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Graphitized Carbon Nanofibers (GANFg) were dispersed with a certain amount of organic expander and used as additive for the negative plates of the Lead Acid Batteries (LABs). Due to the high aspect ratio of these fibers, they are thought to reach the percolation threshold inside the Negative Active Material (NAM) and create a conductive network which would improve the cycle life of the LABs working in Partial State of Charge (PSoC) conditions. These fibers were added at three concentrations (0.50, 0.20 and 0.10 wt. %) and dispersed in a sodium lignosulfonate aqueous solution. Unformed negative plates of three mixtures were prepared, together with a NAM Control sample, and 2 V/1 Ah small lead acid cells were assembled for testing the electrical performance of the different mixtures (capacity, cold cranking ability, charge acceptance, negative polarization study, PSoC cycles and Cyclic Voltammetry (CV)). Continuous physicochemical analysis was carried out for the negative plates. As a result, Carbon Nanofibers were able to increase cell cycle life working in PSoC conditions and slightly improve the charge acceptance, but also raised the water loss. However, this gassing increase was lower for Carbon Nanofibers in comparison with other carbon materials used in flooded LABs.

Lead-Acid batteries have been in continuous upgrade as they are required for new applications, such as stop-start function and regenerative braking for Micro-Hybrid vehicles. These issues are closely linked to cyclability and charge acceptance whose failure is directly related to a high sulfation of the negative plates. Carbon materials can be added to the negative active material to delay this sulfation, and other organic compounds, such as lignosulfonates, take part also in the improvement of these features. In this study, different types of carbon materials and lignosulfonates were used as additives for the negative active material, and negative plates have been prepared to assembly 2 V/1 Ah small lead acid cells. The cells performed several electrical tests: capacity, cold cranking, initial charge acceptance test, negative polarization study and cycling life in Partial State of Charge. At the same time, continuous physicochemical analyses of negative plates were carried out in order to evaluate their structure and composition. As a conclusion, those carbon materials that were are able to be introduced into the lead skeleton showed performance on charge acceptance by acting as super-capacitors, and on cycle life by reducing negative plate sulfation. The carbon material that was able to remain on the lead surface was able to increase charge acceptance, but failed to complete the cycle life test due to a high sulfation on its negative plates. The type of lignosulfonate and the electrochemical surface area supplied with the carbon materials had a strong influence on hydrogen evolution.

The electrochemical C-H functionalization of carbamates via N-acyliminium ion is a very useful way for synthesizing biologically active and pharmaceutical products but its mechanism is not fully understood yet, specially referring to the anomalous regioselectivity that leads to the functionalization in the less substituted site which would allow to modulate the regioselectivity of the process in the asymmetric carbamates. Cyclic voltammetry experiments (with both static and rotating disk electrode) of the α-alkoxylation of carbamates prove that the mechanism for this reaction is of the type ECEC with the first two steps occurring in a concerted manner, a conclusion that is also corroborated by theoretical (DFT) values of absolute redox potentials. Further theoretical calculations show that the cause of the anomalous regioselectivity lies in the combination of the dipole moment vector of the asymmetric carbamates with the concerted ECEC mechanism.

To develop new materials for Al/air batteries, the evaluation and characterisation of commercial aluminium alloys, namely, Al2000, Al2000Clad and Al7000, as anodes in alkaline electrolyte batteries has been performed. Their self-corrosion rate, hydrogen evolution rate and electrochemical properties, including open circuit potentials, polarisation characteristics and potentiodynamic measurements, were examined in a 4 M KOH solution. Among the tested alloys, Al2000 was found to be the most promising because it exhibits a high open circuit potential, a good anode efficiency and a minimum corrosion rate. Al2000/NiOOH and Al2000/air batteries were tested. Electrolyte concentrations between 0.01 and 4 M KOH were studied, and discharge currents between 0.8 and 20 mA cm−2 were imposed to analyse the evolution of the Ecell. Conversely, the Al7000 alloy exhibited the highest corrosion rate and H2 evolution compared to the other alloys.

Functionalized carbonaceous materials have been investigated as supports of PtRu nanoparticles for the electrooxidation of methanol, using such conventional electrochemical methods as cyclic voltammetry and chronoamperommetry and by measurements in a CH3OH/O2-fed single cell. Further, to understand the effect of oxygen-containing groups on the supports in the methanol oxidation reaction (MOR), a kinetic study of the catalyst that has the best behavior in this process has been performed. The study at different temperatures of PtRu nanoparticles supported in multiwall carbon nanotubes (MWCNTs) with a high amounts of functional groups—PtRuCNT-ST—show that there was low CO poisoning during the MOR on this catalyst. The low apparent energy on PtRuCNT-ST in the MOR was attributed to CO diffusion or to the dissociative adsorption of methanol. Both factors had a beneficial effect on the oxygen-containing groups on MWCNTs, facilitating oxidation of the carbonaceous intermediates to CO2 or HCOOH. These findings have been confirmed by studies in a single cell feeding with CH3OH/O2, demonstrating that PtRuCNT-ST is the best-performing anodic electrode.

The possibility of using TTF-derivatized SAMs as platforms for the construction of electrochemical biosensors is explored. The properties and characteristics of the electroactive SAMs formed with 4-mercaptotetrathiafulvalene (HSTTF) and 4-(mercapto-ethan-2-thiol)-tetrathiafulvalene (HSC2STTF), and their ability to promote the electron transfer between the active center of the immobilized enzyme, HRP, and the electrode surface is evaluated. Calculations from electrochemical impedance spectroscopy data showed a microarray behavior for HSC2STTF-SAMs. However, semi-infinite diffusion was not obtained for HSTTF-SAMs. The slope value of the H2O2 calibration plot obtained by flow-injection with amperometric detection at 0.00 V was more than one order of magnitude higher with the HSTTF design, which is attributed to the larger number of TTF moieties present at the electrode surface. The performance of the bioelectrocatalytic integrated devices is shown to be very dependent on the molecular structure of the TTF derivative. Keywords: Electroactive self-assembled monolayers, Tetrathiafulvalene, Integrated biosensors, Horseradish peroxidase

The structure and electrochemical properties of pure and mixed monolayers of 3-mercaptopropionic acid (MPA) and 11-mercaptoundecanoic acid (MUA) self-assembled on a gold disk electrode (AuE) have been investigated by electrochemical impedance spectroscopy (EIS) in electrolytes containing a one-electron redox couple. These results are compared with those obtained by cyclic voltammetry (CV). The monolayer surface coverage was determined using impedance measurements through the charge-transfer resistance, and by the pore size model. Cyclic voltammetry considering gold oxide formation/removal, as well as the oxidation/reduction process of a redox probe, was also employed to calculate the surface coverage. Taking into account the stability of the studied monolayers during the electrochemical experiment, the comparison of the barrier to charge transfer at both, the modified and the unmodified electrodes, resulted to be an appropriate method for estimating the surface coverage percentage given by each of the considered monolayers. The obtained results demonstrated that the MPA-monolayer-coated electrode behaves like a microelectrode array, with pinholes acting as the microelectrodes. The average size and the separation of the pinholes, estimated by the pore size model, are 1.9 and 21 μm, respectively. However, MUA forms a closely packed monolayer that acts as an ionic insulator and is virtually defect-free. The adsorption kinetics of MPA and MUA SAMs on the gold electrode (AuE) was evaluated. As expected, mixed monolayers of MPA and MUA show characteristics of both, long and short-chain alkanethiol monolayers.

Electroactive polymer films of polyaniline, poly-o-toluidine and a composite of both were deposited on stainless steel and their performance as protective coatings against corrosion was evaluated. Open circuit potential and potentiodynamic studies of the polymer-coated stainless steel in a corrosive medium showed a significant shift in the corrosion potential towards more positive values. Mechanical characteristics of the films were evaluated by means of microhardness measurements, revealing nonelastic films in all cases and low hardness values that increased from polyaniline to poly-o-toluidine to the composite. The best results were obtained in the case of the polyaniline-o-toluidine composite.

Three different strategies for cucurbit[8]uril immobilization on a glassy carbon electrode have been assayed. The electrochemical properties of the resulting modified electrodes in solutions containing neutral, positively and negatively charged potential cucurbit[8]uril guests were investigated by cyclic voltammetry and electrochemical impedance spectroscopy. The comparison of the electrochemical behaviour exhibited by the unmodified electrodes against various probes, with respect to that of each modified electrode, resulted in an appropriate method to choose among different strategies for the development of electrochemical sensors. These sensors are based on the incorporation of the cucurbit[8]uril molecular selection properties that depend on the chemical characteristics of the potential analytes. Furthermore, atomic force microscopy was employed for the characterization of the different surfaces developed.

An experimental study of the influence of low frequency in demodulation voltammetry has been carried out for the reduction of Cd(II) in NaClO 4 . From the variation of both in-phase and quadrature components of the demodulation response, the more adequate frequency range where it is convenient to do the measurements is deduced. Likewise, a simple method of analysis to obtain the kinetic parameters of the system is presented. This method is based on the low frequency variation, the previous assumption of a reaction mechanism not being necessary.

The impedances of conducting polypyrrole films, which were prepared electrochemically, were measured. The measured impedance shows a strong anisotropy of the capacitance in directions parallel and perpendicular to the substrate. A similar observation was made with respect to resistivity. In order to interpret these results, a model is proposed which is in agreement with experimental data.

The hydrogen reactions on polycrystalline Pd in 0.1 M NaOH at 25°C have been studied by using transients at constant potential, and by impedance spectroscopy and X-ray diffraction techniques. At potentials, Es, more positive than the reversible potential, Er, for the H2 evolution reaction, the current-time response and the impedance data indicate H atom diffusion into the bulk Pd. The X-ray diffraction pattern of electrodes cathodized during 20 min at these potentials are similar to those obtained for Pd. At Es

A secondary battery of the type , carbon is described. The polymer was electrodeposited on porous carbon rods, in the form of consistent, rather thick, highly porous, and low‐resistance layers. The battery was assembled in a configuration similar to that of the classical R‐6 dry cell. The performance of the battery has been studied, and it shows characteristics comparable to those of conventional systems: moderate specific energy (50–100 Wh kg−1), very good coulombic efficiency (70–100%), low self‐discharge rate (

The hydrogen reactions on polycrystalline Pd in 0.1 M NaOH at 25°C have been studied by using transients at constant potential, and by impedance spectroscopy and X-ray diffraction techniques. At potentials, Es, more positive than the reversible potential, Er, for the H2 evolution reaction, the current-time response and the impedance data indicate H atom diffusion into the bulk Pd. The X-ray diffraction pattern of electrodes cathodized during 20 min at these potentials are similar to those obtained for Pd. At Es < Er, the current transients exhibit a current maximum which increases as Es moves in the negative direction. The Nyquist plot for the rising part of the transients indicates the H atom diffusion into the bulk metal and H2 evolution on the Pd surface at high frequencies. The X-ray diffraction pattern of the electrodes cathodized at Es < Er, shows the presence of the βPdH phase and Pd. The experimental results indicate that different reactions take place simultaneously in this potential range: (i) Hs evolution, (ii) H diffusion into the bulk Pd, (iii) nucleation and diffusion-controlled growth of the βPdH phase. Taking into account the contribution of these reactions, a model, which is able to reproduce the experimental current transients, is presented., Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas

The electrodeposition of Mercury Cadmium Telluride (Hg1-x Cd x Te), with a variable amount of mercury, on SnO 2 substrates is studied. The effect of different postformation thermal treatments under several atmospheres, on the crystalline structure, optical and electrical properties of the electrodeposited films is described.

Flat band potentials ( V fb ) of In 2 S 3 polycrystalline thin films obtained by chalcogenization of electroplated metallic indium films on Ti substrates with a flowing stream of H 2 S gas have been obtained. The variation of this potential with different redox couples, solution concentration and pH values has been studied. Photoelectrochemical characterization of the electrodes was accomplished in aqueous polysulphide solutions and the application of the Gartner—Butler model to the semiconductor/electrolyte interface makes it possible to obtain the semiconductor energy gap. The value obtained is 2.06 eV, corresponding to a direct allowed transition.

The reduction of In(III) in solutions containing 0.5, 0.75 and 1 M of NaI and with an ionic strength of 1.00 maintained with sodium perchlorate, has been studied by measuring the interfacial admittance spectra at different dc potentials of the dropping mercury electrode ( dme ). The frequency dependence of the admittance corresponds to that of a reversible electrode reaction with reactant adsorption. The adsorption parameters have been determined and the strange behaviour of u′ , which increases with cathodic potential must be pointed out. This seems to indicate that the adsorption occurs beyond the potential at which begin the reduction of indium. It is shown that the potential dependence of the adsorption parameters can be mathematically described by a Langmuir isotherm with the adsorption free energy being at least a quadratic function of potential. Strong adsorption effects have not been found.

The effect on the stoichiometry of a copper sulphide electrode of short-circuiting the Cu/Cuaq2+/Cu2-δS/In galvanic cell for different times has been studied. This treatment has been carried out on the copper sulphide layer of CdS/Cu2S solar cells prepared by different methods. The resulting changes of the spectral short circuit current and the I–V characteristics of the cells have been recorded. Remarkable increases in open circuit voltage, short circuit current, and fill factor have been observed as a consequence of any transformation that increases the proportion of copper in the copper sulphide films. Thus, this treatment could be a suitable method of improving the efficiency of CdS/Cu2S solar cells.

The influence of specific adsorption of electroactive species on the polarographic determination of stability constants is studied quantitatively. An expression for the term that permits correction of the effect of the adsorption and the “true” value of the constants to be obtained from the “apparent” value is deduced. The sense of the correction shows that the “apparent” constants are always higher than the “true” ones, which is in agreement with some experimental observations. Analysis of the dependence of the correction term on the adsorption parameters shows that even moderate adsorption exerts a significant influence on the values of the stability constants.

The reduction of In(III) in solutions containing 0.05, 0.1 and 0.25 M of NaI and with an ionic strength of 1.00 maintained with sodium perchlorate, has been studied by means of interfacial admittance measurements at different frequencies and dc potentials of the dropping mercury electrode. Our results demonstrate that the process takes place with specific adsorption of electroactive species. The adsorption parameters and their dependence with potential have been determined. From the analysis of our results, together with those obtained in a previous study at higher concentrations of I − , it can be deduced than InI + 2 is the species preferentially adsorbed, this adsorption taking place via a bridge-like mechanism, through I − ions previously adsorbed.

Cadmium sulphide films are electrodeposited from dimethylsulphoxide (DMSO) and propylene carbonate (PC) on stainless steel and tin oxide substrates. The physical properties of the films grown in both solvents have been studied. The thickness, grain size and morphology of the CdS films have been examined using X-ray diffractometer patterns and scanning electron microscopy. Heat treatment in argon atmosphere improves the electrical conductivity of the samples.

The formation of copper sulphide thin films on copper substrates has been studied. The method of preparation is based on a chemical bath deposition process during which a cathodic potential is applied to the substrate. The composition, optical and electrical characteristics have been measured and their variation with the applied potential is analysed. The film obtained when the appropriate potential value was applied to the substrate was confirmed by transmission electron diffraction (TED) studies to be chalcocite.

The formation of cadmium sulfide thin films by cathodic deposition of Cd2+ ions from a solution containing sulfur on different substrates (platinum, molybdenum, aluminum) is described along with the influence of the substrate on the formation and morphology. By evaporating a layer on the films deposited on aluminum, a heterojunction which exhibits photovoltaic effect is formed.

The mechanism of electrodeposition of CdS on Pt and Au electrodes has been studied in proplyene carbonate solutions by performing cyclic voltammetry at stationary electrodes in solutions containing both Cd(II) ions and elemental sulphur. The formation of an initial layer of CdS by underpotential deposits of Cd reacting with chemisorbed sulphur is suggested. The growth of the films takes place afterward by reduction of sulphur to sulphide, which forms the deposit with Cd(II) from the solution.

The effects of thermal treatments on the stoichiometry and photovoltaic propierties of Cu x S thin films have been studied. It has been observed that the evaporation of a thin copper films on Cu x S, followed by thermal treatment in vacuum, improves the Cu x S CdS heterojunctions due to a rire in the stoichiometry and fill factor.