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[ES] El agua es uno de los recursos más valiosos del planeta, originando crisis allí donde la falta de la misma se hace notable. Es además un componente vital en la industria, formando parte como elemento fundamental de gran número de procesos. Estos alteran las condiciones del agua usada convirtiéndola en un residuo que debe ser expulsado del proceso. Es por tanto indispensable la puesta en práctica y el desarrollo de técnicas de limpieza de la misma de forma cada vez más efectiva., [CA] L’aigua es un dels recursos més valuosos del planeta, originant crisi enllà on la falta de d’aquesta es faja notable. Amés es tracta d’un component vital de la indústria formant part com element fonamental de gran nombre de processos. Aquests alteren les condicions del aigua usada transformant-la en un residu que ha de ser expulsat. Es per tant indispensable la posada en pràctica i el desenvolupament de tècniques de neteja de la mateixa de forma cada vegada més efectiva., [EN] Water is one of the most valuable resources on the planet, creating crisis wherever there is a notable lack of it. It is also a vital component in the industry, being a fundamental part in a big number of processes. These processes alter used water conditions transforming it into waste that must be eliminated from the process. Due to this, it is essential putting into practice and developing effective water cleaning techniques.

The graphite removal and the chemical oxygen demand (COD) reduction by the electrochemical treatment of an effluent containing a lubricant (oil in water emulsion with graphite) was investigated. The electrochemical cell used a pair of aluminum plates. Since the effluent conductivity was very low, NaCl was used as supporting electrolyte and different current densities as well as different distance between the electrodes were applied. In lower current densities, higher chloride concentrations implied in smaller COD values. The same behavior was observed when electrode distance was decreased. All the tested conditions presented significant graphite removal and COD reductions larger than 94%

One of the most important measurement parameters in electrochemical impedance spectroscopy (EIS) is the perturbation amplitude. The optimum perturbation amplitude value corresponds with a balance between the signal-to-noise ratio improvement and the reduction of the harmonic generation due to nonlinear effects. Therefore, the optimum perturbation amplitude is the maximum amplitude that ensures a linear response of the system. Two strategies were considered in this work, i.e., a constant amplitude strategy and a frequency dependent amplitude strategy. On the one hand, for the constant amplitude strategy, the optimum perturbation amplitude for EIS measurements of an individual cell of a commercial PEM fuel cell stack was determined. In order to fulfill this aim, the impedance spectra (at different DC currents) of the individual cell of the commercial PEM fuel cell stack were measured using different perturbation amplitudes. The total harmonic distortion of the recorded voltage signal was determined in each case, applying a FFT based method. The optimum amplitude for each DC current corresponds to the amplitude that minimizes the critical total harmonic distortion value. On the other hand, for the frequency dependent amplitude strategy, the optimum amplitude at each frequency for EIS measurements of an individual cell of a commercial PEM fuel cell stack was determined.

Au nanoparticles (Au-NPs) were successfully synthesized and incorporated into the surface of a macroporous Ni electrode fabricated via galvanostatic electrodeposition at high current densities in order to produce hydrogen by means of alkaline water electrolysis. The developed electrodes were morphologically characterized by means of confocal laser scanning and field emission scanning electron microscopes. The electrocatalytic behaviour towards the hydrogen evolution reaction was studied by Tafel polarization curves and electrochemical impedance spectroscopy. It was clear that enlarging the real surface area of an electrode its catalytic activity was greatly enhanced. This improvement was further increased when Au-NPs were added to the macroporous Ni surface. In this case, the improvement was not only caused by enlarging the surface area but also by an improvement in the intrinsic catalytic activity of the alloy, as it was shown by the exchange current densities values, calculated from the real surface area.

Platinum is the electrode material with the highest catalytic activity for the hydrogen evolution reaction (HER). However, its high cost and scarcity are the two major barriers for its usage in the industrial alkaline water electrolysis, which requires searching for other cheaper and more available materials with good catalytic activity. Ni based materials have attracted more and more attention due to their good activity for the HER and sufficient corrosion resistance in alkaline solutions at considerable low cost. According to the Brewer intermetallic bonding theory, molybdenum alloyed with nickel (hypo hyper-d-electronic transition metal) could improve the intrinsic catalytic activity for the HER. In this work, Ni and NiMo metallic coatings were galvanostatically electrodeposited on a stainless steel AISI 304 substrate by means of the double template electrochemical process. The evaluation of these electrodes as H2-evolving cathodes was done in 30 % wt. KOH by pseudo-steady-state polarization curves and electrochemical impedance spectroscopy (EIS) at different temperatures. From Tafel curves results, it is shown that the NiMo electrodes have higher catalytic activity than Ni. On the other hand, from EIS results, it is possible to conclude that the NiMo electrodes showed higher intrinsic catalytic activity for HER than the pure Ni electrode as a consequence of alloying hypo hyper-d-electronic transition metals.

Despite the development and synthesis of new electrode materials for hydrogen generation in alkaline water electrolyzers has been a research topic widely exploited in the last years, stability tests on the obtained cathodes have been restricted to long-term potentiostatic/galvanostatic experiments which do not fulfil the real operating conditions that take place in those devices. In this work, two different Service Life Tests have been designed and implemented, aiming at including particular conditions (i.e. inverse polarity and short-circuit) in the durability and catalytic activity of cathode characterization. For this purpose, Ni/Cu bilayered porous electrodes were prepared using different Ni electrodeposition times (15, 30 and 45 min) following a double template electrochemical method. It has been confirmed that the electrode with the lowest Ni content can be considered as a promising electrocatalyst for hydrogen production under industrial conditions because of its optimal activity and stability after the two sets of testing conditions. In particular, electrochemical studies demonstrated that an inversion in polarity can positively affect the electrode performance, as a consequence of the synergetic interaction between CuO/Cu(OH)(2) and beta-Ni(OH)(2) species formed at potentials below the oxygen evolution domain.

This work deals with the analysis of an integrated zinc recovery process by means of electrowinning of the stripping solutions coming from the treatment of spent pickling baths (SPB) by a membrane-based solvent extraction (MBSX) process able of increasing the initial Zn/Fe molar ratio. Several stripping solutions containing different concentrations of zinc and iron in acid media obtained previously by the treatment of SPB by MBSX, were subjected to electrowinning to assess the efficiency and selectivity of zinc electrodeposition over iron under different operation conditions. At similar values of the zinc concentration in the stripping solution, the influence of the Zn/Fe molar ratio on the zinc electrodeposition process was negligible. On the other hand, although the variation of the initial concentration of zinc in the stripping solution neither affected the efficiency of zinc electrowinning, it increased the minimum value of zinc concentration in solution beyond which iron co-deposition started. Finally, the increase in the applied current, promoted the increase in zinc fractional conversion and in the zinc space-time yield, while the zinc current efficiency was reduced due to the stronger effect of secondary reactions. Although the change in the stripping characteristics seems not to strongly affect the zinc electrodeposition process, the use of a pretreatment step based on MBSX technology improved the results in terms of zinc percentage recovered and the rest of figures of merit, in comparison with those obtained by the direct electrowinning of SPB. (C) 2015 Elsevier B.V. All rights reserved.

La presente Tesis Doctoral consiste en la determinación de las propiedades de transporte de diferentes especies catiónicas a través de membranas de intercambio catiónico. Las membranas de intercambio iónico son un componente clave de los reactores electroquímicos y de los sistemas de electrodiálisis, puesto que determinan el consumo energético y la eficiencia del proceso. La utilización de este tipo de membranas para el tratamiento de efluentes industriales no es muy extendida debido a los requisitos de elevada resistencia química y durabilidad que deben cumplir las membranas. Otro asunto importante radica en la eficiencia en el transporte de los iones que se quieren eliminar a través de la membrana. Normalmente, existe una competencia por el paso a través de las membranas entre diferentes especies debido al carácter multicomponente de los efluentes a tratar. Sin embargo, una mejora en las propiedades de las membranas de intercambio iónico permitiría la implantación del tratamiento mediante reactores electroquímicos de efluentes industriales con un contenido importante en compuestos metálicos, tales como los baños agotados de las industrias de cromado. La utilización de una tecnología limpia como la electrodiálisis conllevaría diferentes ventajas, entre las cuales destacan la recuperación de los efluentes para su reutilización en el proceso industrial, el ahorro en el consumo de agua y la disminución de la descarga de contaminantes al medio ambiente. La determinación de las condiciones de operación óptimas así como la mejora de las propiedades de transporte de las membranas constituye el principal tema de la presente investigación. Para ello, se emplearán diferentes tipos de membrana. En primer lugar, se estudiará el comportamiento de las membranas poliméricas comerciales que poseen unas propiedades de resistencia química elevadas, las cuales se tomarán como referencia. De forma paralela, se producirán membranas conductoras de iones a partir de materiales cerámicos

Proyecto confidencial (Riunet)

Currently, electrochemical Impedance Spectroscopy (EIS) is a widely used tool for the study of electrochemical systems, in general; and fuel cells, in particular. A great effort is typically invested in the analysis of the obtained spectra; whereas, little time is usually spent optimizing the measurement parameters used to obtain these spectra. In general, the default settings provided by the control software used to perform the measurements, or the parameters used in similar systems available in literature, are selected to carry out the measurements. The goal of this work is to determine the optimal measurement parameters for obtaining impedance spectra of a commercial PEM fuel cell. In order to achieve this, a 2^5 factorial design was considered. Five factors were considered, the five impedance spectroscopy measurement parameters: maximum integration time; minimum number of integration cycles; number of stabilization cycles; maximum stabilization time; and minimum cycle fraction. For each factor combination envisaged in the experimental design, the cell spectrum was obtained in given operation conditions, for which the reference spectrum of the system was known, since it had been determined in previous works. The experimentally obtained spectra were fitted to the reference electric equivalent circuit. The mean square error between the experimental data fitting and the reference spectrum fitting was determined in each case, and was used as the dependant variable for the experimental design analysis. An analysis of the variance was performed in order to determine which measurement parameters have a significant effect on the dependant variable; and a model relating the dependant variable and the measurement parameters was built. This model was used in order to obtain the optimal value of each one of the measurement parameters that minimized the mean square error of the fit obtained from the experimental data with respect to the reference fit.

An individual PEM fuel cell 6-parameter mechanistic model was developed. In parallel, experimental polarization curves were obtained at different temperature and inlet gas humidities conditions. The 6 model parameters were determined by fitting the semi empirical model to the experimental curve using a non linear regression method. Finally, a statistical analysis was carried out in order to determine which operating conditions (temperature and inlet humidities) have a significant effect on which model parameters. A black box model was built in order to relate the model parameter values to the significant operating conditions for each one of them. The obtained model was able to satisfactory reproduce the experimental behaviour of the system at low current densities.

Anion-exchange membranes made from inexpensive ceramic materials were synthesized by using a simple procedure based on incorporating particles of an ion exchanger into a host microporous structure. Microporous ceramics produced from alumina and kaolin were used as supports, and their internal voids were functionalized by direct precipitation of hydrated ZrO2. The addition of starch as pore former to the sintering mixture induces the formation of pores within the micrometer range, where the subsequent deposition of hydrated ZrO2 occurred preferentially. An increase in the loading of hydrated ZrO2 particles improved the ion exchange capacity (IEC) and induced anion-selective properties on the membranes. However, when more than six infiltration cycles were performed, the membrane porosity was substantially reduced. Electrochemical measurements conducted in acidic and neutral media corroborated the implication of the hydrated ZrO2 particles on the development of concentration polarization and confirmed the strong relationship existing between the membrane porosity and electrical conductivity. Conversely, chronopotentiometric curves showed that the membranes practically lack of ion-exchange properties when tested under alkaline conditions. The methodology proposed to synthesize ceramic ion-conducting membranes could significantly broaden the utilization of electromembrane processes in industrial applications where the use of polymeric membranes is restricted due to their expensive cost or poor chemical stability.

The use of electrochemical techniques in the selective recovery of gold from a solution containing thiosulphate, ammonia, and copper, obtained from the leaching of printed circuit boards from mobile phones using ammoniacal thiosulphate, are shown in this work. First, cyclic voltammetry tests were performed to determine the potential of electrodeposition of gold and copper, and then, electrowinning tests at different potentials for checking the rates of recovery of these metals were performed. The results of the cyclic voltammetry show that copper deposition occurs at potentials more negative than −600mV (Ag/AgCl), whereas the gold deposition can be performed at potentials more positives than −600mV (Ag/AgCl). The results of electrowinning show that 99% of the gold present in solutions containing thiosulphate and copper can be selectively recovered in a potential range between −400mV (vs Ag/ AgCl) and −500mV (vs Ag/AgCl). Furthermore, 99% of copper can be recovered in potentials more negative than −700mV (vs Ag/ AgCl)

Starch is used as porosity generator in membranes and other porous ceramics. A study was conducted to evaluate the effects of the characteristicsof starches (impurities, particle size), obtained from potato, pea, maize and wheat, on the properties of microfiltration membranes formulated withtraditional raw materials (the ceramic matrix was composed of quartz, albite and mullite). The results indicated that the pore size distributionand the permeability coefficient of the membrane can be controlled by modifying only the particle size of starch. In this way, correlations wereobtained between surface mean diameter of starch and membrane properties (characteristic pore diameters d16and d50, and permeability coefficient).Moreover, it is necessary to use a starch having a mean particle size greater than about 50 m in order to obtain a significant change in the poresize distribution and an increase in the permeability of the membrane

Electrochemical Impedance Spectroscopy (EIS) is a very powerful tool to study the behaviour of electrochemical systems. At present, it is widely used in the fuel cell field in order to study challenging cutting edge issues as membrane drying or gas diffusion layer flooding amongst others. The proper analysis of impedance data requires the fulfilment of four fundamental conditions: causality, linearity, stability and finiteness. The non compliance with any of these conditions may lead to biased, or even misguided, conclusions. Therefore it is critical to verify the compliance of these conditions before accepting any analysis performed on an experimental spectrum. This is even more important in a fuel cell experimental spectrum analysis, since fuel cells are markedly non stationary systems. The aim of this work is to establish an impedance spectrum quantitative validation technique to validate the whole experimental spectrum and to identify the individual points within a spectrum that do not comply any of the four conditions, in order to remove these inconsistent points from the analysis. The designed validation method consists in a Kramers Kronig (KK) validation test, by equivalent electrical circuit fitting, coupled with a Montecarlo error propagation method. In a first step, the experimental spectrum is fitted to a particular electrical equivalent circuit, which satisfies the KK relations. Then, in a second step, a statistical Montecarlo method is used in order to propagate the model fitting parameter uncertainty through the model. Using this approach, a consistency region is built for a given confidence level: the experimental points inside this region are considered consistent for the given confidence level, whereas the outside points are rejected. The method was used on PEMFC experimental impedance spectra; and it successfully managed to identify inconsistent points, associated to no stationarities.

Electrochemical Impedance Spectroscopy (EIS) is a widely used electrochemical measurement technique that has been used in a great spectrum of fields since it allows deconvolving the individual physic- chemical processes that take place in a given system. Ohm s generalized law, and thus the impedance concept, are only valid if 4 conditions are fulfilled: causality, finiteness, stationarity and linearity. In the case that any of these conditions is not achieved, the obtained impedance spectra will present distortions that may lead to biased or even erroneous results and conclusions. For this reason it is crucial to verify if the 4 conditions are fulfilled, before accepting the results extracted from impedance spectra. In this work, a linearity assessment quantitative method based in the total harmonic distortion (THD) parameter is presented and verified experimentally. The experimental validation of the implemented method showed that the implemented method is able to assess quantitatively the linearity of the system. In addition, it is also able to determine the threshold frequency above which the system will not present significant nonlinear effects even for large perturbation amplitudes. It was observed that the THD method is more sensitive to nonlinear effects than the spectra themselves.

[EN] The high electrode overpotentials for HER hinder the high scale hydrogen production by means of alkaline water electrolysis. In order to obtain cathodes with lower overpotentials, macroporous Ni-Co electrodeposits have been developed. The catalytic activity of these materials have been studied in KOH 30 wt.%., [ES] Los elevados sobrepotenciales de los electrodos para la REH dificultan la producción de hidrógeno a gran escala mediante la electrólisis alcalina del agua. Con la finalidad de obtener cátodos con menores sobrepotenciales se han desarrollados electrodepósitos porosos de Ni-Co y se ha estudiado su actividad catalítica para la HER en KOH (30% peso).

The performance of a cation-exchange membrane (CEM) used for recovering zinc from real spent pickling baths is studied in this work. These spent baths contain high amounts of ZnCl2 and FeCl2 in aqueous HCl media. The results obtained with this membrane are compared with those obtained with an anion-exchange membrane (AEM) treating the same effluent. The effect of the presence or absence of initial zinc in the cathodic compartment is also studied. The absence of initial zinc in the cathodic compartment in the CEM experiments permits iron codeposition. Furthermore, the results obtained with the CEM are worse than those obtained with the AEM for all the figures of merit. This fact shows the need of filling the cathodic compartment with a synthetic zinc solution. The presence of zinc in the cathodic compartment from the beginning of the electrolysis not only inhibits iron codeposition but also favors zinc deposition as the hydrogen evolution reaction becomes a secondary reaction, improving by this way the results of all the figures of merit of the reactor with the CEM. A deep study about the effect of the applied current and the concentration of the synthetic zinc solution placed in the cathodic compartment permits to reach the equilibrium between the zinc transferred through the membrane and that deposited on the cathode. Therefore, the synthetic cathodic zinc is not consumed at any time. Moreover, under this circumstances iron codeposition is also avoided.

Actualmente, el 43% de la producción mundial de zinc se destina al proceso de galvanizado por inmersión en caliente. Previamente a la introducción de las piezas en el baño de zinc fundido, éstas necesitan una serie de tratamientos superficiales. Entre estos tratamientos cabe destacar la etapa de decapado, que consiste en la inmersión de las piezas en un baño de ácido clorhídrico para eliminar de su superficie cáscaras y restos de óxido, como la etapa más contaminante del proceso de galvanizado, ya que los baños agotados de decapado contienen elevadas concentraciones de ZnCl2 y FeCl2 en HCl. En la presente Tesis Doctoral se realiza un estudio en profundidad de la recuparación electroquímica del zinc, presentándola como una alternativa limpia y eficaz en la que se pretende recuperar el componente de mayor valor añadido, en su estado metálico, que podría ser directamente reintroducido en el proceso de galvanizado de zinc por inmersión en caliente. Previamente al uso de la electrólisis como tratamiento de los baños agotados de decapado se realizó un estudio electroquímico de la disolución mediante la técnica de la voltametría cíclica. Este estudio determinó que el zinc se deposita en masa a partir de -1V, situándose su pico de reducción próximo a los -1.5V. Del análisis de las diferentes voltametrías cíclicas realizadas se dedujo que la deposición del zinc es un proceso irreversible, controlado tanto por la transferencia de materia como por la transferencia de carga, y transcurre mediante la formación de una película de hidróxidos de zinc sobre la superficie del electrodo gracias a aumentos locales del pH promovidos por la HER. También se determinó que el zinc y el hierro se depositan siguiendo un proceso de co-deposición anómala que permite que el zinc se deposite preferentemente al hierro sobre la superficie del electrodo, pues la película de Zn(OH)2 inhibe la deposición del hierro. No obstante, la estabilidad de la película de Zn(OH)2 depende, en gran medida, de la r

Proyecto confidencial (Riunet)

Consulta en la Biblioteca ETSI Industriales (5387), [ES] El objetivo del Proyecto Final de Carrera aquí presentado es el diseño y la optimización de Sistemas de Pilas de Combustible, para contribuir al desarrollo de esta tecnología que representa una propuesta doblemente beneficiosa en referencia a la seguridad energética y medioambiental. Con este propósito en mente, la parte fundamental del proyecto es el desarrollo de un modelo paramétrico que prediga el comportamiento de las pilas de combustible poliméricas, usando una combinación de técnicas de modelización empíricas y mecanísticas. Considerando propiedades de transporte de masa, potenciales de equilibrio termodinámico, resistencias internas y polarizaciones ohmicas y de activación, se definirá el voltaje de la pila de combustible individual, en función de variables de operación tales como la temperatura, la corriente y las presiones parciales de oxígeno e hidrógeno. Este estudio enfatizará posteriormente en optimizaciones de eficiencia y coste para las celdas individuales, los stacks y los sistemas de pilas de combustible, con el objetivo de determinar las condiciones de operación más favorables que conduzcan a los mejores rendimientos. Tanto el desarrollo del modelo como la realización de las optimizaciones se llevará a cabo en Mathcad 2001 Professional ya que es un software de cálculo extremadamente versátil y potente como lenguaje de programación, que permite de una forma sencilla un exhaustivo tratamiento de datos e implementación de modelos. Mediante la herramienta de Optimización que posee este software se determinarán las condiciones más favorables de funcionamiento de los sistemas de pilas de combustible. En el aspecto gráfico, las capacidades de edición y de representación en 2D y 3D del programa, harán posible la comprobación de la veracidad de los resultados obtenidos.

Proyecto Confidencial

[EN] The study of the hydrogen evolution reaction has been carried out in acid media at 25 ºC. This reaction has been studied by means of steady-state Polarization Curves and Electrochemical Impedance Spectroscopy. The optimal work range found was between 1.5 and 1.575 V, where the overpotential was low and the reaction was optimal., [ES] Se ha llevado a cabo el estudio sobre la evolución de la reacción de hidrógeno empleando electrodos de Pt/C, en medio ácido a 25 ºC. Esta reacción fue estudiada mediante Curvas de Polarización y Espectroscopía de Impedancia Electroquímica. El rango óptimo de trabajo fue entre 1.5 y 1.575 V, donde el sobrepotencial es bajo y la reacción era viable.

Consulta en la Biblioteca ETSI Industriales (5391), [ES] El objetivo de este Proyecto Final de Carrera es diseñar un controlador predictivo para un gasificador industrial, basado en el caso de la compañía Alstom. El gasificador utiliza carbón, vapor y aire como corrientes de entrada para producir un combustible gaseoso de bajo valor calorífico, mediante reacción entre compuestos hidrocarbonados. Este gas se denomina gas de sintesis y se emplea en procesos de combustión en turbinas de gas para generar energía eléctrica.

Consulta en la Biblioteca ETSI Industriales (5445), [ES] El presente proyecto tiene como objeto la realización de un modelo que describa el comportamiento de un gasificador de biomasa de lecho fluidizado, concretamente un gasificador de madera. Una vez desarrollado el modelo del gasificador, este se utilizará para estudiar el comportamiento dinámico del mismo.

Consulta en la Biblioteca ETSI Industriales (5991), [ES] El objeto del presente trabajo es estudiar la recuperación de cromo hexavalente procedente de los baños de mordentado de la industria de metalizado de plásticos. Todos los ensayos se han llevado a cabo durante el período de docencia e investigación del desarrollo de la tesis Doctoral orientada por el Dr D. Valentín Pérez Herranz. Tales ensayos han sido realizadas en el Laboratorio de Investigación nº 3, situado en el Departamento de Ingeniería Química y Nuclear de la Universidad Politécnica de Valencia.

Consulta en la Biblioteca ETSI Industriales (6088), [ES] El principal objetivo del presente Proyecto Final de Carrera es la puesta en práctica de una muestra representativa de conocimientos aprendidos en los largos años de trabajo que comprende la formación del Ingeniero Químico. Con la aprobación del conjunto de documentos que constituyen el Proyecto Final de Carrera, el autor del mismo obtiene el título de Ingeniero Químico. El propósito concreto del proyecto es la caracterización de una membrana de intercambio catiónico, para su aplicación en la recuperación del zinc presente en las aguas de enjuague de la industria del electrocincado, cuando dicha membrana permanece integrada en un sistema de electrodiálisis. Con esta finalidad se emplean diversas técnicas electroquímicas, tales como la cronopotenciometría, el método de Hittorf y el método de la fuerza electromotriz. El objetivo final es llegar a conocer los fenómenos de polarización de la membrana catiónica y, de este modo, discernir si la electrodiálisis es una técnica eficaz o no para recuperar el zinc de este tipo de efluente industrial. El proyecto se ha realizado íntegramente en el Departamento de Ingeniería Química y Nuclear de la Universidad Politécnica de Valencia, donde una de las ramas de investigación más desarrolladas es la de la electroquímica, en particular, los estudios electrodialíticos de recuperación de metales pesados. Por tanto, mediante este Proyecto Final de Carrera, se pretende aportar resultados de interés en este campo de investigación.

The increasing demand for clean industrial processes has intensified the use of electrodialysis in the treatment of metal containing effluents and encourages the investigation of the different phenomena involved in the transport of metal ions through cation-exchange membranes. Ion sorption, chronopotentiometric and current–voltage characteristics have been obtained to characterize the transport of sodium and iron through homogeneous and heterogeneous cation-exchange membranes. The heterogeneous membranes having a broader pore size distribution showed increased electrical resistances with solutions of trivalent iron, which may be caused by the blockage of the smallest pores by multivalent ions. However, for both types of membranes an unexpected decrease of the electrical resistance with increasing current densities was verified with concentrated solutions of Fe2(SO4)3. This behavior was explained to be a consequence of the dissociation of FeSO4+ ions into more conductive Fe3+ and SO42− ions as the depleting solution layer becomes diluted. When tested with multicomponent mixtures, the homogeneous perfluorosulfonic membranes show an increased preference for Na+ ions at low current densities and, once Na+ ions are depleted from the membrane surface Fe3+ ions are transported preferentially at higher current densities. On the contrary, both Na+ ions and Fe(III) species are responsible for the ion transport through the heterogeneous membranes within the ohmic regime of currents.

[EN] Open circuit losses encompass a set of phenomena that reduce PEM fuel cell (PEMFC) efficiency, especially at low current densities. Properly modelling these losses is crucial for obtaining PEMFC models that reproduce accurately the experimental behaviour of PEMFCs operating at low current densities. The open circuit losses can be disaggregated into three distinct contributions: mixed potential, hydrogen crossovers and internal short-circuits. The aim of this work is to obtain a model for the anodic and the cathodic pressure effects on the hydrogen crossovers and the internal short-circuits in a commercial PEMFC. In order to achieve this goal, the hydrogen crossovers and the internal short-circuit were measured experimentally on a commercial PEMFC by linear voltammetry. The measurements were performed at a given temperature and gas inlet humidification level, for different anodic and cathodic pressures.

In the present work the recovery of sulfuric acid from acid mine drainage by means of 3-compartment electrodialysis (ED) is evaluated. An effective recovery of sulfuric acid free from Fe(III) species was obtained in the anodic compartment as a result of the co-ion exclusion mechanism in the membranes. The difference in the pH and pSO42 − values between the membrane phase and the external electrolyte promotes the dissociation of complex species inside the membranes. This phenomenon impedes the transport of Fe(III) and sulfates in the form of complex ions toward the anodic and cathodic compartment, respectively. The current efficiency values of the anion-exchange membrane at different current densities were approximately constant with time. However, the increase in the recovery of acid decreases as the current increases. This result is explained by the shift in the equilibrium at the membrane/solution interface as more SO42 − ions cross the anionic membrane and, by the enhancement of the dissociation of water when the limiting current density is exceeded. The main limitation of the process is related to an abrupt increase in the cell voltage due to the formation of precipitates at the surface of the cation-exchange membrane.

The performance of a one (OCR) and a two-compartment electrochemical reactor in the presence of a cation-exchange membrane (CEM) for the zinc recovery present in the spent pickling baths is analyzed in this paper under galvanostatic control. These solutions, which mainly contain ZnCl2 and FeCl2 in aqueous HCl media, come from the hot dip galvanizing industry. The effect of the applied current, the dilution factor of the baths and the presence or absence of initial cathodic zinc is also studied. For the 1:50 diluted spent bath, OCR experiments initially present higher values of the figures of merit than those obtained in the presence of the CEM since zinc is close to the cathode from the first electrolysis instants. However, at long electrolysis times, OCR presents zinc redissolution for all the current values tested due to the chlorine and iron presence close to the zinc deposits. In addition, the iron codeposition phenomenon is also observed in the OCR experiments when pH values are close to 2. On the other hand, CEM experiments become very similar to the OCR experiments at long time values since the CEM under these experimental conditions prevents zinc redissolution phenomenon and also iron codeposition. When the 1:50 diluted bath is concentred to 1:10, OCR experiments present the same tendency as that observed for the 1:50 dilution factor but the effect of zinc redissolution is increased due to the greater amount of chlorine generated in the anode. Under these experimental conditions, iron deposition has also been observed in the presence of the cation-exchange membrane as the rate of zinc deposition is greater than that of zinc transport through the membrane, and the zinc/iron ratio in the cathodic compartment is not high enough to prevent iron codeposition. In both cases, the pH values when iron codeposits with zinc are close to 2 and the zinc/iron ratio is below 0.6. The presence of initial zinc in the cathodic compartment of the electrochemical reactor enhanc

Electrochemical Impedance Spectroscopy (EIS) is a suitable and powerful diagnostic testing method for fuel cells because it is non-destructive and provides useful information about fuel cell performance and its components. In this work, EIS measurements were carried out on a 300 W stack with 20 elementary cells. Electrochemical impedance spectra were recorded either on each cell or on the stack. Parameters of a Randles-like equivalent circuit were fitted to the experimental data. In order to improve the quality of the fit, the classical Randles cell was extended by changing the standard plane capacitor into a constant phase element (CPE). The effects of output current, cell position, operating temperature and humidification temperature on the impedance spectra were studied.

[EN] Alkaline water electrolysis is one of the easiest methods for hydrogen production, offering the advantage of simplicity. Moreover, it represents an environmentally friendly technology for production of high purity hydrogen. Nevertheless, the elevated production costs due to low conversion efficiency and electrical power expenses can be named as the main drawbacks of electrochemical hydrogen production. This work is focused on the development and characterization of 3D porous Ni cathodes for alkaline electrolyzers. The electrodes were synthesized by nickel electrodeposition on copper foams obtained from hydrogen bubbles dynamic templates (double-template electrochemical process). The developed electrodes were characterized by SEM, confocal laser scanning microscopy, and EDX. The electrocatalytic performance of the developed electrodes for hydrogen evolution reaction (HER) was evaluated in 30 wt.% KOH solution by using hydrogen discharge curves and galvanostatic tests. Results show that the use of the developed electrodes as cathodes in electrolysis systems makes possible an energy saving of ca. 25% in conditions at which industrial alkaline water electrolysis is carried out, in comparison with the smooth commercial Ni electrodes.

The optimum temperature for fixing zirconium phosphate, obtained by precipitation, on a low-cost ceramic support was determined in order to obtain an inorganic cation exchange membrane for electrodialysis. Zirconium phosphate ion exchange capacity maximised between 450 and 550°C, thus it was considered the optimum processing temperature. The origin of this maximum was investigated by means of X-ray diffraction and termogravimetry and evolved gas analysis. Zirconium phosphate formation by precipitation in the porous network of the support was verified by scanning electron microscopy and energy dispersive X-ray analysis and mercury intrusion porosimetry. The membrane obtained after thermal treatment at 450°C displayed selectivity to the cations present in the spent rinse water of the chromium plating process. This property allows the recovery of chromium by removing the cations through the cation exchange ceramic membrane.

In this article, the innovative cation-exchange membranes obtained from ceramic materials are presented. Different microporous ceramic supports were obtained from an initial mixture of alumina and kaolin, to which a varying content of starch was added in order to obtain supports with different pore size distributions. The deposition of zirconium phosphate into the porous supports generates membranes with cation-exchange properties. The fabrication of ion-exchange membranes which could resist aggressive electrolytes such as strong oxidizing spent chromium plating baths or radioactive solutions would allow the application of electrodialysis for the decontamination and regeneration of these industrial effluents. The performance of the manufactured membranes was studied in nickel sulfate solutions by means of chronopotentiometry. An increase of the membrane voltage drop during chronopotentiometric measurements was observed in some membranes, which seems to be a consequence of concentration polarization phenomena resulting from the ionic transfer occurred through the membranes. Current voltage curves were obtained for the different ceramic membranes, allowing the calculation of their ohmic resistance. The ohmic resistance of the membranes increased when the open porosity (OP) of the samples was incremented up to a value of 50%. For values of OP higher than 50%, the resistance of the membranes decreased significantly with porosity.

In this work, macroporous Ni, Co and NieCo electrodes have been developed by codeposition at high current density on stainless steel (AISI 304) substrates. The obtained materials were characterized both morphologically and chemically by confocal laser scanning microscopy, and SEM coupled with EDX analysis. The activity for hydrogen evolution reaction (HER) on the obtained layers was assessed by using pseudo-steady-state polarization curves and electrochemical impedance spectroscopy (EIS) in alkaline solution (30 wt.% KOH). The electrochemical results show that HER on these electrodes takes place by the VolmereHeyrovsky mechanism. The synthesized coatings present higher catalytic activity for HER than commercial smooth Ni electrode. As the Co content increases in the electrodeposition bath the obtained structures show lower surface roughness factors. Ni eCo deposit with a Co content of 43 at.% manifests the highest intrinsic activity for HER as a consequence of the synergetic combination of Ni and Co.