Redox processes taking place at precipitated hydrous iron hydroxide layers chemically formed on platinum substrates in sodium hydroxide solutions are investigated at 25 ~ C. The electrochemical behaviour of these layers depends considerably on the electroreduction level reached in chargedischarge cycles. The accumulation of Fe 304 during oxidation-reduction cycles can produce an increasing irreversibility of the Fe(II)/Fe(III) redox couple. Data are compared to results obtained with iron hydroxide layers formed by electrochemical and chemical methods on massive iron electrodes. Results are discussed in terms of a composite structure for the iron hydroxide layers.

Aluminium electrodeposition from ionic liquids (ILs) prepared using a novel structure composed by perfluoro-3-oxa-4,5 dichloro-pentansulphonate [CF2ClCFClOCF2SO3-] and different cations is presented. The novel anion was designed by Solvay Specialty Polymers with the purpose to confer to the ionic liquids strong hydrophobic properties that facilitate the aluminium deposition in ambient conditions. Three cations, imidazolium, pyridinium and guanidinium are used to prepare the corresponding three liquids. In water, the resulting liquids prepared with imidazolium and pyridinium show very low miscibility and the liquid prepared with guanidinium is insoluble. Their electrochemical windows are dependent of both the cations and the substrate nature and are sufficiently wide to allow aluminium deposition. Even so, it was evidenced that the reduction of the new structure is not especially difficult. The AlCl3 was selected as useful source of Al(III) electroactive species to obtain coherent deposits. Using aluminium hydroxide, the coalescence of the aluminium deposits was not achieved. The viability of aluminium electrodeposition was, at first, tested on vitreous carbon, demonstrating it follows through a nucleation and growth process. As the practical interest carries to the use of metallic substrata, nickel was selected to analyse deposition process. The deposits prepared at constant current showed a better appearance, less stressed and smoother than the ones prepared at constant potential. The effect of temperature and concentration was studied in solutions prepared with tetramethyl guanidinium-perfluoro-3-oxa-4,5 dichloro-pentansulphonate, taking advantage of its immiscibility in water. Deposits prepared from the lower concentrations tested (AlCl3:IL 0.95:1 molar ratio) were continuous, fine grained and stress-free, provided that they were obtained at moderate applied current. From higher Al(III) concentration solutions it was only possible to allow stress-free deposits by applying low currents. Highlights Aluminium electrodeposition from a new hydrophobic solvents.  Hydrophobic anion and work temperature allow deposition process in ambient conditions.  Preparation under constant applied current favours stress-free deposits versus potentiostatic deposition.  Stress is minimized by tailoring applied current, AlCl 3 content and temperature.

The surface changes produced on Au in HF solutions by applying relatively fast periodic potentials are investigated. The range of frequency and potential limits can be adjusted to produce principally either transient activation for the hydrogen electrode reaction (HER) or electrochemical faceting. The first effect is largely independent of the second one, as it implies the development of a transient surface structure which facilitates hydrogen adsorption and absorption. Electrochemical faceting caused by oxidationreduction cycles (ORC) depends on the potential limits which are associated with either Au electrodissolution and electrodeposition or Au oxide electroformation and electroreduction. Electrochemical faceting can be clearly seen through SEM micrographs, and the type of preferred orientation can be tentatively inferred from voltammetry of underpotential deposition (upd) of Pb in 10'3 M Pb(C104)2 + 1 M HC104 solution through a direct comparison with data reported in the literature for the reaction on single-crystal Au surfaces. Electrochemical faceting implies a simultaneous increase in surface roughness, as followed from changes in voltammetric charges for both upd Pb and 0 atom electrodesorption in acid solutions.