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The formation of metal monolayers through underpotential deposition (UPD) depends on the interactions between the electrode surface and the depositing species. Other adsorbable species, if present in the solution, will influence the formation of UPD metal films through their adsorption on the electrode surface, taking place simultaneously. Copper UPD formation on polycrystalline gold surfaces has been investigated in the presence of small amounts of urea, thiourea (TU) and N-substituted thioureas using cyclic voltammetry. The results show that the UPD of copper on gold is significantly influenced by the presence of thiourea in solution. The charge corresponding to the stripping peak obtained in the presence of both Cu2+ and TU in solution is always larger than the sum of the charges resulting when either of them is present alone. Again, the charge observed during stripping in the presence of both Cu2+ and TU is believed to arise from (i) stripping of the UPD Cu, (ii) adsorption–desorption of TU and (iii) oxidation of Cu(TU)n+ complexes. The addition of N-substituted TUs is found to influence the UPD of Cu to different extents. This is tentatively explained in terms of the structure of the organic molecules.

Modification of electrode surfaces with bilayers of organic/inorganic materials is shown to exhibit a variety of functional characteristics. The use of conducting polymers for bilayer construction has recently been explored by various groups. Gold surface has been modified with bilayers of polyaniline and polypyrrole, and the photoelectrochemical and electrochemical characteristics of such bilayer electrodes have been investigated and are reported in this communication.

Prussian Blue (PB) is a polynuclear mixed-valent iron cyanide complex which is zeolitic in nature and has a face-centred cubic structure with a lattice constant of about 10 A [l]. PB-modified electrode surfaces have been the subject of intense study in recent years because of their potential for application in areas such as electrochromism [2,3], electrocatalysis [4,5], photosensing devices [61, charge storage [7,8], ion-selective sensors [9] and semiconducting films [lo-121. Modification of electrodes such as polycrystalline Pt, Au and glassy carbon (GC) with thin PB films using different chemical and electrochemical procedures have been described in the literature [2,7,8,12]. A cyclic polarization procedure for the modification of GC with PB in a neutral medium has been reported in earlier communications [lO,ll]. The PB overlayer has been characterized by in-situ Mijssbauer spectroscopy [13] in order to identify the low spin Fen and the high spin Fe”’ species present in the PB skeleton. In-situ optical absorption spectra on PB-modified SnO, have also been reported in the 400-800 nm region [14]. However, it is desirable to characterize the optical properties of the material over as wide a wavelength range as possible. In the following we present the results of an optical study of PB-modified single-crystal Au and Pt electrodes with special emphasis on the (111) faces of Au and Pt, where the surface redox processes are seen particularly clearly.

Formation of insoluble metal hexacyanoferrate films on chalcogenide semiconductor materials in ferrocyanide medium has been found to be responsible for enhanced photocurrents and inhibition of photocorrosion. Similar beneficial properties recorded by us for the first time on indium hexacyanoferrate in ferrocyanide medium and explained in terms of formation of surface films of composites involving iron hexacyanoferrates are described in this paper.

The oxidation behaviour of methanol on platinum at room temperature in a low concentration of phosphoric acid (≈ 5%) has been studied. Voltammetric behaviour in phosphoric acid medium is compared with that in perchloric acid. The effect of a bismuth underpotential deposition (upd) layer on the oxidation of methanol is also reported.

Prussian Blue (PB)-modified glassy carbon electrodes exhibited stable photocurrents whose polarity was found to depend on the experimental conditions. The photocurrent responses in potassium chloride solutions in the presence and absence of the I−I2 redox system in solution are presented and discussed.