Cecilia Vázquez - Academia.edu (original) (raw)

Papers by Cecilia Vázquez

Research paper thumbnail of Charge transport on vertically aligned ZnO nanorods with different aspect ratios

Research paper thumbnail of Effect of the electrolyte composition on the response of a TIO2|CDS-Based Photoanode

Electrochimica Acta, 2014

ABSTRACT Sulfide solutions are the most widely selected electrolyte for the photoelectrochemical ... more ABSTRACT Sulfide solutions are the most widely selected electrolyte for the photoelectrochemical characterization of metal chalcogenide (like CdS and CdSe) based solar cells because its good hole scavenging properties and improved stabilization of the semiconductor sensitizer. However, the photocurrent values of CdS sensitized TiO 2 photoanodes depend on the sodium sulfide analytical concentration and pH values in the electrolyte solution. In this report, we show that the mass transport of the sulfide hole scavenger is the main limiting process and if its concentration is lower than the HO − concentration there is a competition for adsorption sites onto TiO 2 surface, decreasing the photocurrent value. A careful optimization of these two variables it is necessary in order to attaining high overall photoelectrochemical cell efficiency.

Research paper thumbnail of Nucleation and growth of silver nanostructures onto HOPG electrodes in the presence of picolinic acid

Journal of Electroanalytical Chemistry, 2013

ABSTRACT Silver electrodeposition onto HOPG electrodes in the presence of picolinic acid (PA) has... more ABSTRACT Silver electrodeposition onto HOPG electrodes in the presence of picolinic acid (PA) has been studied by cyclic voltammetry and chronoamperometry. Changes in the nucleation and growth mechanisms, which are dependent on the PA concentration and solution pH, have been observed. Formation of complexes with Ag+ ions and adsorption of the additive molecules on both, the substrate and the growing silver crystallites can be correlated with the potential dependence of the kinetic parameters, N0 and A. The amount, distribution (random or localized on the defects sites) and size of the crystallites on the substrate are influenced by the composition of the solution (PA concentration and pH) when the control of the nucleation and growth processes is regulated by application of a double potential program.

Research paper thumbnail of Copper electrodeposition onto hydrogenated Si(111) surfaces: Influence of thiourea

Journal of Electroanalytical Chemistry, 2010

Research paper thumbnail of Monitoring of Silver Electrodeposition onto HOPG Electrodes in the Presence of Picolinic Acid by in Situ Surface-Enhanced Raman Spectra Measurements

The Journal of Physical Chemistry C, 2014

ABSTRACT In situ surface-enhanced Raman spectra (SERS) have been recorded during silver potentiod... more ABSTRACT In situ surface-enhanced Raman spectra (SERS) have been recorded during silver potentiodynamic electrodeposition onto HOPG electrodes from solutions containing silver perchlorate and picolinic acid (PA). Modification of the composition and pH of the electrolyte has allowed us to achieve an adequate control of the electroactive species distribution in solution. The adsorption behavior of different PA species on silver rowing crystallites has been studied by using the potential dependence of SERS signals. Analysis of the vibrational bands from additive molecules has allowed us to establish that at pH > 3.0 the PA anion is the most stable species on the electrode surface, whereas the predominant species in solution is the zwitterion. At pH 0.3, adsorption of zwitterion and anion species onto the silver surface, even though the PA cation is predominant in the solution, has been evidenced. For all the SERS spectra it was possible to infer the adsorption geometry and the ClO4− ion coadsorption. Detection of intensified signals of the adsorbed additive is facilitated by the morphological characteristics of the particles (globular flower-like structures), which results to be a good active SERS substrate on the HOPG electrodes. Spectroelectrochemical experiments are correlated with the SEM micrographs of the silver crystallites.

Research paper thumbnail of Spectroelectrochemical study of picolinic acid adsorption during silver electrodeposition

Electrochimica Acta, 2015

The adsorption of picolinic acid (PA) onto HOPG electrodes during silver electrodeposition at pH ... more The adsorption of picolinic acid (PA) onto HOPG electrodes during silver electrodeposition at pH 3.0 was examined using conventional electrochemical techniques: cyclic voltammetry and impedance measurements (differential capacity-potential plots) and Surface-Enhanced Raman Spectroscopy (SERS), through a wide range of electrode potentials. The spectroelectrochemical results indicate that the electroactive species for silver electrodeposition are Ag + ions and [Ag(Pic)] complexes, in spite of the predominant species in solution being the zwitterion (HPic). Adsorption of the anion (Pic À ) occurs through a wide potential range where the electrode surface charge density is positive. However, HPic deprotonation, hydrogen formation and Pic À desorption, with the consequent decrease in SERS intensity, occur at the zero-charge potential (pzc) for HOPG.

Research paper thumbnail of Charge transport on vertically aligned ZnO nanorods with different aspect ratios

Research paper thumbnail of Effect of the electrolyte composition on the response of a TIO2|CDS-Based Photoanode

Electrochimica Acta, 2014

ABSTRACT Sulfide solutions are the most widely selected electrolyte for the photoelectrochemical ... more ABSTRACT Sulfide solutions are the most widely selected electrolyte for the photoelectrochemical characterization of metal chalcogenide (like CdS and CdSe) based solar cells because its good hole scavenging properties and improved stabilization of the semiconductor sensitizer. However, the photocurrent values of CdS sensitized TiO 2 photoanodes depend on the sodium sulfide analytical concentration and pH values in the electrolyte solution. In this report, we show that the mass transport of the sulfide hole scavenger is the main limiting process and if its concentration is lower than the HO − concentration there is a competition for adsorption sites onto TiO 2 surface, decreasing the photocurrent value. A careful optimization of these two variables it is necessary in order to attaining high overall photoelectrochemical cell efficiency.

Research paper thumbnail of Nucleation and growth of silver nanostructures onto HOPG electrodes in the presence of picolinic acid

Journal of Electroanalytical Chemistry, 2013

ABSTRACT Silver electrodeposition onto HOPG electrodes in the presence of picolinic acid (PA) has... more ABSTRACT Silver electrodeposition onto HOPG electrodes in the presence of picolinic acid (PA) has been studied by cyclic voltammetry and chronoamperometry. Changes in the nucleation and growth mechanisms, which are dependent on the PA concentration and solution pH, have been observed. Formation of complexes with Ag+ ions and adsorption of the additive molecules on both, the substrate and the growing silver crystallites can be correlated with the potential dependence of the kinetic parameters, N0 and A. The amount, distribution (random or localized on the defects sites) and size of the crystallites on the substrate are influenced by the composition of the solution (PA concentration and pH) when the control of the nucleation and growth processes is regulated by application of a double potential program.

Research paper thumbnail of Copper electrodeposition onto hydrogenated Si(111) surfaces: Influence of thiourea

Journal of Electroanalytical Chemistry, 2010

Research paper thumbnail of Monitoring of Silver Electrodeposition onto HOPG Electrodes in the Presence of Picolinic Acid by in Situ Surface-Enhanced Raman Spectra Measurements

The Journal of Physical Chemistry C, 2014

ABSTRACT In situ surface-enhanced Raman spectra (SERS) have been recorded during silver potentiod... more ABSTRACT In situ surface-enhanced Raman spectra (SERS) have been recorded during silver potentiodynamic electrodeposition onto HOPG electrodes from solutions containing silver perchlorate and picolinic acid (PA). Modification of the composition and pH of the electrolyte has allowed us to achieve an adequate control of the electroactive species distribution in solution. The adsorption behavior of different PA species on silver rowing crystallites has been studied by using the potential dependence of SERS signals. Analysis of the vibrational bands from additive molecules has allowed us to establish that at pH > 3.0 the PA anion is the most stable species on the electrode surface, whereas the predominant species in solution is the zwitterion. At pH 0.3, adsorption of zwitterion and anion species onto the silver surface, even though the PA cation is predominant in the solution, has been evidenced. For all the SERS spectra it was possible to infer the adsorption geometry and the ClO4− ion coadsorption. Detection of intensified signals of the adsorbed additive is facilitated by the morphological characteristics of the particles (globular flower-like structures), which results to be a good active SERS substrate on the HOPG electrodes. Spectroelectrochemical experiments are correlated with the SEM micrographs of the silver crystallites.

Research paper thumbnail of Spectroelectrochemical study of picolinic acid adsorption during silver electrodeposition

Electrochimica Acta, 2015

The adsorption of picolinic acid (PA) onto HOPG electrodes during silver electrodeposition at pH ... more The adsorption of picolinic acid (PA) onto HOPG electrodes during silver electrodeposition at pH 3.0 was examined using conventional electrochemical techniques: cyclic voltammetry and impedance measurements (differential capacity-potential plots) and Surface-Enhanced Raman Spectroscopy (SERS), through a wide range of electrode potentials. The spectroelectrochemical results indicate that the electroactive species for silver electrodeposition are Ag + ions and [Ag(Pic)] complexes, in spite of the predominant species in solution being the zwitterion (HPic). Adsorption of the anion (Pic À ) occurs through a wide potential range where the electrode surface charge density is positive. However, HPic deprotonation, hydrogen formation and Pic À desorption, with the consequent decrease in SERS intensity, occur at the zero-charge potential (pzc) for HOPG.