáš Navrátil, Jiří Barek, Jiří Ludvík reported as, The electrochemical behavior of polycrystalline gold electrode (PAuE) modified by self-assembled monolayers (SAMs) of thiolated calixarene (C4A) and undecanethiol (C11) was investigated by voltammetric methods and electrochemical impedance spectroscopy.Coverage of the thiol SAMs and their stability was tested. The C11 layer is very stable; the desorption peak was recorded only in basic solutions of pH 12 and higher (at −1.30 V vs. Ag|AgCl (3 mol L−1 KCl)).The position of the C4A desorption peak is more pH dependent and it was recorded at −1.08 V at pH 13. Molecular coverage for C4A and C11 SAMs modified PAuE is 364 ± 52.9 μC cm−2 and 137 ± 20.0 μC cm−2 respectively. The properties of the PAuE modified by C11 and/or C4A were investigated using the model compounds hydroquinone, ferrocene and potassium ferrocyanide. It is assumed that the oxidation of the hydroquinone cannot be realized inside the C4A cavity because the hydroquinone molecule is too big to enter the cavity. Similar behavior was observed using potassium ferrocyanide. In contrast, cyclic voltammograms of ferrocene oxidation were only negligibly affected by the electrode modification. Moreover, capacitance measurements proved accumulation of ferrocenium ions at the C4A modified electrode. Juodkazis et al. carried out ZPS and cyclic voltammetric studies on the hydrous Au oxide over layers for characterization and determination of surface Au atom concentration
For cyclic voltammetric measurements, Au (poly) electrodes (1.6 mm, sealed in a Teflon tube) with an exposed surface area of 2.01×10-2 cm2 were used as working electrode. A spiral Pt wire and an Ag|AgCl|KCl (sat.) were the counter and reference electrodes, respectively. A conventional two-compartment Pyrex glass cell was used. Prior to each measurement, N2 gas was directly bubbled into the cell for 30min to obtain N2-saturated 0.1M NaOH solution and during measurement N2 gas was flushed over the cell solution. All the measurements were performed at 25±1◦C. The Au (poly) electrodes were polished with aqueous slurries of successively finer alumina powder (down to 0.06 cm2) and were sonicated for 10min in Milli- Q -water. The Au(poly) electrodes were then electrochemically pretreated in 0.05 M H2SO4 solution by repeating the potential scan in the range of −0.2 to 1.5 V vs. Ag|AgCl|KCl(sat.) at 0.1 Vs-1 for 10min or until the cyclic voltammetric characteristic for a clean Au (poly) electrode was obtained. A roughness factor (rf) of 1.2was estimated for the Au (poly) electrodes as calculated from the charge consumed during the formation of surface oxide monolayer using cutting-weighing technique.Activation of Au(poly) electrode was accomplished by using chronoamperometry.