Tadeusz Hepel

Morphology and Composition of Electrodeposited Cobalt‐Zinc Alloys and the Influence of Boric Acid

The morphology and composition of cobalt‐zinc alloys electrodeposited on a Pt rotating disk electrode were investigated. Three unique morphologies have been identified by scanning electron microscopy and the composition of each characterized by solid‐state stripping voltammetry. The effect of boric acid on the morphology of the surface films was also investigated. The results indicate that addition of boric acid to the plating bath increases the nucleation density of the deposit and increases the content of Zn in the alloy. The current efficiency for the deposition process is also enhanced in the presence of boric acid. These effects have been attributed to the adsorptive interactions of boric acid at the electrode surface.

Influence of Boric Acid on Electrodeposition and Stripping of Ni‐Zn Alloys

The effect of boric acid on the electrodeposition and potentiodynamic stripping behavior of Ni‐Zn alloys was investigated using Pt rotating disk electrode. At low Zn(II) concentrations, boric acid raised the current efficiency of the deposition process and at higher Zn(II) concentrations, an increase in the Ni content of the deposited alloy was observed. In the presence of boric acid, a considerable change in the primary nucleation rate and suppression of the secondary nucleation processes on the alloy surface have also been observed. All these effects have been attributed to the adsorptive interactions of boric acid.

Chlorine Evolution and Reduction Processes at Oriented Single‐Crystal RuO2 Electrodes

RuO/sub 2/ single-crystal electrodes have been used to study the mechanism of the chlorine evolution/reduction reactions. RuO/sub 2/ (110) and (101) surfaces show the same anodic Tafel slopes equal to 40 mV/decade. Significant differences in the electrocatalytic behavior of these two surfaces were found for the chlorine reduction reactions. Two cathodic voltammetric peaks at E = 780 and E = 220 mV vs. SCE reference were observed for the RuO/sub 2/ (110) electrodes. The peak at E = 780 mV is completely suppressed in case of the RuO/sub 2/ (101) electrodes. It is suggested that the natural oxygen sites that are available only on the ideal (110) surfaces provide active centers for the formation of surface O.Cl/sup +/ groups that are intermediates in the Krishtalik mechanisms. The cathodic LSV peak at E = 780 mV observed only for the RuO/sub 2/ (110) surfaces indicates, then, the reaction path with chloronium intermediates. The influence of the surface ruthenium oxide rearrangement processes on catalytic activity of the electrode and possible changes in the reaction mechanism are discussed in detail.

Diagrams of electrochemical equilibria of the system copper-potassium ethylxanthate-water at 25°C

Abstract On the basis of thermodynamic calculations, diagrams of metastable electrochemical equilibria of the system copper-potassium ethylxanthate-water, at 25°C were constructed. The equilibria equations and diagrams for the total activity of [EtX−] + [HEtX] + 2 [(EtX)2] (equalling 10−1, 10−4 and 10−7 mol/dm3), are presented. The practical conclusions resulting from these diagrams for the flotation of native copper are discussed.

Irreversible Voltammetric Behavior of the (100) IrO2 Single‐Crystal Electrodes in Sulfuric Acid Medium

The electrochemical behavior of (100) single‐crystal electrodes in has been studied using linear potential scan cyclic voltammetry. A highly irreversible behavior of the main electrochemical process of hydrogen or hydronium ion injection/ejection has been found in the potential range 360–580 mV (vs. reference). The obtained voltammograms have been compared with those for single crystals possessing similar electrocatalytic properties and the same crystallographic structure and also with the behavior of sputtered and anodic films. It has been found that the energy of major interaction of hydrogen species with the single‐crystal structure is close to that observed for sputtered films but differs by ca. 29 kJ/mol (corresponding to 300 mV in the potential scale) from that for the anodic films. The penetration depth for hydrogen is highly minimized in the case of single‐crystal electrodes and involves at most one or two monolayers. Thus, the coloration/bleaching process described for the IROX films cannot develop on nonhydrated single‐crystal electrodes unless their crystallographic structure is damaged by cycling in a wide potential range.

Thermodynamic and Photoelectrochemical Behavior of the n ‐ TiO2 Electrode in Fluoride‐Containing Solutions

Abstract : Diagrams of the stable and metastable electrochemical equilibria for the system Ti - HF - H20 at 25 C have been constructed. Increased solubility of titanium dioxide in fluoride containing solutions has been found to occur over a narrow range of solution pH near 3.2. On the basis of the thermodynamic diagrams, appropriate conditions for etching n-Ti02 semiconductor electrodes were chosen. The etching solutions prepared for the n-Ti02 semiconductor electrodes showed very good surface-cleansing properties. A photoetching process under anodic bias is recommended for the preparation of the n-Ti02 surface for the purpose of use in solar energy converters. The doping profile in the space-charge layer which forms during the photoetching treatment is more effective for splitting the electron-hole pair created in a working electrochemical solar cell. Photocurrent-voltage characteristics obtained for n-Ti02 electrodes in F- solutions do not fit the Butler-Gartner equation, since the Butler-Gartner equation does not correctly describe photoeffects on medium and heavily doped semiconductor electrodes. From the chronovoltamperometric and coulometric study of the reactions taking place at electrode potentials negative of the flat-band potential, only the first step of the Ti02 reduction to lower oxides is reversible. (Author)

Chloride interference with non-stoichiometric copper sulphide coppers-selective electrodes : Part 1. Mechanisms

Abstract The behaviour of copper(II)-selective electrodes made of non-stoichiometric copper sulphide single crystals is discussed. The mechanism of chloride ion interference with the electrode operation is considered on the basis of potentiometric and dynamic measurements. The occurrence of irreversible processes at the electrode surface is described.

The anodic dissolution of chalcocite in an ammoniacal environment

Abstract Presented is the proposed model for the mechanism of anodic oxidation of the semiconductor mineral chalcocite in an ammoniacal environment. The kinetic parameters of the process αa, ks, j00, the formal potential and the electrochemical order of the reaction in relation to ammonia are given.

Chloride interference with non-stoichiometric copper sulphide copper(II)-selective electrodes : Part 2. Exact determination of the chloride interference region

Abstract A general equation for calculating the limit of the ligand interference region with the non-stoichiometric copper sulphide single-crystal electrode is described. The critical ligand concentration can be computed for a preselected maximal error in copper(II) ion determinations. The effect of the composition of the electrode material is discussed. The experimental results for the chloride interference show good agreement with theoretical predictions.

Chloride interference with non-stoichiometric copper sulphide copper(II)-selective electrodes: Part 3. New equation for the electrode response

Abstract A general equation for the electrode potential response under metastable equilibrium conditions is derived for the non-stoichiometric copper sulphide electrodes immersed in solutions containing Cu(II) and Cu(I) and the interfering chloride ions. The theoretically predicted “anomalous” slopes (SII = δ E/δ) log CCu(II) of the calibration curves, greater than 29.6 mV at 25° C, were confirmed experimentally in concentrated chloride solutions. The inapplicability of the Nicolsky equation for the electrodes at equilibrium is discussed on the basis of the theory presented. The new relationship (Eqn. 13) can be adapted for other ion-selective electrodes for which the exchange reactions with the solution species are fast enough and mass transport is not inhibited.