Piotr Zelenay

Effect of surface order on adsorption of sulfate ions on silver electrodes

Adsorption of sulfate ions was studied on three basal planes and a polycrystalline surface of silver in 0.1 M HClO4 by radiometric and electrochemical methods. On all four surfaces, adsorption was found to be reversible with respect to the potential and bulk solution concentration of sulfate. Radiometrically determined adsorption isotherms show a clear difference in sulfate adsorption on individual planes. Adsorption of the anion on the basal planes of silver decreases in the sequence: Ag(111)≥Ag(110)>Ag(100). As expected, the polycrystalline silver electrode exhibits intermediate adsorption properties between the most and the least active basal planes. Thermodynamic parameters of adsorption were calculated by fitting the Frumkin isotherm equation to the experimental data points. High values of surface concentration for adsorbed sulfate on the (111) and (110) planes of silver can be accounted for by a match between a tetrahedral structure of the anion and a trigonal distribution pattern of the surface atoms of silver on these planes.

Adsorption of acetic acid on platinum, gold and rhodium electrodes

Abstract The adsorption of acetic acid has been studied on platinum, gold and rhodium electrodes from aqueous electrolytes. On the platinum electrode, the evidences have been presented that in the double layer region of the electrode potentials: (i) the undissociated acetic acid molecule is adsorbed, (ii) the adsorption process is reversible and (iii) the adsorption occurs in the second ad-layer of the interfacial region, ie on the top of the chemisorbed water molecules. In the hydrogen region, the slow (reductive) chemisorption of this compound has been observed. The similarity in the character of the adsorption of acetic acid in the double layer region of the three electrodes investigated have been shown.

Radiochemical Assay of Adsorption at Single Crystal/Solution Interfaces

This paper reports that by using a radioactive labeling method and electrochemistry, results were obtained that show that interactions of bisulfate anion with well-ordered single-crystal electrodes are different from those with the polycrystalline electrodes. In particular, the anion surface concentration on the polycrystalline rhodium electrode increases monotonically with the electrode potential and then decreases when the surface becomes electrooxidized. With Rh(111), the surface stability of bisulfate is observed in a broad electrode potential range. Likewise, the hydrogen adsorption process apparently overcomes a higher energy barrier to nucleate into surface water-bisulfate network on Rh(111) than it does on the polycrystalline surface. These findings, and the corresponding results obtained with platinum electrodes, demonstrate some unique electrochemical properties of electrode materials that have a regular atomic periodicity and a long-range crystallographic order. extension of this work to surfaces covered by underpotential-deposited-metal (UPD) adlayers illustrates the principles of enhanced absorption.

Synthesis and Evaluation of Heat-treated, Cyanamide-derived Non-precious Catalysts for Oxygen Reduction

Although polymer electrolyte fuel cells (PEFCs) have long been recognized as a potential power source for zero-emission vehicles, they remain economically uncompetitive with internal combustion engines. The necessary cost reductions can only be achieved by greatly lowering the content or eliminating the platinum catalyst required for the oxygen reduction reaction (ORR) at the cathode, the electrode process that demands substantially higher Pt loadings than the much faster hydrogen oxidation reaction (HOR) at the anode.

Surface interaction of benzoic acid with a copper electrode

Adsorption of benzoic acid at copper electrodes, obtained by electroplating copper on gold, has been studied in 0.1 M HClO4 using a radiotracer technique and cyclic voltammetry. Impedance spectroscopy has been applied to verify the real surface area of copper electrodes also determined from voltammetric data in the double-layer region. Radiotracer measurements of adsorption have indicated that benzoic acid is surface active on copper in the entire range of potentials available to electrochemical investigation in the perchloric acid solution, ie, from −0.30 to 0.30V (vs. rhe). Adsorption increases with the increase in the electrode potential and bulk concentration of benzoic acid, and reaches saturation at the surface coverage not exceeding 0.30. Exchange of the adsorbate with the bulk benzoic acid molecules is slow but is considerable enough to confirm reversibility of the surface process. Principal thermodynamic parameters of adsorption have been calculated from the experimental surface concentration data using the Frumkin isotherm, found applicable in this case. Benzoic acid molecules are most likely oriented parallel to the surface, with radiotracer data providing no indication of change of that orientation at any potential used in this work. Despite apparent lack of reorientation, benzoic acid adsorption on copper is similar to that on polycrystalline gold, particularly if the rates of the surface process, the Gibbs energies of adsorption and the degrees of the surface/bulk exchange are compared for both systems.

Adsorption of benzoic acid on a polycrystalline gold electrode

Abstract Adsorption of benzoic acid on a polycrystalline Au electrode, obtained by electroplating of gold, has been studied in 0.1 M HClO4 using cyclic voltammetry and radiotracer technique. Adsorption has been found to take place in the entire range of studied potentials, from 0.05 to 1.75 V (rhe), with the surface concentration of the adsorbate exceeding 5 × 1014 molecules cm−2 at saturation. Desorption into a clean supporting electrolyte is small and extremely slow. On the other hand, surface/bulk exchange of benzoic acid is much faster, attesting to the dynamic equilibrium between the adsorbed and solution species. Adsorption data and model calculations strongly indicate that two different orientations of the adsorbed molecules are present on the surface. Flat (parallel to the surface) orientation dominates at less positive potentials while the vertical (perpendicular to the surface) orientation dominates at more positive potentials. Regardless of orientation, benzoic acid adsorption on gold falls into the chemisorption category. General behavior of the system bears close resemblance to the adsorption of benzoic acid on platinum that was reported earlier in Zelenay and Sobkowski, Electrochim. Acta29, 1715 (1984).

The inhibitory effect of some surface active organic compounds on the electrooxidation of strongly adsorbed species derived from HCOOH on polycrystalline platinum

Abstract The effect of dimethylsulphoxide (DMSO), acetonitrile (AN) and acetone (AC) on the adsorption and oxidation of formic acid on platinum electrodes was studied using radiometric and potentiodynamic methods. It was found that formic acid is not adsorbed on the electrode surface previously covered with DMSO, AN or AC. The oxidation of chemisorbed species derived from HCOOH in the presence of DMSO and AN is inhibited because of lowering of the surface concentration of adsorbed water which is an oxidant in the process. The catalytic effect of acetonitrile on the direct oxidation of formic acid on the platinum electrode was higher on smooth than on rough surfaces. The effect was not observed in the presence of DMSO and AC.

Graphene-Riched Co9S8-N-C Non-Precious Metal Catalyst for Oxygen Reduction in Alkaline Media

In this work, a non-precious metal catalyst consisting of Co9S8 nanoparticles surrounded with nitrogen-doped graphene-like carbon (Co9S8-N-C) was developed for oxygen reduction in alkaline media. Improved activity has been measured with the Co9S8-N-C catalyst relative to Pt/C and a non-precious metal catalyst based on Fe instead of Co (Fe-N-C). An extensive physical characterization, including XRD, SEM, TEM, and XPS and electrochemical kinetic analysis was conducted to provide insight into the catalyst morphology and structure.

Interaction of thiourea with silver electrodes

Abstract Adsorption and surface reactions of thiourea on silverized silver electrodes have been studied in 0.1 M HClO4 and 0.1 M NaClO4. Quantitative radiometric data obtained using 14C-labeled thiourea indicate that adsorption of thiourea takes place in the entire range of potentials accessible to surface studies on silver electrodes in the acidic and neutral solutions. The values of the thiourea surface concentration are very high, close to the maximum monolayer packing densities calculated from the molecular size of thiourea (ca. 6 × 1014 molecules cm2). Reorientation of adsorbed molecules from perpendicular to parallel to the surface is a possible reason for the decrease in Г at potentials located on the positive side of the adsorption maximum. As shown by the surface/bulk-exchange experiments, adsorption is reversible in the potential range preceding and directly following the adsorption maximum. In this range, the surface process can be quite accurately described by the Frumkin adsorption model. When corrected for water displacement, the calculated value of the Gibbs energy of adsorption points to strong adsorption of thiourea on silver (chemisorption). At the most positive potentials, surface processes become irreversible, ultimately leading to the formation of chemisorbed sulfur-containing species that act as the electrode poison. Depending on the solution pH, an addition of chloride to the cell has different effects on the adsorption of thiourea. As a result of the Cl−-caused reorientation of the adsorbate, the surface concentration of thiourea increases in the neutral solution. The opposite effect occurs in the acidic solution, where surface blocking by adsorbed chloride plays a dominant role.

Electrosorption of benzoic acid on platinum electrode

Abstract The electrosorption of benzoic acid on platinized electrode was studied by voltammetric and radiometric techniques. The free energy of adsorption, the heterogeneity factor of electrode surface and the surface concentration of adsorbate were determined. The adsorption of benzoic acid may be described by logarithmic isotherms. The kinetics of benzoic acid adsorption was also studied.