V. Daujotis

The mechanism of electroreduction of silver cyanide complexes in aqueous electrolytes—I. Time-resolved EQCM study

Using a quartz supported silver electrode in potential step experiments, simultaneous measurements of current and electrode mass responses have shown that in parallel to electroreduction of silver cyanide complexes from water solutions the oxidation of electrolyte species occurs. In conjunction with the results of published studies an assumption is made that the adsorbed cyanide is the species which is oxidized.

The mechanism of electroreduction of silver cyanide complexes in aqueous electrolytes—II. Interpretation of SERS data

Time dependencies of the intensities and FWHM of the adsorbed cyanide Raman stretching band correlate with the features of the time dependencies of electron numbers obtained from EQCM measurements. Quantum-chemical ab initio calculations show that the excitation wavelength of about 765 nm excites electron transitions between the [Ag43CN−] states, whose quadrupole moments differ greatly. The earlier measured maxima in Raman excitation profiles for different adsorbates on roughened silver surface are in the following order (nm): ruthenium red ([Ru3O2(NH3)14]6+) ~ 590 < triphenylphosphine ~ 620 nm < pyridine ~ 720 < cyanide which coincides with the decrease in size of these molecules. The contribution due to the excitation in the Ag4+ cluster is larger when the adsorbate is smaller because of the more closely localized vibrational modes whereas contribution to the Raman scattering enhancement due to the excitation of surface plasma oscillations in the macroscopic silver clusters is constant.

Effect of anions on the underpotential deposition of thallium(I) on polycrystalline silver

Underpotential deposition (upd) of thallium(I) on a polycrystalline silver surface in solutions containing specifically adsorbing anions (sulphate and chloride) has been studied by voltammetry and the electrochemical quartz crystal microbalance (EQCM). The specific adsorption of thallium cations on the silver surface at potentials positive with respect to the pzc appears to be enhanced by the specific adsorption of anions. This leads to ion pair formation between the specifically adsorbed thallium cation and anion even at potentials positive with respect to the upd region. The decrease in the upd shift is explained by the fact that additional energy is required to break the bond between the formed pair. The electrode mass change measured by EQCM is smaller due to the discharge of thallium cations from the adsorbed ion pairs. The agreement between voltammetric and EQCM data is observed in the potential region close to the bulk thallium deposition where the adsorption of anions is weak and, consequently, there is little formation of ion pairs. The effect of sulphate and chloride anions on the thallium upd process is in accordance with their adsorbing strength. It seems very likely that this scheme can be applied when other upd processes in strongly adsorbing anions containing solutions are considered.

Mechanism of cadmium underpotential adsorption on platinum electrodes from acidic aqueous media: Part I. Analysis of potential step relaxation data at the initial stage of cadmium underpotential adsorption

Abstract A consideration of potential step relaxation data leads to the proposal of a mechanism for the underpotential adsorption of cadmium(II) on platinum electrodes in the more positive potential region. The mechanism involves the following: (1) direct underpotential adsorption of cadmium(II) from the solution onto sites of the first type followed by one-electron transfer; (2) rapid surface migration of cadmium(I) between two types of adsorption sites; (3) discharge of cadmium(I) adsorbed onto sites of the second type; (4) slow underpotential adsorption of cadmium(II) from the solution onto sites of the second type followed by simultaneous two-electron transfer. Surface and kinetic parameters were obtained for the unit steps in the above mechanism. Equilibrium constants for the surface equilibration between two adsorption states were determined via analysis of the transformed small potential step relaxation data in (real) Laplace space. In this analysis a method which takes the distribution of different adsorption sites on the surface into account is suggested.

Reduction in pressure drop for pipe flow due to applied electric potentials to the pipe

For all forms of transport of fluids in pipes, there is loss of pressure due to the friction. It has been shown that an electrical potential applied to the pipe wall can reduce water flow friction. Piezometric pressure loss over the 13.1 m slanting epoxy coated pipe made of steel, through which water was flowing, decreased when pipe was exposed to positive DC-potentials in the range 0.6–1.6 V. Maximum reduction was 2% with an applied potential of 1.0 V. Results from full scale experiments in a hydroelectric power plant (12.5 MW, 85 GWh) show that head loss decreased from 45.9 m to 39.8 m at maximum flow rate after 2.5 years of exposure to 1.1 V. Similar results for the head loss in another power plant (28 MW, 116 GWh) were 17.5 and 17.2 m, respectively, after 9 months of exposure to this DC-potential. The positive polarization of the pipes was noticeable throughout the whole length of the pipe.