Francisco Armijo

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 pHu20055.85, using sodium perchlorate as electrolyte, the polymer does not lose its activity for O2 reduction.

Catalytic Electrooxidation of 2-Mercaptoethanol on Perchlorinated Iron Phthalocyanine Adsorbed on a Graphite Electrode

In this article we show that iron perchlorinated phthalocyanine (FePcCl16), adsorbed on an OPG electrode, acts as a catalyst for the electrooxidation of 2-mercaptoethanol (R-SH), lowering the overpotential of the reaction by near 0.3 V, compared to the unmodified OPG. A Tafel slope close to 0.12 V/decade was observed, indicating that the first electron-transfer is rate determining. Chemical orders of one in R-SH and in OH− are obtained. The linearity of a plot of log I vs. log [RSH] indicates that this system could have potential applications in the amperometric detection of thiols.

Effect of the Substituents on the Ligand of Iron Phthalocyanines Adsorbed on Graphite Electrodes on Their Activity for the Electrooxidation of 2‐Mercaptoethanol

We have investigated the electrocatalytic activity of five iron phthalocyanines for the electrooxidation of 2-mercaptoethanol, with the complexes preadsorbed on a ordinary pyrolytic graphite electrode. The potential of Fe[II]/Fe[I] and Fe[III]/Fe[II] redox processes on the adsorbed phthalocyanines are shifted to more positive potentials by the effect of electron withdrawing groups −CO2−, −SO3− and −Cl and to more negative potentials by the electron-donating methoxy group compared to −H in unsubstituted FePc. The electrocatalytic activity, measured as current at constant potential, decreases as: Fe-octamethoxyphthalocyanine>Fe-phthalocyanine>Fe-tetracarboxyphthalocyanine>Fe-tetrasulfonatedphthalocyanine>Fe-perchlorinatedphthalocyanine. The most oxidant complex (Fe-perchlorinatedphthalocyanine) is the least active, which is contrary to what would be expected on thermodynamic grounds. This can be attributed to the fact that the reaction proceeds via an inner-sphere mechanism when the metal center is in state of oxidation II.

Electrocataltyic oxidation of hydrazine at polymeric iron-tetraaminophthalocyanine modified electrodes

Abstract Electrocatalytic hydrazine oxidation was studied by using a glassy carbon electrode coated with monomeric and polymeric Fe-tetraaminophthalocyanine. The polymeric complex-modified electrode is a better catalyst than the monomer-modified electrode. It presents higher activity at lower potentials and a very good reproducibility. A linear correlation between I p and hydrazine concentration in a wide range, from 1×10 −6 to 1×10 −2 xa0M at pH 13 for the polymer-modified electrode was obtained. The open circuit measurements for the polymer-modified electrode in aqueous solution in both presence and absence of hydrazine show that an electronic transfer occurs without an applied potential, from the hydrazine to the Fe (II) metal center. The kinetic electro-oxidation parameters for the polymer-modified electrode were investigated and a probable mechanism operating at pH 13 is proposed.

EVIDENCE OF A STABLE CHARGE-TRANSFER ADDUCT BETWEEN 2-MERCAPTOETHANOL AND COBALT-POLYTETRAAMINOPHTHALOCYANINE

Abstract The electro-oxidation of 2-mercaptoethanol by poly-Co-tetraaminophthalocyanine (p-Co-TAPc) and poly-metal-free-tetraaminophthalocyanine (p-H2TAPc), absorbed on electrode surfaces has been investigated by UV-visible spectroelectrochemistry and electrochemical techniques. In the case of p-CoTAPc, an irreversible oxidation wave is obtained by cyclic voitammetry, whereas p-H2PcTA practically does not show activity. The foot of the oxidation, as the open circuit potential measurements indicate that the responsible redox couple is Co(II)/Co(I). The p-CoTAPc modified-electrode loses its activity after a first potential cycle. UV-visible spectroelectrochemical measurements show a charge transfer band (metal to ligand) for the p-CoTAPc between Q and Soret bands when negative potentials are applied and Co(I) is obtained. The presence of 2-mercaptoethanol promotes the appearance of the charge transfer band at open circuit potential and retain this band even at potentials as positive as +0.2V where normally the Co center is in +2 oxidation state. The permanence of a stable charge transfer band indicates the formation of a stable charge-transfer adduct between Co(I) and the thiol. This adduct would be responsible for the loss of catalytic activity for p-CoTAPc after the first oxidation cycle.

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

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.

Electrocatalysis of NO2- on poly-M-tetraaminophenylporphyrines (M = Ni, Cu) modified electrodes assisted by visible light

Porphyrins and phthalocyanines of transition metals are good catalysts for many redox reactions [1-7]. In order to increase their catalytic activity it is often necessary to modify the macrocycle with donor or acceptor substituents making the species more reductive or oxidant depending on the analyte. However, this process is a one-way modification, because the molecule enhances or diminishes the electronic density of the metal by the substituent effect