Galo Ramírez

Electroreduction of Molecular Oxygen on Poly‐Iron‐Tetraaminophthalocyanine Modified Electrodes

In this work we have investigated the electrocatalytic activity for O2 reduction of monomeric (FePcTA) and polymeric (poly-FePcTA) iron tetraaaminophthalocyanine, deposited on glassy carbon. The activity of the electropolymerized ligand (poly-H2PcTA) was also investigated. Its activity is much lower than the activity of both monomeric and polymeric FePcTA. The electropolymerized FePcTA is more active and stable for O2 reduction than the monomeric species. In contrast to other Fe-phthalocyanines, poly-FePcTA only catalyzes the two-electron reduction of O2 to peroxide. Both monomeric and polymeric Fe species seem to form an adduct with oxygen and this causes a gradual deactivation, However at pH 5.85, using sodium perchlorate as electrolyte, the polymer does not lose its activity for O2 reduction.

A Supramolecular Cobalt–Porphyrin-modified Electrode, toward the Electroreduction of Co2

The electro-reduction of carbon dioxide was studied by using a glassy carbon electrode modified with Co(II)-tetrabenzoporphyrin as adsorbed layers or as a supramolecular system. In order to obtain the supramolecular electrode, 4-aminopyridine was chemically bonded to the electrodic surface. On this surface, a first layer of porphyrins was anchored by the pyridine as a fifth ligand. Packed on the first layer of porphyrins, a supramolecular system is formed. The electrode modified with physically adsorbed layers of porphyrins does not show catalytic response toward the electroreduction of CO2. However, the supramolecular electrode is very stable and shows a high catalytic response.

EFFECT OF THE CONDITIONS OF ELECTROPOLYMERIZATION ON THE ELECTROCATALYTIC RESPONSE OF NON-METALLED- POLY-TETRAAMINOPHTHALOCYANINE-MODIFIED ELECTRODES TOWARD THE REDUCTION OF OXYGEN

En este trabajo se realizo la electropolimerizacion por barrido continuo de potencial, de tetraaminoftalocianina sobre electrodos de carbon vitreo. Para esto, se utilizaron dos solventes, dimetilformamida y dimetilsulfoxido. En el caso del dimetilsulfoxido, se observa que a medida que transcurre la electropolimerizacion, empieza a ocurrir un proceso de sobre-oxidacion que finalmente destruye al polimero, modificando e inhibiendo sus propiedades electrocataliticas en la reduccion de oxigeno, comparado con el polimero preparado en dimetilformamida. Para evitar esta sobre-oxidacion, pueden utilizarse dos caminos: acortar el limite positivo de barrido de potencial, o bien, realizar la electropolimerizacion con un menor numero de ciclos. En el primer caso, se logra evitar la destruccion parcial del polimero obteniendose un electrodo de caracteristicas electrocataliticas similares al crecido en dimetilformamida. En el segundo caso, se obtiene un polimero que presenta una nueva senal redox y que es el de mayor electroactividad hacia la reduccion de oxigeno

Iron porphyrin-modified electrodes: influence of the method of modification on the stability and electroactivity in oxidation of sulfite or hydrogensulfite in ethanol–water solutions

The aim of this work is to study four types of modification of a glassy carbon electrode by Fe(III)-tetrakis(p-tetraaminophenyl)porphyrin and determine the influence of the method of immobilization of the complex on glassy carbon in electrocatalytic properties for the sulfite and hydrogensulfite oxidation in ethanol–water. The first modification was deposition of a drop of solution containing the porphyrin on a glassy carbon electrode and evaporation of the solvent (dry-drop method). The second method was immersion of the electrode at 54°C in a solution of dimethylformamide containing the porphyrin for 2 h. The third method consisted of the same heating treatment but after formation of a chemical bond of 4-aminopyridine on the glassy carbon surface, which acts as an axial ligand for the first layer of porphyrin. The fourth method involves electropolymerization of the porphyrin on the electrode surface. Important differences in stability, the potential where the oxidation wave begins and selectivity of the electrode to sulfite or hydrogensulfite were observed. The behavior of the polymer-modified electrode is different in water compared to ethanol–water.

SPECTROELECTROCHEMICAL STUDIES ON ITO MODIFIED ELECTRODES WITH A CONDUCTING COBALT (II) MACROCYCLE FILM IN THE ELECTROCHEMICAL REDUCTION OF CO2

The spectroelectrochemical properties of a conducting polymer derived from Co(II) tetra-3-amino-phenyl-porphyrin,(poly-Co(II)-TAPP) were studied towards the electrochemical reduction of CO2 on ITO surface. Under inert atmosphere, the results show that the polymer present a stable Co(I) oxidation state only in basic pH while in more acidic solution this Co(I) does not stabilize. Under CO2 atmosphere the reduced polymer forms a stable adduct with no clear electronic localization. The formation and the stability of this adduct could explain the wide distribution of reaction products

A potentiometric hydrazine sensor: para-Ni-tetraaminophenylporphyrin/Co-cobaltite/SNO2:F modified electrode

Three glass electrodes covered with Co-cobaltite/SnO2:F (to obtain conducting glass electrodes) modified with p-Ni-tetraaminophenylporphyrin are described. In one electrode the porphyrin was absorbed on the electrode surface at room temperature, in another the porphyrin was electropolymerized on the electrode surface by cyclic voltammetry, and in the third the bare electrode was immersed in DMF containing the porphyrin and refluxed 6 h at 150°C. The three electrodes were tested as electrocatalysts for the oxidation of hydrazine and as potentiometric sensors of this chemical. The electrode modified by refluxing showed good electrocatalytic behavior as well as a linear relationship between its open circuit potential and the concentration of hydrazine in a concentration range from 0.16 to 12 µM, with fast response. These characteristics indicate that the conducting glass electrode of Co-cobaltite/SnO2:F covered with p-Ni-tetraaminophenylporphyrin by the reflux method is a good potentiometric sensor of hydrazine. The active site is probably the ligand that changes its electron density by formation of a supramolecular system.

PARA-Ni-TETRAAMINOPHENYLPORPHYRIN/Co-COBALTITE/SnO2:F MODIFIED ELECTRODES: ELECTROCATALYTIC BEHAVIOR TOWARD THE OXIDATION OF HIDRAZINE

The aim of this work was the study of three different modified electrodes where the substrate and the porphyrin used to modify the electrodic surface was the same. The surface electrode was a glass covered by a layer of SnO2 doped with fluor. On this layer was formed a cubic spinel of Co-cobaltite. On this modified electrode was deposited or polymerized para-tetraaminophenylporphyrin of Ni (II). In each case, the treatment of the deposition of the porphyrin was different and the electrocatalytic behavior of the modified electrodes toward the oxidation of hydrazine drastically changes. In the case of a simple physically adsorbed layer of porphyrin, practically no electrocatalytic activity was found. In the case of a porphyrin deposited by reflux and cycled in basic solution, there is an important electrocatalytic activity giving N2 as product. This electrode was proved as an amperometric sensor of hydrazine and a very good linear relationship between current and concentration was determinate. Also, the polymeric electrode showed an important catalytic behavior toward the oxidation of hydrazine

CHEMICAL METALLATION OF POLY-P-TETRAAMINOPHENYLPORPHYRIN FILMS GROWN BY CYCLIC VOLTAMMETRY ON CONDUCTING GLASS ELECTRODES

In this paper we present a simple and mild procedure to incorporate cations of transition metals to a polymer of the free-ligand para-tetraaminophenylporphyrin (H2TAPP) in order to obtain similar responses as in the case of the direct electropolymerization of a metallic complex. Sometimes, it is not possible to obtain an electropolymerized complex under a determined set of conditions. Changes in the conditions of synthesis drastically alter the properties of the polymers and, thus, the modification of the parameters of synthesis is not a feasible method to obtain a desired polymer. In those cases, a polymer of the free-ligand can be obtained and then the metallic ions can be incorporated so that an identical polymer to the one that could be obtained from the direct polymerization of the complex is obtained.