The temperature coefficient of the potential of zero charge of Ag single crystal face electrodes in aqueous electrolyte solution

The temperature coefficient of the potential of zero charge of Ag single crystal electrodes, dEσ₌₀/dT , was measured by recording capacitance curves at different temperatures. Two experimental approaches were adopted: the “continuity” and the “discontinuity” method, consisting in recording curves at different temperatures without and with extraction of the electrode from the solution, respectively. Appreciable differences have been observed. The origin of the differences and their significance are discussed in terms of keeping the appropriate conditions for the electrode/solution interface during the experiments.На основі даних для ємності при різних температурах отримано температурний коефіцієнт потенціалу нульового заряду срібних моно-кристалічних електродів. Застосовано два типи експериментів: метод “неперервності” і “розривності”, що полягає в записі кривих ємності при різних температурах без і з виділенням вкладу електрода в розчині відповідно. Виявлена суттєва різниця в результатах, походження і важливість якої досліджується при відповідних умовах експериментів для поверхні розділу електрод-розчин

Examination of RuO2 single-crystal surfaces: charge storage mechanism in H2SO4 aqueous solution

Systematic voltammetric and impedance studies of RuO2 ‘as-grown’ single crystals were carried out using the (101), (110) and (002) faces in 0.5 mol dm-3 sulphuric acid solution and applying the hanging electrolyte meniscus technique. The crystal surfaces, prepared by the vapor transfer technique at high temperature, show well-defined XRD patterns. The dependence of the voltammetric characteristics on potential scan rate modulations was investigated. The charge storage mechanism was examined in the following cases for differences: (i) in the anodic surface charge qa* and the atomic distribution of ideal surfaces, (ii) between the total anodic charge qa*tot and the anodic charge associated with the electrochemical process qa** due to the redox couple in the solid state. A systematically higher charge for the (101) face in the same potential range represents a probe for the crystal face specificity of the redox process

Adsorption of C-5 nitriles at liquid-metal electrodes. A comparison of adsorption parameters for isovaleronitrile at the polarized surfaces of Mercury and Indium-Gallium alloy (eutectic composition)

In this paper a quantitative study of the adsorption of iso-C4H9CN(isovaleronitrile, IVN) at the interfaces between Hg and In-Ga alloy (eutectic composition) electrodes and aqueous solutions is described. The equilibrium charge densities at Hg electrodes were determined from both electrocapillary and impedance measurements, whereas at the In-Ga electrode only impedance data were available. The adsorption parameters for IVN, including the standard Gibbs energy of adsorption (DGads°), the lateral interaction parameter, a, and the limiting Gibbs surface excess were calculated and compared with previous data relative to the behavior of aliphatic compounds at different interfaces. The experimental results are discussed in terms of metal-solvent and metal-adsorbate interactions

Specific adsorption of bromide and iodide anions from nonaqueous solutions on controlled-surface polycrystalline silver electrodes

A systematic study was performed on the specific adsorption of bromide and iodide anions on controlled-surface polycryst. Ag electrodes, from 3 org. solvents (acetonitrile (ACN), propylene carbonate (PC), and DMF), combining differential capacity and impedance expts. with a recently proposed indirect voltammetric method based on the monitoring of the neg. shift of the redn. peak potential of a probe org. halide mol. induced by progressive addns. of halide anions, resulting in increasing adsorption competition. Bromide and iodide ions are specifically adsorbed onto polycryst. Ag electrodes in the 3 org. solvents studied. The adsorption process, which is slow and it is characterized by a partial charge transfer and by a slow diffusion step, is modulated by the different coordination abilities of the solvents for the species involved in the adsorption. The 3 exptl. methods provide consistent results. In particular, the strength of halide adsorption increases in the halide sequence Br- < I-, and in the solvent sequence ACN < PC < DMF

Studying electron transfer reaction at the Au/n-decanethiol/aqueous solution of NaNO3 interface by electrochemical impedance spectroscopy

The electrochemical behavior of the gold/electrolyte interface in aqueous 1 M NaNO3 solutions in the presence of an organic monolayer of n-decanethiol (CH3(CH2)9S) is studied by electrochemical impedance spectroscopy in the frequency range of 10-10 5 Hz and also by cyclic voltammetry. It is experimentally shown that in the potential interval from 0 to -0.5 V (vs. SCE), the dense monolayer film decreases the measured current density approximately 40-fold. The measured capacitance falls down to 1-2 \u3bcF/cm2. Based on the analysis of impedance characteristics acquired with the use of empirical equivalent circuits comprising ideal and nonideal analogues of electric circuits, the tentative estimates of the thickness of organic monolayers formed on Au electrodes with various roughness factors are obtained. Using the complex nonlinear regression (CNLS) method and a model of microarray electrode, the porous structure of adsorbed monolayers is revealed and the transition frequency of interfaces under study is determined. The degree of inhibition of the electron transfer across the Au/n-decanethiol/solution interface is determined by comparing the rate constants for the Ru[(NH3)6]3+/2+ redox process on clean and modified electrodes

Adsorption competition effects in the electrocatalytic reduction of organic halides on silver

A systematic study of {silver|inorg. and/or org. halide} interphases is described, based on cyclic voltammetric and impedance expts. carried out on polycryst. electrodes of high reproducibility (controlled by comparison with monocryst. ones), in H2O and in MeCN. The adsorption competition is brought into focus (i) between the 3 inorg. halides Cl-, Br-, and I-, with the possible interference of ions from the supporting electrolyte, and (ii) between org. and inorg. halides, esp. iodides. Actually adsorption competition proves to be a detg. factor in the electrocatalytic mechanism (a remarkable threshold effect being obsd. for the redn. potentials of org. bromides in correspondence with the limiting neg. potential for iodide anion adsorption). Vice versa, the variation of the redn. potentials of a given reacting mol. with the background electrolyte provides significant clues on the nature of the specifically adsorbed species

Acetonitrile as Adsorbate or Solvent to Probe the Crystal Face Specificity of Metal-Water Interaction at Silver Electrode/Solution Interfaces

The crystal face specificity of metal–water interaction at Ag electrode/solution interfaces is investigated by using acetonitrile (ACN) as a probe molecule of the water interfacial structure or as a solvent in which water is a solute. Capacitance and voltammetric curves suggest that ACN is weakly adsorbed from aqueous solution on Ag in the order (111) > (100) > (110). Apparent inconsistencies of adsorption parameters are explained by the occurrence of two ACN adsorption modes: (i) directly on the metal surface and (ii) on the water layer adsorbed on the metal surface. Ag surface oxidation in ACN in the presence of variable amounts of water suggests that water has an inhibiting effect on Ag oxidation, the diminution of the water content in ACN leading to free anodic dissolution of the metal surface

Electron transfer across the interface gold/self-assembled organic monolayer : comparison of single- and two-component systems

Single- and two-component self-assembled organic monolayers (SAM) formed of HS-C 10H 20- COOH and the HS-C 10H 20-COOH + HS-C 6H 12-OH mixture and applied on gold electrodes of different shapes and roughness are studied. The resulting monolayers are characterized in 1 M NaNO 3 solutions by the methods of electrochemical impedance spectroscopy in the frequency range from 1 Hz to 100 kHz and cyclic voltammetry in the potential range from 0 to -0.4 V (SCE). Using these method, the behavior of modified single-crystal and polycrystalline gold electrodes in electrolyte solutions of different acidity is assessed and the standard rate constants for the Ru[(NH 3) 6] 3+/2+ redox reaction are determined. The SAM film formed from the ethanol solution of the HS-C 10H 20-COOH + HS-C 6H 12-OH mixture (0.025 M) on the Au(210) single-crystal face lowers down the rate of the heterogeneous Ru[(NH 3) 6] 3+/2+ reaction from 1.5 to 4.02 7 10 -4 cm/s in the electrolyte solution with pH from 2. In solutions with higher pH, the rate constant is higher by almost an order of magnitude (2.74 7 10 -3 cm/s). The distribution of micropores in SAM films is studied within the framework of a model of micro-array electrodes. The results of studies are compared with the literature data on the gold electrode in solutions of inactive electrolytes in the absence and in the presence of SAM films formed by alkylmercaptans with equal chain lengths

Building up an electrocatalytic activity scale of cathode materials for organic halide reductions

A wide study on the electrochem. activity of 4 model org. bromides was carried out in MeCN on 9 cathodes of widely different affinity for halide anions (Pt, Zn, Hg, Sn, Bi, Pb, Au, Cu, Ag), and the electrocatalytic activities of the latter were evaluated with respect to 3 possible inert ref. cathode materials, i.e. glassy C, B-doped diamond, and fluorinated B-doped diamond. A general electrocatalytic activity scale for the process is proposed, with a discussion on its modulation by the configuration of the reacting mol., and its connection with thermodn. parameters accounting for halide adsorption