The Surface Potential of Water at Metal-Solution Interfaces

Relative values of the surface poitential of water at metal- aqueous solution interfaces at the potential of zero charge are derived by comparing experimental charge-potential curves for various metals. The principle of the method is presented and discussed. Absolute values for all the othe1r mefa~s are obtamed by estimating the absolute value of the surface potential of water on Hg. Three indeipendent routes are suggested. They are described and discussed. Experimental results are presented. The final estima: te sugigests that the surface potential of water on Hg is between 0.07 a1D.d 0.08 V, probably closer to 0.07 V. Water molecules are oriented wUh the oxy,gen atom facing the solid for all the metals investigated. A model is proposed to explaiin the metal-dep\u27endent orientation of water at the 1nterface with electrodes at the potential of ze1ro charge

Preparation and Characterization of Mixed-Oxide Electrocatalysts Based on RuO₂ and IrO₂

The formation processes of RuO2/TiO2, IrO2/TiO2 and IrO2/ZrO2 film electrodes have been studied by combined thermoanalytical and mass-spectrometric methods. The obtained materials have been characterized by cyclic voltammetry (CV). The precursor path leading to mixed oxides for the first two groups of matetials, consists of several stages, including solvent desorption, oxidative cracking, combustion, noble-metal chloride decomposition. Minima of the temperature of chlorine release and organic combustion have been observed for precursor salt mixtures with intermediate-low noble-metal concentrations. The microstructural investigation, carried out by wide-angle X-ray scattering (WAXS) has shown that solid solutions are formed within quite wide composition ranges for TiO2-stabilized materials. For the IrO2/ZrO2 system, segregation of amorphous ZrO2 takes place for IrO2 concentrations ≤ 80 mol-%. For the TiO2-stabilized samples, the characterization by cyclic voltammetry has shown that maxima of charge-storage capacity are observed for those electrodes whose composition is in the range of minimum temperature for the precursor reaction. A dependence of the faradaic voltammetric charge on the carbon content of the electrode films, as determined by nuclear reaction analysis (NRA), has been shown. The experimental results have been explained hypothesizing that minima of pyrolysis temperature involve less favorable conditions for rearrangements in the reacting films, and, consequently, larger degree of defectivity. In the case of IrO2/ZrO2 electrodes, the segregation of the amorphous ZrO2 phase seems to be main reason for the maximum of charge-storage capacity observed at 80 mol-% of IrO2

Electrochemical disinfection of groundwater for civil use – An example of an effective endogenous advanced oxidation process

Lab-scale experiments using real groundwater were carried out using the CabECO® reactor system in order to evaluate its suitability for producing safe water, acceptable for civil purposes. Trials were carried out in discontinuous and in continuous mode, analyzing the influence of electrical and hydraulic process parameters on the quality of treated water. The use of highly boron-doped diamond electrodes in the reactor allowed the electrosynthesis of considerable amounts of ozone. Because of the relatively high amount of chloride in the groundwater samples, a mixture of HOCl/ClO- was also synthesized. Somewhat unexpectedly, the increase in the current density in the explored range 100 -1000 A m-2 was accompanied by an increase in the faradaic yield of the electrosynthesis of oxidants, which was more pronounced for ozone than for free chlorine. As reported in literature, the main radical intermediate in the relevant reactions is ●OH, which can lead to different oxidation products, namely ozone and HOCl/ClO-. The electrolytic treatment also caused a decrease in the concentration of minor components, including NH4+ and Br-. Other byproducts were ClO3- and ClO4-, although their concentration levels were low. Moreover, due to alkali formation at the cathode surface, the precipitation of calcium and magnesium carbonates was also observed. In addition, the experimental investigation showed that even Pseudomonas aeruginosa and Legionella could be completely removed in the treated stream, due to the unique capacity of the reactor to synthesize biocidal agents like ozone, HOCl/ClO-, and chloramines. These effects were particularly evident during batch experiments.Lab-scale experiments using real groundwater were carried out using the CabECO® reactor system in order to evaluate its suitability for producing safe water, acceptable for civil purposes. Trials were carried out in discontinuous and in continuous mode, analyzing the influence of electrical and hydraulic process parameters on the quality of treated water. The use of highly boron-doped diamond electrodes in the reactor allowed the electrosynthesis of considerable amounts of ozone. Because of the relatively high amount of chloride in the groundwater samples, a mixture of HOCl/ClO− was also synthesized. Somewhat unexpectedly, the increase in the current density in the explored range 100–1000 A m−2 was accompanied by an increase in the faradaic yield of the electrosynthesis of oxidants, which was more pronounced for ozone than for free chlorine. As reported in literature, the main radical intermediate in the relevant reactions is [rad]OH, which can lead to different oxidation products, namely ozone and HOCl/ClO−. The electrolytic treatment also caused a decrease in the concentration of minor components, including NH4+ and Br−. Other byproducts were ClO3− and ClO4−, although their concentration levels were low. Moreover, due to alkali formation at the cathode surface, the precipitation of calcium and magnesium carbonates was also observed. In addition, the experimental investigation showed that even Pseudomonas aeruginosa and Legionella could be completely removed in the treated stream, due to the unique capacity of the reactor to synthesize biocidal agents like ozone, HOCl/ClO−, and chloramines. These effects were particularly evident during batch experiments

Electrochemical oxidation of oxalic acid in the presence of halides at boron doped diamond electrode

Aim of this work is to discuss the electrochemical oxidation of oxalic acid (OA), analyzing the influence of NaCl and NaBr. Experiments were carried out at boron-doped diamond (BDD) electrodes, in alkaline media. BDD electrodes have a poor superficial adsorptivity so their great stability toward oxidation allows the reaction to take place with reactants and intermediates in a non-adsorbed state. The process is significantly accelerated by the presence of a halogen salt in solution; interestingly, the mediated process does not depend on applied current density. Based on the results, bromide was selected as a suitable mediator during OA oxidation at BDD. Br- primarily acts in the volume of the solution, with the formation of strong oxidants; while Cl- action has shown lower improvements in the OA oxidation rate at BDD respect to the results reported using Pt electrode. Finally, the parameters of removal efficiency and energy consumption for the electrochemical incineration of OA were calculated. O objetivo deste trabalho é discutir a oxidação eletroquímica do ácido oxálico (AO), analisando a influência do NaCl e NaBr. Experimentos foram realizados em eletrodos de diamante dopados com boro (DDB), em meio alcalino. Eletrodos DDB têm uma baixa adsortividade superficial, portanto sua grande estabilidade frente à oxidação permite que a reação ocorra com reagentes e intermediários não adsorvidos. O processo é significativamente acelerado pela presença de sal de halogênio na solução; curiosamente, o processo mediado não depende da densidade de corrente aplicada. Com base nos resultados, o brometo foi selecionado como um mediador apropriado durante a oxidação de AO em DDB. Br- age primeiramente no volume da solução, com a formação de oxidantes fortes, enquanto a ação do Cl- mostrou melhoras mais baixas na oxidação do AO em BDD, com relação aos resultados relatados usando eletrodo de Pt. Finalmente, os parâmetros de eficiência de remoção e consumo de energia para a incineração eletroquímica de AO foram calculados

Heterogeneous catalysis in internal combustion engines

none2Catalytically active materials having suitable thermal stability and catalytic activity are localized on internal-wall surfaces of a combustion chamber. The catalytic activity is performed during the combustion reaction for the enhancement of combustion reactions and redn. of pollutants emissions.noneFERRO SERGIO; DE BATTISTI A.Ferro, Sergio; DE BATTISTI, Achill

Electron transfer reactions at conductive diamond electrode

The electrochemical behavior of the iron(III)/iron(II) and the ferri/ferro–cyanide redox couples in aqueous media has been investigated at conductive diamond, to obtain information on the properties of this electrode material. The investigation has been carried out at as prepared and oxidized diamond surfaces, under conditions of different concentration and temperature. The electron transfer kinetics has been followed by cyclic voltammetry, quasi-steady polarization (low-field conditions) and AC impedance, and the results have been interpreted on the basis of the Hush model, attempting its extension to the ferri/ferro–cyanide redox couple as well

The electrical double layer between mercury and aqueous NaBF

Potentials of the sodium amalgam electrode have been determined with respect to a saturated calomel electrode at various concentrations of NaBF4 in the range 0.01 m to 1 m. γ± values have been evaluated by assuming that (i) the liquid junction potential EL changes trivially in the whole concentration range and (ii) the single ion activity strictly derivable from the experimental arrangement coincides with the mean ionic activity. Possible deviations of γ± from the thermodynamic value due to factors (i) and (ii) have been examined in detail and reliable estimations of the limits of accuracy have been made. As a conclusion, γ±'s as derived in this work have been estimated to be some 5 to 10 % higher than the true values at the highest concentrations, the deviation approaching rapidly negligible levels as the concentration is decreased. As a result, the γ±'s given in this Paper may be used with confidence for practical purposes, e.g in the graphical differentiation of the electrocapillary equation in the study of BF4- adsorption