I. Bakos

Adsorption of cinchonidine on platinum: an electrochemical study

The adsorption of cinchonidine (CD) on polycrystalline platinum surfaces in 0.5 mol dm−3 H2SO4 has been investigated. It has been found that adsorption is irreversible, desorption takes place at relatively high potentials simultaneously with the oxidation of CD molecules. According to our results CD covers only a part of the Pt surface and maximal coverage is influenced by the surface structure. Some assumptions for the site requirement of an adsorbed CD molecule have also been made.

Experimental evidence demonstrating the occurrence of reduction processes of ClO4− ions in an acid medium at platinized platinum electrodes

Abstract It has been shown that an unexpected cathodic current appears during some cyclic voltammetric, voltradiometric and transient measurements at platinized electrodes carried out in the presence of HClO4 supporting electrolytes. The distortion of voltammetric behaviour depends strongly upon the concentration of HClO4 and the sweep rate. The observed phenomena can be almost completely eliminated by addition of HSO4− or Cl− ions to the solution phase. Radiotracer adsorption studies show that the adsorption of these anions plays a dominant role in the inhibition process. The phenomena observed are explained by the assumption that the reduction of adsorbed ClO4− ions takes place in a wide potential range under certain experimental conditions.

Study of the relationship between voltammetric behaviour and electrocatalytic activity in the reduction of ClO4 - ions at platinized platinum electrodes

Cyclic voltammetric measurements were carried out with various Pt/Pt electrodes in 3 mol dm−3 HClO4 and 0.5 mol dm−3 H2SO4 electrolytes in order to find a relationship between their voltammetric behaviour in H2SO4 and their activity for the electrocatalytic reduction of ClO4− ions. It was found that the catalytic activity of a platinized electrode, in the reaction studied, depends strongly on the parameters of the platinization method used in its preparation. However, this behaviour cannot be correlated with the height or position of the hydrogen adsorption peaks observed in H2SO4 solution as very different catalytic activity was found in the case of almost similar voltammetric behaviour. It was shown that alternating anodic-cathodic treatments (between 0.05 and 1.4 V) of the various electrodes “equalize” their voltammetric behaviour and at the same time minimize their electrocatalytic activity. This phenomenon explains why the electrocatalytic reduction of ClO4− ions escaped the attention of many workers.

An experimental study of the relationship between platinization and the shape of the voltammetric curves obtained at Pt/Pt electrodes in 0.5 M H2SO4

The voltammetric behaviour of various platinized platinum electrodes in an H2SO4 (0.5 mol dm−3) supporting electrolyte was studied in order to investigate the effect of the platinization technique on the shape of the voltammetric curves. A wide variety of voltammetric behaviours was found depending on the platinization conditions in the case of the galvanostatic deposition method. Similarity to the results obtained by fast repetitive potential perturbation of smooth electrodes is demonstrated.

Electrochemical adsorption of rhodium on platinum

Electrosorption of rhodium on a polycrystalline platinum surface has been studied. It has been found that a complete Rh-coverage can be obtained by spontaneous adsorption via the ionization of preadsorbed hydrogen. Underpotential deposition of rhodium has been observed both in 0.5 M H2SO4 and 0.2 M HCl supporting electrolytes. The value of the underpotential shift was found to be about 100–120 mV.

Electroreduction of rhenium from sulfuric acid solutions of perrhenic acid

The electrodeposition of rhenium species from sulfuric acid solutions of ReO4− ions onto polycrystalline Pt and Au surfaces has been studied. The experimental results suggest that ReO2 adsorption takes place and after completion of ReO2 adsorption bulk phase ReO2·xH2O and ReO3 deposition can be observed. From a higher than 10 M sulfuric acid solution of ReO4− ions only Re2O5 can be electrodeposited. In diluted H2SO4 or water media Re2O5 decomposes and ReO2 is formed.

Electrocatalytic reduction of ClO4- ions at an electrodeposited Re layer

Abstract The reduction of ClO 4 − ions was studied in an acid medium at Re layers electrodeposited onto Pt and Au supports from ReO 4 − -containing supporting electrolytes. It was shown that the electroreduction leading to the formation of Cl − ions takes place in a relatively wide potential range (0–300 mV /RHE); however, no real steady state polarization measurements could be carried out owing to the self-inhibition caused by adsorption of the reduction product (Cl − ion) and the change of the surface state of the electrode. The role of the competitive adsorption of anions was demonstrated by a radiotracer study of the adsorption of labelled HSO 4 − ions. The problems connected with the interpretation of the experimental results are discussed.

Investigation of ruthenium deposition onto a platinum electrode in hydrochloric acid media

Abstract Ruthenium deposition onto the Pt surface has been investigated in 0.5 M HCl and it was shown that the Ru coverage formed via ionization of pre-adsorbed hydrogen does not depend on the Cl− ion activity. It is strongly dependent, however, if the deposition is carried out at a rather positive potential. The ratio of hydrogen adsorbed on Ru and Pt surfaces of the same area (HRua/HPta = 0.15) and the site requirement of an adsorbed Ru atom (S = 1.8) have been determined. A mechanism for Ru deposition via ionization of hydrogen adsorbed on platinized Pt is proposed and it is suggested that the Run+ + ne− → Ru process is slow compared to transport processes and adsorption.

Influence of deposition potential on the voltammetric behaviour of potentiostatically formed platinized electrodes

Abstract The voltammetric behaviour of platinized electrodes in relation to their formation potential was studied (deposition from H 2 PtCl 6 solution). It was found that the ratio of the heights of the two most characteristic hydrogen peaks appearing on the voltammograms obtained in 0.5 mol dm −3 H 2 SO 4 depends on the potential of the formation of the electrode exhibiting one or two singularities, depending on the composition of the platinizing solution. It is shown that within a certain range of parameters a preselected pattern in the voltammetric behaviour of platinized electrodes with high real surface area (roughness factor values up to 600–800) can be realized by choosing an appropriate condition for the platinization.

Investigation of the electrodeposition and behaviour of Re layers by coupled radiochemical and electrochemical methods

The electrodeposition of Re from ReO4− species dissolved in HClO4 and H2SO4 supporting electrolytes and the behaviour of the electrodeposited layers were studied by coupling electrochemical methods with the measurement of the β− radiation backscattered by the layer. Factors influencing the electrocatalytic activity of Re in the reduction of ClO4− ions were studied.