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The present contribution describes an electrochemical system for the detection of alkaline phosphatase (ALP) enzyme inhibitors in seawater medium. Fluorescence spectroscopy and thermal unfolding results suggest that the state of free ALP is affected in this medium, yet the protein remains active. The enzyme activity can be evaluated using hydroquinone diphosphate as the substrate, with hydroquinone as the electrochemically monitored product. It has been demonstrated that encapsulation in conventional and organic modified silica matrices maintains ALP integrity, although diffusion across the formed monoliths hinders the electrochemical response. ALP@Phenyl-modified silica exhibits the best performance due to higher affinity between substrate molecules and aromatic moieties and, probably, to larger pore size. This electrochemical system can detect and quantify calyculin A in seawater at sub-nanomolar concentrations and it can also be employed for the development of electrochemical biosensors tailored for the marine environment.

Controlling direct electron transfer (DET) to redox proteins is of great interest for fundamental studies on biochemical processes and the development of biotechnological devices, such as biosensors or enzymatic fuel cells. Cytochrome c is a classical model protein for studying DET reactions that plays a key role in the onset of cellular apoptosis and the mitochondrial respiratory chain. In this contribution, we explored DET between cyt c and conducting polymers bearing the chemical structure of thiophene, specifically PEDOT, and its OH-containing derivative, PHMeEDOT. The combination of electrochemistry and in situ FTIR spectroscopy allowed us to gain more insight into the inner mechanism of DET at physiological pH. Hydrophilic interactions favour the correct orientation of the heme crevice of cytochrome c towards the polymer surface. When a positive charge is injected into the conducting polymer, the increasing electrostatic repulsion between protein and surface induces the desorption of lysine residues near the heme group and stimulates protein flipping. This effect was more pronounced at PEDOT- than PHMeEDOT-modified electrodes since the latter shows stronger interactions with lysine residues, partially hindering protein rotation at moderate potential. The potential-induced reorientation process was similar on both polymer surfaces, only at high positive potentials.

The development of non-expensive and efficient technologies for the elimination of Glyphosate (GLP) in water is of great interest for society today. Here we explore novel electrocatalytic effects to boost the anodic oxidation of GLP on Pt-doped (3-13met%) SnO2–Sb electrodes. The study reveals the formation of well disperse Pt nanophases in SnO2–Sb that electrocatalyze GLP elimination. Cyclic voltammetry and in-situ spectroelectrochemical FTIR analysis evidence carboxylate-mediated Pt-GLP electrocatalytic interactions to promote oxidation and mineralization of this herbicide. Interestingly, under electrolytic conditions Pt effects are proposed to synergistically cooperate with hydroxyl radicals in GLP oxidation. Furthermore, the formation of by-products has been followed by different techniques, and the studied electrodes are compared to commercial Si/BDD and Ti/Pt anodes and tested for a real GLP commercial product. Results show that, although BDD is the most effective anode, the SnO2–Sb electrode with a 13 met% Pt can mineralize GLP with lower energy consumption.

LaNi1-xCoxO3 perovskite materials were synthesized by a sol-gel method for use in electrochemical reactions which involve molecular oxygen. The metal oxides were characterized by different physicochemical techniques and it was observed that the incorporation of Co induces some changes in the surface of the materials that affect the electrocatalytic activity. The different perovskite metal oxides were mixed with carbon black (Vulcan) to improve their electrocatalytic performance. The results from TPR and TPD techniques supported the XPS interpretation suggesting that a stronger interaction between carbon material and metal oxides can be obtained by physically mixing the two materials. This interaction improves the electron transfer and enhances the catalytic activity. Among the as-prepared materials, it was observed that the electrocatalytic performance of LaNi1-xCoxO3 perovskite/Vulcan materials is higher than that of LaNiO3/Vulcan for ORR, but similar towards OER. It is claimed that Co3+ is more catalytic for ORR, while Ni3+ favors the OER. Moreover, the presence of Co stimulates the formation of chemisorbed oxygen species, which also favor the electron transfer. Metal oxides containing both cations show higher stability, being this effect more notorious for OER. LaNi0.5Co0.5O3/Vulcan seems a suitable bifunctional catalyst for both electrochemical reactions.

Manganese-based materials can catalyze the oxygen reduction reaction (ORR), although their activity is known to depend on the crystalline phases and on the concentration of surface-active species. In the present study, we have optimized these two parameters to obtain improved catalysts for ORR. A sol-gel method was used to synthesize LaMnO3-manganese oxides composites with different lanthanum-to-manganese atomic ratios. The synthesized materials, which can be described as La1-xMnOz, were tested under ORR conditions and characterized by several physicochemical techniques such as SEM, XPS, EDX or XRD. It was found that the concentration of lanthanum governs the formation of different crystal phases and determines the crystallite size. Besides, high values of x tend to increase the surface concentration of manganese and therefore to produce more active sites for ORR. Among the materials analysed, La0.6MnOz mixed with carbon black (Vulcan) showed the best electrocatalytic performance. The high tolerance to methanol makes this electrocatalyst a promising alternative to substitute Pt-based materials in alkaline electrolytes.

Transition metal oxide-based materials are an interesting alternative to substitute noble-metal based catalyst in energy conversion devices designed for oxygen reduction (ORR), oxygen evolution (OER) and hydrogen evolution reactions (HER). Perovskite (ABO3) and spinel (AB2O4) oxides stand out against other structures due to the possibility of tailoring their chemical composition and, consequently, their properties. Particularly, the electrocatalytic performance of these materials depends on features such as chemical composition, crystal structure, nanostructure, cation substitution level, eg orbital filling or oxygen vacancies. However, they suffer from low electrical conductivity and surface area, which affects the catalytic response. To mitigate these drawbacks, they have been combined with carbon materials (e.g. carbon black, carbon nanotubes, activated carbon, and graphene) that positively influence the overall catalytic activity. This review provides an overview on tunable perovskites (mainly lanthanum-based) and spinels featuring 3d metal cations such as Mn, Fe, Co, Ni and Cu on octahedral sites, which are known to be active for the electrochemical energy conversion.

[ES] El presente trabajo final de carrera se centra en el análisis del sistema eléctrico de potencia de la Isla de El Hierro y en el estudio de las tecnologías maduras de los sistemas estacionarios de pilas de combustible, para la generación de energía eléctrica por medio del hidrógeno. El análisis de la red eléctrica de la Isla permitirá: conocer su comportamiento, entender las fluctuaciones de la red originadas por la inconstancia de las energías renovables y cuantificar de forma aproximada la energía en forma de hidrógeno necesaria. A lo largo del TFG se plantean los siguientes desafíos, ¿Qué pasaría a día de hoy, si se sustituyese el diésel por hidrógeno? y ¿Qué le hace falta a la tecnología del hidrógeno para ser mínimamente competitiva con el diésel? La propuesta solución eliminará las emisiones de gases de efecto invernadero en la generación de energía, mejorará la calidad de la energía eléctrica y permitirá la integración del hidrógeno en otros sectores., [EN] This Degree Final Project focuses on the analysis of the electrical power system of the Island of El Hierro and the study of mature technologies of stationary fuel cell systems for the generation of electrical energy by means of hydrogen. The analysis of the island's electrical network will allow: knowing its behavior, understanding the fluctuations in the network caused by the inconstancy of renewable energies and approximately quantifying the necessary energy in the form of hydrogen. Throughout the TFG the following challenges are exposed: What would happen today, if diesel were replaced by hydrogen? And what does hydrogen technology need to be minimally competitive with diesel? The proposed solution will eliminate greenhouse gas emissions in power generation, improve the quality of electrical energy and allow the integration of hydrogen in other sectors.

The redox transitions of PANI in acidic medium have been monitored by a combination of cyclic voltammetry, in situ conductance and in situ FTIR spectroscopy. The results of the semiquantitative analysis strongly suggest that the classical tetrameric model of PANI does not satisfactorily describe the actual structures of the polymer at different redox states. An octameric model is revisited, with the inclusion of essential resonant structures, to provide an appropriate prediction of the relative IR intensity changes of the aromatic C-C stretching (at around 1520 cm-1) and the quinoid C=C stretching (at around 1590 cm-1) vibrations observed by FTIR, which are difficult to interpret by considering only 4 aniline rings. Particularly, it is found that the emeraldine state is better described as a resonance hybrid of the classical bipolaronic and semiquinoid (polaron lattice) structures, while most of the charge transferred at the onset of the second voltammetric peak comes from the additional oxidation of this hybrid, which becomes unstable in the electrochemical environment producing mineralization to CO2 and release of soluble quinones.

The understanding of exciton dynamics is a central issue in the operation of conjugated polymer-based optoelectronic devices, like solar cells, light-emitting diodes or electrochemiluminescent cells. In this work, we explore the applicability of combined in situ electrochemical fluorescence and UV-vis spectroscopies for the study of electrochemically induced quenching of photoluminescence as novel tools for the determination of exciton diffusion in a model conjugated polymer, poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylvynilene] (MEH-PPV). It is demonstrated that the quenching process observed upon electrochemical doping follows a linear Stern-Volmer mechanism at low doping levels, with a time-independent rate constant typical of diffusion-controlled annihilation processes. From the Stern-Volmer rate constant and the exciton-polaron critical distance, an exciton diffusion coefficient is derived whose value is in close agreement with those reported in the literature. These results support the suitability of these spectroelectrochemical techniques as fast and powerful alternative tools for the reliable determination of exciton diffusion coefficients in conjugated polymers.

En la presente Tesis Doctoral se centra en la síntesis de óxidos con estructura perovskita y espinela para las reacciones electroquímicas de reducción de oxígeno (ORR), evolución de oxígeno (OER) y evolución de hidrógeno (HER). Debido a que los óxidos metálicos poseen una baja conductividad eléctrica y baja área superficial que limitan sus aplicaciones catalíticas se mezclan con materiales de carbón para mitigar estas dos desventajas. Además, los materiales de carbón juegan un papel fundamental en las reacciones catalíticas favoreciéndolas debido a un efecto sinérgico con los óxidos metálicos. Los óxidos tipo perovskita LaB1-xB'xO3 (donde B es Mn o Ni y B' es Co) se sintetizaron a través de un método sol-gel. Tal como se puede observar en la formulación en este tipo de perovskitas se realiza una sustitución parcial del catión B con otro metal de transición 3d con el fin de modificar las propiedades fisicoquímicas y de este modo mejorar la actividad catalítica. Los materiales obtenidos presentan una buena actividad catalítica tanto en la ORR como en la OER. Del conjunto de materiales obtenidos se ha observado que los materiales. LaMn1-xCoxO3/ Vulcan presentan una buena actividad catalítica en la ORR, mientras que los materiales LaNi1-xCoxO3/ Vulcan tienen un mejor comportamiento en la OER. Además los materiales presentan una buena estabilidad y en el caso de la ORR una buena tolerancia al metanol. Además, con el fin de incrementar el número de sitios catalíticos en superficie se ha modificado la relación atómica de lantano y manganeso durante la síntesis y se ha obtenido materiales con una buena actividad catalítica debido al aumento de sitios catalíticos de Mn en la superficie debido a la formación de nuevas fases cristalinas catalíticamente activas. Los óxidos con estructura tipo espinela CuFe2O4 se han sintetizado mediante un método solvotermal con el fin de obtener nanopartículas para la ORR. Además, con el fin de mejorar las propiedades físicas, el óxido posteri

LaMn1−xCoxO3 perovskites were synthesized by a modified sol-gel method which incorporates EDTA. These materials’ electrochemical activity towards both oxygen reduction (ORR) and oxygen evolution reactions (OER) was studied. The cobalt substitution level determines some physicochemical properties and, particularly, the surface concentration of Co and Mn’s different oxidation states. As a result, the electroactivity of perovskite materials can be tuned using their composition. The presence of cobalt at low concentration influences the catalytic activity positively, and better bifunctionality is attained. As in other perovskites, their low electrical conductivity limits their applicability in electrochemical devices. It was found that the electrochemical performance improved significantly by physically mixing with a mortar the active materials with two different carbon black materials. The existence of a synergistic effect between the electroactive component and the carbon material was interpreted in light of the strong carbon–oxygen–metal interaction. Some mixed samples are promising electrocatalysts towards both ORR and OER.

In this study, the phosphonation of a polyaniline (PANI) backbone was achieved in an acid medium by electrochemical methods using aminophenylphosphonic (APPA) monomers. This was done through the electrochemical copolymerization of aniline with either 2- or 4-aminophenylphosphonic acid. Stable, electroactive polymers were obtained after the oxidation of the monomers up to 1.35 V (reversible hydrogen electrode, RHE). X-ray photoelectron spectroscopy (XPS) results revealed that the position of the phosphonic group in the aromatic ring of the monomer affected the amount of phosphorus incorporated into the copolymer. In addition, the redox transitions of the copolymers were examined by in situ Fourier-transform infrared (FTIR) spectroscopy, and it was concluded that their electroactive structures were analogous to those of PANI. From the APPA monomers it was possible to synthesize, in a controlled manner, polymeric materials with significant amounts of phosphorus in their structure through copolymerization with PANI.

A set of fluoro-functionalized polyaniline conducting polymers was synthesized by cyclic scanning of the potential from acidic solutions containing aniline and 2-fluoroaniline monomers. The monomer feed ratio was varied to modulate the composition of the synthesized materials. The fluorination level of the copolymers was quantified from X-ray photoelectron spectroscopy. The upper inversion potential of the cyclic scans was proved as a suitable tool to tune the fluorination level, as the reactivity of the growing chains depends strongly on that experimental parameter. We found that terminal fluorinated anilines present a reactivity for homocoupling 5 times lower than for heterocoupling, independently of the limiting potential. Conversely, aniline terminal groups present a reactivity strongly dependent on the limiting potential, favoring the heterocoupling reactions at high inversion potentials. The maximum fluorination level of polyaniline rings achieved is about 75%.

The chemical composition of a LaMnO3 perovskite was modified sequentially by an improved sol–gel method to include cobalt centers in some B sites formerly occupied by Mn. In this way, a representative set of materials of general formula LaMn1-xCoxO3 was obtained whose composition extends from LaMnO3 to LaCoO3. These perovskites, as promising materials for oxygen reduction or oxygen evolution reactions, were characterized by several imaging (SEM), spectroscopic (XPS, EDX) and diffraction (XRD) techniques to elucidate their structure and to demonstrate the existence of composition differences between the catalytic surface and the bulk material. Specifically, it was found that lanthanum ions prevail at the surface of the catalyst but high cobalt-substitution levels stimulate the surface enrichment in B cations in their respective higher oxidation states (Mn4+ and Co3+ against Mn3+ and Co2+). This phenomenon opens the possibility of tuning their electrocatalytic properties and to synthesize suitable materials for electrochemical reactions involving molecular oxygen.

The development of electrocatalysts based on the doping of copper over cobalt spinel supported on a microporous activated carbon has been studied. Both copper–cobalt and cobalt spinel nanoparticles were synthesized using a silica-template method. Hybrid materials consisting of an activated carbon (AC), cobalt oxide (Co3O4), and copper-doped cobalt oxide (CuCo2O4) nanoparticles, were obtained by dry mixing technique and evaluated as electrocatalysts in alkaline media for hydrogen evolution reaction. Physical mixtures containing 5, 10, and 20 wt.% of Co3O4 or CuCo2O4 with a highly microporous activated carbon were prepared and characterized by XRD, TEM, XPS, physical adsorption of gases, and electrochemical techniques. The electrochemical tests revealed that the electrodes containing copper as the dopant cation result in a lower overpotential and higher current density for the hydrogen evolution reaction.

Dopamine, norepinephrine, and epinephrine neurotransmitters can be detected by electrochemical oxidation in conventional electrodes. However, their similar chemical structure and electrochemical behavior makes a difficult selective analysis. In the present work, glassy carbon electrodes have been modified with silica layers, which were prepared by electroassisted deposition of sol–gel precursors. These layers were morphologically and compositionally characterized using different techniques, such as field emission scanning electron microscopy (FESEM), TEM, FTIR, or thermogravimetric analysis–mass spectrometry (TG-MS). The affinity of silica for neurotransmitters was evaluated, exclusively, by means of electrochemical methods. It was demonstrated that silica adsorbs dopamine, norepinephrine, and epinephrine, showing different interaction with silica pores. The adsorption process is dominated by a hydrogen bond between silanol groups located at the silica surface and the amine groups of neurotransmitters. Because of the different interaction with neurotransmitters, electrodes modified with silica films could be used in electrochemical sensors for the selective detection of such molecules.

Poly(3,4-ethylenedioxythiophene) doped with poly-(styrenesulfonate), PEDOT–PSS, films synthesized by electrochemical methods can be considered as poor electrocatalyst for the oxidation of ferrocene in aqueous solution. The rate of electron transfer to that redox probe decays progressively as the amount of deposited polymer increases and the true electroactive area available for the electrochemical reaction shows quite modest figures. We present here an alternative, simple way to enhance the properties of this material which uses, exclusively, electrochemical synthesis methods. The electrocatalytic performance can be significantly improved by inserting the polymer within a pre-deposited, three-dimensional porous silica matrix forming an interpenetrating hybrid material. On the one hand, the modified PEDOT-PSS shows doping levels which trebles the unmodified material. On the other, the electron transfer constant and the true electroactive area for ferrocene oxidation increased by a factor of 2 and 4, respectively.

A study on the electrochemical oxidation of piperazine and its electrochemical copolymerization with aniline in acidic medium is presented. It was found that the homopolymerization of piperazine cannot be achieved under electrochemical conditions. A combination of electrochemistry, in situ Fourier transform infrared (FTIR), and ex situ X-ray photoelectron spectroscopy (XPS) spectroscopies was used to characterize both the chemical structure and the redox behavior of an electrochemically synthesized piperazine–aniline copolymer. The electrochemical sensing properties of the deposited material were also tested against ascorbic acid and dopamine as redox probes.

The electrochemical copolymerization of aminoterephthalic acid and aniline can be achieved to yield a self-doped material showing electroactivity at physiological pH. The present study focusses on the management of the synthesis conditions to obtain a true copolymerization product and to control the relative amount of both comonomers eventually incorporated to the copolymer chain. Both, in situ FTIR spectroscopy and ex situ XPS techniques proved the successful incorporation of aminoterephthalic acid and, in parallel to other polyaniline parent derivatives, revealed the existence of redox transformations involving leucoemeraldine-emeraldine-pernigraniline transitions. The use of a high inversion potential (1.4 V/RHE) during electro-copolymerization resulted in a material enriched in aminoterephthalic acid fraction with respect to aniline, while this last component is favored at lower potentials. The pH behavior of copolymers in combination with in situ FTIR results strongly suggested that a larger content of aminoterephthalic acid (such as that obtained after deposition at 1.4 V) do not ensure an extensive self-doping process because a significant fraction of those carboxylic moieties remain inactive during the redox transformation. Instead, low inversion potentials are preferred to obtain a material with less defects and thoroughly electroactive at physiological pH.

The direct electron transfer (DET) to redox proteins has become a central topic in the development of biotechnological devices. The present work explores the mechanisms of the direct electrochemistry between cytochrome c (cyt c) and a conducting polymer, poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonate) (PEDOT–PSS). This polymer has been electrosynthesized from its monomers in aqueous solution on gold electrodes, and its capabilities for DET to cyt c have been examined by electrochemical and spectroelectrochemical methods. The polymer was electrodeposited with controlled thickness, and we determined that the electron transfer rate constant for cyt c oxidation was about 2 orders of magnitude higher than those obtained at conventional electrodes. Spectroelectrochemical measurements allowed us to evaluate the redox state of the polymer as a function of the potential and, in addition, the observation of intrinsic cyt c redox activity upon electron transfer from the conducting polymer. During the oxidation process of this protein, lysine residues placed near the heme crevice interact electrostatically with the anionic polyelectrolyte PSS. This interaction favors the orientation of the heme group toward the chains of the PEDOT backbone, which is eventually responsible for the electron transfer to the protein.

The electrochemical copolymerization of aminoterephthalic acid (ATA) and o-aminophenol (OAP) was carried out on platinum electrodes in acidic medium. The obtained material, poly(ATA-co-OAP), can be deposited by cyclic scanning of the potential in a wide potential range and shows significant electroactivity. However, it was observed that a copolymer with less overoxidation defects is obtained at inversion potentials where only OAP monomer (and not ATA monomer) is oxidized. The successful incorporation of unoxidized ATA monomers to the growing copolymer chain was confirmed by in situ FTIR spectroscopy and XPS, which suggested a monomer ratio close to 1:2 (ATA:POAP) within the obtained copolymer material. The redox switching of poly(ATA-co-OAP) in acidic medium involves reversible benzenoid-quinoid and phenoxazine-phenoxazone conversions but carboxylic groups do not participate actively on these transformations.

Poly(2-amino-4-tert-butylphenol), poly(2A-4TBP), was synthesized from monomer aqueous solution using either electrochemical or chemical oxidation procedures. Several spectroscopic characterization techniques were employed to gain information on the chemical structure and redox behavior of the obtained materials. It was found that the chemical polymerization product could be described as an oligomer mixture containing up to 16 monomer units. In parallel to other polymers derived from o-aminophenol, phenoxazine rings constitute also the basic structure of poly(2A-4TBP). In addition, the occurrence of N-N couplings, which are favored by the presence of the voluminous tert-butyl substituent, seems also relevant. No significant structural differences were found between the chemically or electrochemically synthesized materials.

Polypyrrole (PPy) was synthesized by enzyme mediated oxidation of pyrrole using naturally occurring compounds as redox mediators. The catalytic mechanism is an enzymatic cascade reaction in which hydrogen peroxide is the oxidizer and soybean peroxidase, in the presence of acetosyringone, syringaldehyde or vanillin, acts as a natural catalysts. The effect of the initial reaction composition on the polymerization yield and electrical conductivity of PPy was analyzed. Morphology of the PPy particles was studied by scanning electron microscopy and transmission electron microscopy whereas the chemical structure was studied by X-ray photoelectron and Fourier transformed infrared spectroscopic techniques. The redox mediators increased the polymerization yield without a significant modification of the electronic structure of PPy. The highest conductivity of PPy was reached when chondroitin sulfate was used simultaneously as dopant and template during pyrrole polymerization. Electroactive properties of PPy obtained from natural precursors were successfully used in the amperometric quantification of uric acid concentrations. PPy increases the amperometric sensitivity of carbon nanotube screen-printed electrodes toward uric acid detection.

The conducting self-doping copolymer poly(aniline-co-ABA) preserves its redox activity at pH values as high as 7. This observation was the starting point to synthesize an organic–inorganic hybrid composite able to electrochemically oxidize ascorbic acid molecules at that pH. The inorganic part of the catalytic element was an ordered mesoporous electrodeposit of SiO2, which has been used as the template for the electrochemical insertion of the self-doping copolymer. The oxidation of ascorbate ions at a fixed potential on this composite was studied by means of the kinetic model proposed by Bartlett and Wallace (2001). It was observed that the effective kinetic constant KME increased significantly but, simultaneously, k′ME remained almost constant when the composite was employed as the electrocatalytic substrate. These results were interpreted in the light of two combinations of kinetic constants, which strongly suggested that the increase in KME should be ascribed to the improvement in electronic conductivity of the copolymer induced by the highly ordered silica template.

Porous, electrically insulating SiO2 layers containing polystyrene sulfonate (PSS) were deposited on glassy carbon electrodes by an electrochemically assisted deposition method. The obtained material was characterized by microscopic, spectroscopic and thermal techniques. Silica-PSS films modify the electrochemical response of the glassy carbon electrodes against selected redox probes. Positively charged species show reduced diffusivities across the SiO2-PSS pores, which resulted in a concentration ratio higher than 1 for these species. The opposite behaviour was found for negatively charged redox probes. These observations can be interpreted in terms of the different affinity of the GC/SiO2-PSS-modified electrode for the electroactive species, as a consequence of the negatively charged porous silica.

The direct electron transfer between indium–tin oxide electrodes (ITO) and cytochrome c encapsulated in different sol–gel silica networks was studied. Cyt c@silica modified electrodes were synthesized by a two-step encapsulation method mixing a phosphate buffer solution with dissolved cytochrome c and a silica sol prepared by the alcohol-free sol–gel route. These modified electrodes were characterized by cyclic voltammetry, UV–vis spectroscopy, and in situ UV–vis spectroelectrochemistry. The electrochemical response of encapsulated protein is influenced by the terminal groups of the silica pores. Cyt c does not present electrochemical response in conventional silica (hydroxyl terminated) or phenyl terminated silica. Direct electron transfer to encapsulated cytochrome c and ITO electrodes only takes place when the protein is encapsulated in methyl modified silica networks.

The electroassisted encapsulation of Single-Walled Carbon Nanotubes was performed into silica matrices (SWCNT@SiO2). This material was used as the host for the potentiostatic growth of polyaniline (PANI) to yield a hybrid nanocomposite electrode, which was then characterized by both electrochemical and imaging techniques. The electrochemical properties of the SWCNT@SiO2-PANI composite material were tested against inorganic (Fe3+/Fe2+) and organic (dopamine) redox probes. It was observed that the electron transfer constants for the electrochemical reactions increased significantly when a dispersion of either SWCNT or PANI was carried out inside of the SiO2 matrix. However, the best results were obtained when polyaniline was grown through the pores of the SWCNT@SiO2 material. The enhanced reversibility of the redox reactions was ascribed to the synergy between the two electrocatalytic components (SWCNTs and PANI) of the composite material.

Composite materials made of porous SiO2 matrices filled with single-walled carbon nanotubes (SWCNTs) were deposited on electrodes by an electroassisted deposition method. The synthesized materials were characterized by several techniques, showing that porous silica prevents the aggregation of SWCNT on the electrodes, as could be observed by transmission electron microscopy and Raman spectroscopy. Different redox probes were employed to test their electrochemical sensing properties. The silica layer allows the permeation of the redox probes to the electrode surface and improves the electrochemical reversibility indicating an electrocatalytic effect by the incorporation of dispersed SWCNT into the silica films.

The electrochemical homopolymerization of o-aminobenzoic acid has been performed on both gold and graphite surfaces in perchloric acid aqueous medium by cyclic scanning of the potential. Electroactive polymeric materials are formed in all cases but the amount of electropolymerization products seems to be increased by the graphite carbon electrodes. The polymers obtained have been characterized electrochemically. In addition, in situ FT-IR spectroscopy and scanning electron microscopy were combined to study the redox behaviour of the oxidation products and the surface morphology of the coatings. Characteristic absorption features related with benzenoid and quinoid rings and different types of C–N bonds point to the operation of redox processes similar to those undergone by the parent compound polyaniline. Owing to the presence of the –COOH group in the carbon backbone, polymer films obtained from o-aminobenzoic are, contrary to polyaniline, electroactive at pH values over 3. Besides, it was observed that repeated oxidation–reduction cycles in working solutions with pH above 6 led to the dissolution of the deposited material.

Es bien conocido que mientras que en disoluciones con pH menor de 3 el monómero de anilina polimeriza electroquímicamente, obteniéndose como resultado de esa polimerización el polímero conductor conocido como Polianilina, en disoluciones con pH superior a 3 la polimerización electroquímica del monómero conduce a la formación de un polímero no conductor. Sobre esta base, se ha realizado un trabajo de investigación fundamental cuyos objetivos principales fueron: investigar tanto las homopolimerizaciones como las co-polimerizaciones electroquímicas de los dímeros de anilina sin sustitución, 4-adpa y 2-adpa, y de las anilinas sustituidas, dpasa(ácido difenilamino sulfónico)y dtda (ditiodianilina). Analizando el efecto del pH tanto en las reacciones de electropolimerización como en el comportamiento electroquímico de los materiales sintetizados y el efecto que produce el potencial límite anódico en la electropolimerización. Estudiar el posible efecto electrocatalítico de los polímeros conductores obtenidos sobre la oxidación/reducción de una serie de moléculas orgánicas e inorgánicas. Así como la capacidad sensora del poli(dtda).

The electrochemical oxidation of the aniline dimers 2-aminodiphenylamine (2-adpa) and 4-aminodiphenylamine (4-adpa) has been performed in strongly acidic medium on platinum, graphite, and indium tin oxide electrodes. The resulting films have been characterized by a number of electrochemical, microscopic, and spectroscopic techniques in order to gain some insight on their respective chemical structures. Both poly(2-adpa) and poly(4-adpa) are electroactive species which differ significantly one from another. It was found that aged poly(4-adpa)displayed electrochemical, morphologic and spectroscopic characteristics similar to those shown by polyaniline. On the contrary, poly(2-adpa) is really a mixture of three oligomerization products. The two main oligomers contain both open-ring and cycled phenazine centers, although their chemical structures seem to differ in the cap-end of the chain growth. The third oligomer is a minor product which seems a highly symmetric macrocycle involving several 2-adpa molecules.

This communication deals with the vibrational behaviour of cyanide adlayers formed on Pt(111) and Pt(100) surfaces in the electrochemical environment. In situ FTIR spectroscopy can be employed to follow the potential dependence of the C–N stretching frequency in acidic electrolytes with quite a low uncertainty. Owing to the stability of the cyanide adlayer in alkaline solutions, experiments performed in NaOH medium are usually perturbed by the significant overlapping of the reference and the sample FTIR spectra. Deconvolution of the spectra was carried out assuming a Lorentz oscillator. The procedure allowed to confirm that two potential regions with different band centre frequency tuning coexist for Pt(111)–CN in perchloric acid medium. Conversely, in the alkaline electrolyte a single tuning rate for the band position was found for both surfaces studied. The lack of reorientation of the C–N molecular axis together with the occurrence of a certain screening effect of negatively charged hydroxyl anions on the electric field at the interface could be at the origin of the different behaviour displayed in both electrolytic media.

The redox process undergone by the electrochemically synthesized poly(2,2-dithiodianiline), poly(DTDA), has been examined in acetonitrile-water mixtures by electrochemical and spectroscopic techniques. The spectroscopic properties of this material are equivalent to those exhibited by the chemically synthesized one. The polymeric structure displays a ladder structure, with S-S bonds serving as interconnections between two adjacent polyaniline chains. The kinetic reversibility of the RS–SR <=> 2RS− reaction is very poor for the DTDA monomer species, and this irreversibility is retained in the polymeric material. According to the results presented, the hypothesis that poly(DTDA) could display a high energy density due to the simultaneity of the leucoemeraldine <=> emeraldine and dithiolate <=> disulfide electrochemical transformations does not seem justified.

The electrochemical oxidation of 2-aminodiphenylamine (2ADPA) was performed by cyclic scanning of the potential in aqueous HCl solutions. A mixture of oligomeric compounds, named poly(2ADPA), was deposited on the surface of the electrode. The chemical structures present in poly(2ADPA) containing phenazine units and open-ring units were assigned by 1H NMR spectroscopy. CV results revealed that the redox transformation of poly(2ADPA) from the fully reduced to the fully oxidized state occurs under a single voltammetric peak. The SEM images obtained for the polymer deposited on platinum substrates showed a “fallen leaves” morphology. In situ FTIR spectroscopy experiments carried out during the reversible oxidation of the polymer revealed that the conversion of aromatic rings (1500 cm−1) into quinoid structures (1524–1590 cm−1) is of major significance. Besides, the transformation of secondary aromatic amines (1301 cm−1) into fully oxidized imines and polaronic structures (1470, 1389, 1330 and 1250 cm−1) has been observed.

Hybrid material polypyrrole/PW12O-340 was electrosynthesised on carbon steel electrodes in acetonitrile medium. Passivation pretreatment of carbon steel in acetonitrile/perchlorate medium was used to avoid electrodissolution of electrode during the polymerisation. These hybrid coatings were evaluated against corrosion in chloride-containing 0.05 M NaOH and solutions obtained by filtering Portland cement slurries. Cyclic voltammetry, polarisation resistance(Rp), and Fe2+ concentrations measurements showed that the obtained coatings provide good protection against corrosion in chloride-containing media.

The electrocatalytic behaviour of poly(aniline-co-4adpa), Pan-4adpa, films against some redox couples and ascorbic acid was tested in aqueous buffering solutions of pH = 5. The film catalysed the redox process of all the couples investigated although it has been observed that positively charged species such as dopamine/dopaminequinone display more irreversible voltammetric behaviour than negative (ferro/ferricyanide) or neutral (hydroquinone/quinone) ones. The voltammetric results point that the catalytic sites of the Pan-4adpa are probably located at the surface of the film. The oxidation peak of ascorbic acid on Pan-4adpa films is shifted 170mV to more cathodic potentials with respect to the Pt with no generation of adsorbed residues.

The adsorption and reactivity of citrate anions, cyanide anions, and the Au(I) and Au(III) cyanocomplexes (KAu(CN)2 and KAu(CN)4, respectively) on gold polycrystalline electrodes have been investigated by means of cyclic voltammetry and in situ FTIR spectroscopy in pH 7 sodium citrate medium. It was found that citrate anion adsorbs reversibly through the carboxylate groups from 0.4 V (RHE) on bare gold surfaces. However, the onset of this adsorption process is shifted by 600 mV in the positive direction when adsorbed cyanide species are present at the electrode surface. The Au(I) cyanocomplex produces a film on the gold electrode that inhibits the oxidation of both citrate anions and the gold surface. The reduction of the Au(III) cyanocomplex gives rise to the formation of the Au(I) cyanocomplex at potentials less negative than those required for gold deposition. Upon reduction, both cyanocomplexes release adsorbed cyanide on the gold electrode, which can be subsequently oxidized to cyanate at higher potentials.

The electrochemical oxidation of p-aminodiphenylamine (4ADPA) in the presence of aniline in phosphate medium of pH ranging from 1 to 10.5 has been investigated. Mixtures of both monomers can be co-polymerized to produce electroactive poly aniline-co-4ADPA (Pan-4adpa) films if the pH of the medium is kept, approximately, within 3 and 9 and the upper potential limit is lower than the oxidation potential of aniline. Pan-4adpa growth rates are pH dependent and are also affected by the amount of polymeric material deposited on the electrode surface. It has been suggested the existence of a certain inhibition effect of both H+ and OH− on the polymerization reaction. Contrary to what is observed for those films synthesized at pH 5 and 7, the growth of Pan-4adpa at pH 8 seems to be an autocatalytic process until the inhibition of the polymerization reaction takes place.

The electrochemical homo-polymerization of o-, m- and p-aminobenzoic acids has been performed on Pt electrodes in perchloric acid aqueous medium by cyclic scanning of the potential. Different limit potentials were employed to obtain thin polymeric films. When the switching potential was extended beyond the respective monomer oxidation peak, a rather degraded material was obtained. In situ FTIR spectroscopy has been used to characterize the redox response of films synthesized at the lower potential limits. Characteristic absorption features related with benzenoid and quinoid rings and different types of C–N bonds suggest the presence of redox processes similar to those undergone by the parent compound polyaniline. In addition, the existence of a chemical interaction between –COOH and –NH– groups in the reduced state of the three homopolymers studied can be suggested. Carbon dioxide has been detected at potentials higher than 1.0 V (RHE) irrespective of the polymeric material, thus indicating its degradation.

The electrochemical oxidation of aniline and p-aminodiphenylamine (ADPA) was carried out in a phosphate buffer solution at pH 5. Cyclic voltammetry and ‘‘in situ’’ FTIR spectroscopy were combined to study the redox behavior of the oxidation products. When ADPA is oxidized in the presence of aniline, two redox processes are observed. One of these redox processes is related to a soluble species, while the other pertains to a species attached to the electrode surface. Only those films synthesized from ADPA oxidation in the presence of aniline are electroactive in this buffered medium. No evidence pointing to the occurrence of autocatalytic polymerization exists under the experimental conditions employed.

Carbon monoxide has been adsorbed at controlled potential on a Pt(111) electrode, which was pre-covered with cyanide up to saturation. From the results obtained, it has been deduced that CO occupies platinum sites between CN molecules with no distortion of the pre-adsorbed cyanide layer. The anodic stripping of CO does not induce modifications of the CN adlayer either. These observations allow the estimation of hCO rather accurately by means of the coulometric method.

The electrochemical oxidation of aniline at low concentration was carried out in phosphate buffer solutions of pH 5. Both electrochemical and spectroscopic results indicate that during the initial stages of aniline oxidation, a dimerisation process takes place. The dimer has been identified as p-aminodiphenylamine (ADPA). No evidence supporting the formation of other dimerisation products, such as benzidine or hydrazobenzene has been found. The hydrolysis of ADPA seems to be a very slow process at pH 5 and, consequently, the formation of hydroquinone/p-benzoquinone has not been observed. ADPA is poorly soluble in aqueous medium and a part of these species precipitates on the electrode surface when formed. This precipitated dimer could act as an active centre for the further growth of the polymeric chains.

In contrast to what is observed in alkaline media, cyanide adlayers formed on Pt(100) are very reactive in 0.1 M HClO4 solutions. In this medium, dissimilar behaviour has been observed for the potential regions above and below 0.4 V (RHE). CNads is oxidised above 0.8 V to form dissolved CO2 and an adsorbed nitric oxide layer. Two distinct absorption frequencies have been observed for the N–O stretching at 1610 and 1680 cm−1. On the other hand, CNads is able to react below 0.4 V to yield an adsorbed carbon monoxide adlayer. The reaction rate is slow enough to allow the observation of a surface intermediate species by means of in situ FT IR spectroscopy. As deduced from the analysis of the spectra, this species may contain a double C-N bond (i.e. an iminium-like adsorbed residue).

The electro-reduction of SO2 has been monitored by using cyclic voltammetry, FT-IR spectroscopy and SER spectroscopy. Prior to the bulk reduction, SO2 is reduced to yield a monomeric sulphur adlayer at a maximum coverage of about 0.25. The sulphur adlayer undergoes a reversible redox surface process at E<0.0 V (RHE), which implies a change in the frequency of the Au-S stretching mode from 270 to 300/310 cm−1. In the potential region encompassing the bulk reduction voltammetric peak, infrared spectra display a band at 2585 cm−1 attributable to a S-H vibration from a soluble species. Accordingly, H2S or H2Sx were proposed as tentative bulk reduction products. In positive sweeps a broad anodic wave develops between 0.2 and 0.6 V that leaves polymeric sulphur species adsorbed at multilayer level, with a S-S stretching mode at 460 cm−1 and a S-S-S bending vibration at 218 cm−1. Multilayer sulphur can be removed reductively under a sharp cathodic peak. According to literature of the S(-II)/Au system, removal proceeds to yield soluble S(-II) species, via intermediate polysulphides.