Modulated reflectance spectroscopy and voltammetry of the sulphide/gold system

The electroadsorption of sulphide species on gold and the growth of sulphur multilayers have been investigated by optical and electrochemical techniques in sodium tetraborate buffer as the supporting electrolyte (pH 7.0 and 9.2) at 25°C. Differential reflectance spectra indicate that the adsorption of sulphide begins inside the hydrogen evolution reaction (HER) region. The HER is catalysed by the presence of sulphide species on the electrode. During the growth of sulphur multilayers, soluble polysulphide species can be optically detected either as intermediates under diffusion-controlled kinetics or as products of a chemical reaction between sulphide ions and the deposited sulphur layer. The steep fall in the integral reflectance at 0.4 V (vs. SHE) is interpreted through the incorporation of light-absorbing polysulphides into the structure of the deposited sulphur layer.Instituto de Investigaciones Fisicoquímicas Teóricas y AplicadasFacultad de Ciencias Exacta

Modulated reflectance spectroscopy and voltammetry of the sulphide/gold system

The electroadsorption of sulphide species on gold and the growth of sulphur multilayers have been investigated by optical and electrochemical techniques in sodium tetraborate buffer as the supporting electrolyte (pH 7.0 and 9.2) at 25°C. Differential reflectance spectra indicate that the adsorption of sulphide begins inside the hydrogen evolution reaction (HER) region. The HER is catalysed by the presence of sulphide species on the electrode. During the growth of sulphur multilayers, soluble polysulphide species can be optically detected either as intermediates under diffusion-controlled kinetics or as products of a chemical reaction between sulphide ions and the deposited sulphur layer. The steep fall in the integral reflectance at 0.4 V (vs. SHE) is interpreted through the incorporation of light-absorbing polysulphides into the structure of the deposited sulphur layer.Instituto de Investigaciones Fisicoquímicas Teóricas y AplicadasFacultad de Ciencias Exacta

Espectroelectroquímica de fotocatalizadores supramoleculares para reducción de co2

La reducción electrocatalítica de CO2 usando complejos de rutenio polipiridilo, Ruα y Ruβ, se estudió por voltamperometría en dimetilformamida DMF con 1M H2O. El primer proceso de reducción para Ruα y Ruβ en DMF: H2O muestra reversibilidad en su respuesta voltamétrica. Los potenciales redox de las ondas son -0.64 V (α) y -0.60 V (β) (vs Ag/AgCl). La corriente de la onda catódica para Ruα y Ruβ se incrementa con la adición de CO2 a la solución lo que indica reducción catalítica de CO2 en -0.60 V y -0.57 V respectivamente. La presencia de un sitio reactivo de nitrógeno en el ligando ptpb (4,5,9,11,14 -pentaaza-benzo(α o β)-trifenileno) facilita la formación de un intermediario tipo carbamato. Se describen reflectancias diferenciales, R/R vs. potencial en N2 y CO2, a 575 y 564 nm empleadas para seguir la formación de las especies radicales monoreducidas Ruα•- and Ruβ•-A combination of electro and spectroelectrochemistry have been used to study the electrocatalytic reduction of CO2 in the presence of ruthenium polypyridyl, Ru and Ruβ, complexes. Measurements were conducted in DMF:H2O. The first redox processes for Ruα and Ruβ show reversible voltammetric waves at -0.64 V and -0.60 V vs Ag/AgCl respectively. A clear increase in the cathodic wave of both Ruα and Ruβ occurs when CO2 is added to the solution pointing to a catalytic wave of the CO2 reduction at -0.60 V and -0.57 V respectively. The presence of a reactive nitrogen site on the ptpb (4,5,9,11,14 -pentaaza-benzo(α o β) -triphenylene) (either α or β) ligand facilitates the formation of a CO2 carbamate-type intermediate. Differential reflectance, R/R, vs. potential profiles in N2 and CO2 solutions show the consumption of the complex radical anion in the presence of CO2. R/R /potential curves are shown at 575 and 564 nm to track the electrochemical evolution of monoreduced Ruα •- and Ruβ •- radicals respectivelyFil: Franco Pachon, Yeimi Milena. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Tacconi, Norma. University Of Texas; Estados UnidosFil: MacDonnell, Frederick M.. University Of Texas; Estados UnidosFil: Lezna, Reynaldo Oscar. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentin

Optical and electrochemical study of the sulphide/silver system

The behaviour of sulphide species at a silver/electrolyte interface along with the electrodeposition of thin Ag2S films have been studied by a combination of electrochemical and in situ optical methods. The potential region between −1.08 and −0.470 V (nhe), pre-peak zone, is mainly characterized by a reversible process at −0.870 V, overlapping and catalysing the her, ascribed to the formation of an Ag−(Sh−ads bond. Phase Ag2S deposits were found to fit a linear relationship between reflectance, in the blue region, and charge. The oxidation of surface Ag2S (postwave) is readily observed by differential reflectance at potentials positive of the onset of bulk Ag2S formation. The rough silver surface brought about by the reduction of Ag2S allows a strong coupling between photons and surface plasmons.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Modulated reflectance spectroscopy and voltammetry of the sulphide/gold system

The electroadsorption of sulphide species on gold and the growth of sulphur multilayers have been investigated by optical and electrochemical techniques in sodium tetraborate buffer as the supporting electrolyte (pH 7.0 and 9.2) at 25°C. Differential reflectance spectra indicate that the adsorption of sulphide begins inside the hydrogen evolution reaction (HER) region. The HER is catalysed by the presence of sulphide species on the electrode. During the growth of sulphur multilayers, soluble polysulphide species can be optically detected either as intermediates under diffusion-controlled kinetics or as products of a chemical reaction between sulphide ions and the deposited sulphur layer. The steep fall in the integral reflectance at 0.4 V (vs. SHE) is interpreted through the incorporation of light-absorbing polysulphides into the structure of the deposited sulphur layer.Instituto de Investigaciones Fisicoquímicas Teóricas y AplicadasFacultad de Ciencias Exacta

Potentiodynamic characteristics of ruthenized platinum electrodes in sulphuric acid solutions

The potentiodynamic response of ruthenized platinum electrodes in 0.5 M and 12 M H2SO4 at 25°C is investigated. The E/I profiles depend on the electrode history and involve sintering-type effects. In 12 M H2SO4 they can be analysed in more detail because the separation of the H-adatom and O-electroadsorption potential ranges is greater than in 0.5 M H2SO4. Thus, four different stages related to the oxide layer are distinguished. The interpretation of the corresponding overall processes is given in terms of the equilibrium potentials of the Ru/H2O system and the reversibility characteristics of the different stages derived from the various potential/time perturbation programs are discussed through reaction patterns previously considered for these reactions on other noble metals.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Electromodulated infrared spectroscopy of methanol electrooxidation on electrodispersed platinum electrodes: Enhancement of reactive intermediates

EMIRS spectra of the surface species resulting from methanol electrosorption on electrodispersed Pt were obtained by working under a wide range of experimental conditions, i.e. electrode roughness factor, methanol concentration and mean modulation potential. The intensity of the absorption band related to linearly adsorbed CO-species, COL, at ca. 2030–2080 cm−1 decreases on increasing the electrode roughness factor, a fact which is interpreted as a decrease in the CO adsorbate poisoning effect on electrodispersed Pt surfaces. As a consequence, under well-defined conditions, several bands are observed which might be assigned to adsorbed intermediates and reactive species. EMIRS also reveals a competition between COB and COL at high surface coverages. Spectral data for methanol electrooxidation on electrodispersed electrodes correlate well with the expected structure of this type of electrode.Instituto de Investigaciones Fisicoquímicas Teóricas y AplicadasFacultad de Ciencias Exacta

Electromodulated infrared spectroscopy of methanol electrooxidation on electrodispersed platinum electrodes: Enhancement of reactive intermediates

EMIRS spectra of the surface species resulting from methanol electrosorption on electrodispersed Pt were obtained by working under a wide range of experimental conditions, i.e. electrode roughness factor, methanol concentration and mean modulation potential. The intensity of the absorption band related to linearly adsorbed CO-species, COL, at ca. 2030–2080 cm−1 decreases on increasing the electrode roughness factor, a fact which is interpreted as a decrease in the CO adsorbate poisoning effect on electrodispersed Pt surfaces. As a consequence, under well-defined conditions, several bands are observed which might be assigned to adsorbed intermediates and reactive species. EMIRS also reveals a competition between COB and COL at high surface coverages. Spectral data for methanol electrooxidation on electrodispersed electrodes correlate well with the expected structure of this type of electrode.Instituto de Investigaciones Fisicoquímicas Teóricas y AplicadasFacultad de Ciencias Exacta

Optical and electrochemical behaviour of the adsorption of potassium ethyl xanthate on gold

The first stages of the electroadsorption of ethyl xanthate (EX) on polycrystalline gold have been studied by optical and electrochemical techniques covering the 5 × 10−6 to 1 × 10−3 M concentration range. According to ac voltammetry and electroreflectance measurements, the adsorption of EX begins at −1.4 V (vs. SCE), in the HER potential region, followed by a capacitative process at −1.0 V. Both stages can be ascribed to the formation of different bonds between the EX and the gold surface through the sulphur atoms of the molecule. The following electroadsorption stage at −0.7 V implies the formation of a surface compound leading subsequently to layer growth. Differential reflectivity was particularly useful in providing information'on this type of complex adsorption process without appreciable interference from charging currents or stray faradaic reactions.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

In-situ spectroelectrochemistry of adsorbed methylene blue on a sulphur-modified gold electrode

The properties of a methylene blue layer adsorbed onto a sulphur-modified gold electrode have been studied by electrochemical and in-situ reflectance spectroscopy in the visible region. At saturation coverage, methylene blue monomer and dimer bands were observed in the double-layer region through the electrochromism of the adsorbed film arising from the effect of the double-layer field on the molecule transition moment. Possible dye orientations in the adsorbed state are discussed with the aid of the optical measurements. At low surface concentrations, the optical signal stems from modulation of the monomer/dimer interconversion. Repeated electrochemical reduction and oxidation of adsorbed methylene blue result in gradual desorption of the dimer species, probably due to a change in the molecular geometry upon reduction which may evolve from a planar configuration to a folded structure.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada