Monitorización del estado de carga de una batería de flujo redox todo vanadio mediante observador de modo deslizante

El almacenamiento de energía por medio de baterías de flujo redox es un concepto relativamente nuevo. Estas baterías permitirían el almacenamiento de energía a gran escala y poseerían una gran durabilidad. Un problema al que se enfrentan es la obtención del estado de carga (SOC, por las siglas de la expresión inglesa “state of charge”), debido a que ciertos factores producen una degradación que dificulta su medición.A lo largo del tiempo se han desarrollado diferentes métodos de medición del SOC. Este proyecto implementará un sistema de estimación mediante observador deslizante. El cual compara los valores modelados con los medidos y otorga una estimación de las variables no observables.El modelo se basa en el descrito en la referencia “Sliding Mode Observer and Dynamic Model Including Capacity Fading Factor” desarrollado por Binyu Xiong y colaboradores. El modelo de degradación por su parte, se implementará basándose en datos simulados.<br /

Synthesis and stability of Pt3Co and Pt0.7≤X≤1Co films voltammetrically activated in acidic medium for methanol fuel cell application

Pt-Co thin films have been prepared by means of electrodeposition method, due to the interest of this alloy as catalyst in acid fuel cells. As the stability of the catalyst is fundamental to consider its applicability, the behavior of the films as a function of the composition during voltammetry activation in acidic medium has been studied. The Pt3Co films show high stability, maintaining their morphology, X-ray diffraction profile, composition and high surface area, and show good catalytic behaviour for methanol electro-oxidation in acidic medium. However, the Pt0.7≤x≤1Co films present low stability and evolve during the test to flatter films of lower effective area and Pt3Co stoichiometry, by losing cobalt. Only Pt-Co electrodeposited films of defined compositions show the enough stability and properties to be used as good materials for electro-oxidation processes in acidic media

Diseño hidráulico de una instalación para una batería de flujo redox

El agravamiento de la crisis medioambiental, climática y de recursos que tiene lugaren la actualidad ha hecho patente la necesidad de un cambio en el modelo deproducción de energía global, cambiando las fuentes fósiles por otras renovables. Paracompensar la intermitencia de éstas, surgen nuevos sistemas de almacenamiento deenergía y, de entre todos ellos, unos de los más atractivos dadas sus ventajas son lasbaterías de flujo redox.Este proyecto presenta el diseño de una instalación para una batería de flujo redoxde 5 kW de potencia y 10 kW·h de capacidad. Para conseguir estas especificaciones,es necesario bombear dos fluidos desde sendos depósitos hacia la batería. Lacomposición de estos fluidos, el volumen y el caudal son los que condicionan la potenciay la capacidad del sistema electroquímico, por lo que el primer paso de este trabajo esdeterminar estos parámetros. Con los parámetros de la batería se definen los requisitosque deben cumplir tanto la estación de bombeo (diámetros, materiales que se puedenemplear, etc.) como la estructura metálica donde se dispone la instalación.También se desarrollan distintos cálculos hidráulicos para seleccionar todos loselementos comerciales que componen la instalación (instrumentación, bombas,depósitos…) y garantizar su correcto funcionamiento en cuanto a caudales y pérdidasde presión. Así mismo, se ha elaborado un presupuesto detallado de los distintoscomponentes y se ha realizado un análisis de las medidas de seguridad y salud que sedeben adoptar tanto para el personal como para la propia instalación.En el trabajo, además, se detallan los resultados experimentales obtenidos de unabatería de menor tamaño, analizando las medidas de pérdida de presión en un electrodoporoso de fieltro de carbono, los ciclos de carga/descarga de la batería y la generaciónde electrolitos.El desarrollo de este proyecto ha tenido lugar en el Laboratorio de Investigación enFluidodinámica y Tecnologías de la Combustión (LIFTEC), donde se pretende construirla instalación diseñada, y posteriormente evaluar la operación de la batería de flujoredox.<br /

Electrocatalytic oxidation of methanol on CoNi electrodeposited materials

Cobalt-nickel bimetallic materials electrodeposited on Si/Ti/Ni substrates were evaluated for the oxidation of methanol in alkaline media. CoNi samples were prepared potentiostatically selecting conditions adequate to achieve the desired Co/Ni ratio. All samples were characterized by X-ray fluorescence and cyclic voltammetry to determine their composition and electrochemical behaviour. The electrocatalytical performance of prepared samples was evaluated also by cyclic voltammetry using methanol solutions in alkaline media. Material composition, methanol and NaOH concentration, and temperature were the variables studied. The results indicate that a cobalt excess inhibits the methanol oxidation. In the same way, a significant enhancement of the oxidation current was observed on increasing the NaOH concentration up to 0.5 M, but for higher concentrations the electrocatalytic performance of these materials decreases. With regard to the increase of MeOH concentration or temperature, both variables are related to an improvement of the electrocatalytic performance. Finally, the effect of platinum skin on the CoNi deposits was evaluated, concluding that it favours MeOH oxidation but does not protect the substrate surface from the damage exerted by excessive NaOH concentration

Effective new method for synthesizing Pt and CoPt3 mesoporous nanorods. New catalysts for ethanol electro-oxidation in alkaline medium

In this work, an electrochemical methodology consisting of electrodeposition in ionic liquid-in water (IL/W) microemulsions has been revealed as an excellent pathway to prepare highly mesoporous nanorods with pore sizes of a few nanometers, with a significant growth rate. The nanochannels of a polycarbonate membrane (hard template) define the diameter of the nanorods, the deposited charge controls its length and the mesoporous structure replicates the structure of the microemulsion (soft template). This procedure has been used to prepare mesoporous nanorods of pure metal (Pt) or of alloy (CoPt3) with very high electrochemically active surface area (228 and 235 m2 g-1, respectively), as a consequence of the accessible three-dimensional interconnected network formed by the mesopores. When the synthesised mesoporous nanorods were tested as catalysts for ethanol electrooxidation in alkaline medium, excellent catalytic performance was found, with significant improvements over the performance of compact nanorods or commercial PtRu nanoparticles. The oxidation current / mass ratio of the mesoporous nanorod catalyst is significantly higher and, moreover, the onset potential of the ethanol oxidation is clearly advanced. Mesoporous CoPt3 nanorods show similar performance with pure platinum mesoporous nanorods and good stability in the alkaline medium, which makes them very good candidates as catalysts of the anodic reaction in direct ethanol fuel cells, with greater economy with respect to pure Pt catalysts

Diseño e integración del sistema de monitorización y control en la instalación experimental de una batería de flujo redox

Dada la crisis medioambiental de hoy en día es necesario apostar por las fuentes renovables de energía. La producción de electricidad mediante energías renovables es intermitente, es decir, tiene picos y valles de producción a lo largo del día ya que dependerá de las condiciones climáticas. Por este motivo, surge la necesidad de desarrollar nuevos sistemas de almacenamiento de energía para poder satisfacer la demanda a lo largo del día. Uno de los sistemas más prometedores de almacenamiento de energía son las baterías de flujo redox. En este trabajo se va a diseñar y fabricar un sistema de monitorización a tiempo real y manejo de las bombas hidráulicas de la instalación de una batería de flujo redox de 1 kW de potencia. Para ello será necesario elegir unos sensores de presión, temperatura y caudal que se adapten a las características de la instalación y del electrolito, que es un ambiente potencialmente corrosivo. Además de la elección de los sensores será necesario montar un circuito de adaptación de la señal entre los sensores y la tarjeta de adquisición de datos NI USB 6008. Por otra parte, se programarán los variadores de frecuencia que comandan las bombas hidráulicas para poder manejarlos desde la misma tarjeta de adquisición de datos. A su vez, será necesario desarrollar un programa en LabVIEW con una interfaz que permita ver estas variables a tiempo real y sea posible actuar sobre la velocidad de rotación de los motores eléctricos de las bombas hidráulicas. También se analizarán los resultados de las primeras puestas en marcha hasta la elaboración de esta memoria y las conclusiones que se han podido obtener. Este proyecto se ha desarrollado en el Laboratorio de Investigación en Fluidodinámica y Tecnologías de la Combustión (LIFTEC). Con este proyecto se espera analizar el comportamiento del stack de 1 kW y servirá como base a futuros proyectos de investigación sobre estas baterías. <br /

Electrocatalytic oxidation of methanol on CoNi electrodeposited materials

Cobalt-nickel bimetallic materials electrodeposited on Si/Ti/Ni substrates were evaluated for the oxidation of methanol in alkaline media. CoNi samples were prepared potentiostatically selecting conditions adequate to achieve the desired Co/Ni ratio. All samples were characterized by X-ray fluorescence and cyclic voltammetry to determine their composition and electrochemical behaviour. The electrocatalytical performance of prepared samples was evaluated also by cyclic voltammetry using methanol solutions in alkaline media. Material composition, methanol and NaOH concentration, and temperature were the variables studied. The results indicate that a cobalt excess inhibits the methanol oxidation. In the same way, a significant enhancement of the oxidation current was observed on increasing the NaOH concentration up to 0.5 M, but for higher concentrations the electrocatalytic performance of these materials decreases. With regard to the increase of MeOH concentration or temperature, both variables are related to an improvement of the electrocatalytic performance. Finally, the effect of platinum skin on the CoNi deposits was evaluated, concluding that it favours MeOH oxidation but does not protect the substrate surface from the damage exerted by excessive NaOH concentration

Effective new method for synthesizing Pt and CoPt3 mesoporous nanorods. New catalysts for ethanol electro-oxidation in alkaline medium

In this work, an electrochemical methodology consisting of electrodeposition in ionic liquid-in water (IL/W) microemulsions has been revealed as an excellent pathway to prepare highly mesoporous nanorods with pore sizes of a few nanometers, with a significant growth rate. The nanochannels of a polycarbonate membrane (hard template) define the diameter of the nanorods, the deposited charge controls its length and the mesoporous structure replicates the structure of the microemulsion (soft template). This procedure has been used to prepare mesoporous nanorods of pure metal (Pt) or of alloy (CoPt3) with very high electrochemically active surface area (228 and 235 m2 g-1, respectively), as a consequence of the accessible three-dimensional interconnected network formed by the mesopores. When the synthesised mesoporous nanorods were tested as catalysts for ethanol electrooxidation in alkaline medium, excellent catalytic performance was found, with significant improvements over the performance of compact nanorods or commercial PtRu nanoparticles. The oxidation current / mass ratio of the mesoporous nanorod catalyst is significantly higher and, moreover, the onset potential of the ethanol oxidation is clearly advanced. Mesoporous CoPt3 nanorods show similar performance with pure platinum mesoporous nanorods and good stability in the alkaline medium, which makes them very good candidates as catalysts of the anodic reaction in direct ethanol fuel cells, with greater economy with respect to pure Pt catalysts

Electrochemical synthesis of mesoporous CoPt nanowires for methanol oxidation

A new electrochemical method to synthesize mesoporous nanowires of alloys has been developed. Electrochemical deposition in ionic liquid-in-water (IL/W) microemulsion has been successful to grow mesoporous CoPt nanowires in the interior of polycarbonate membranes. The viscosity of the medium was high, but it did not avoid the entrance of the microemulsion in the interior of the membrane"s channels. The structure of the IL/W microemulsions, with droplets of ionic liquid (4 nm average diameter) dispersed in CoPt aqueous solution, defined the structure of the nanowires, with pores of a few nanometers, because CoPt alloy deposited only from the aqueous component of the microemulsion. The electrodeposition in IL/W microemulsion allows obtaining mesoporous structures in which the small pores must correspond to the size of the droplets of the electrolytic aqueous component of the microemulsion. The IL main phase is like a template for the confined electrodeposition. The comparison of the electrocatalytic behaviours towards methanol oxidation of mesoporous and compact CoPt nanowires of the same composition, demonstrated the porosity of the material. For the same material mass, the CoPt mesoporous nanowires present a surface area 16 times greater than compact ones, and comparable to that observed for commercial carbon-supported platinum nanoparticles

Vanadium redox flow battery state of charge estimation using a concentration model and a sliding mode observer

Vanadium redox flow batteries are very promising technologies for large-scale, inter-seasonal energy storage. Tuning models from experimental data and estimating the state of charge is an important challenge for this type of devices. This work proposes a non-linear lumped parameter concentration model to describe the state of charge that differentiates the species concentrations in the different system components and allows to compute the effect of the most relevant over-potentials. Additionally, a scheme, based on the particle swarm global optimization methodology, to tune the model taking into account real experiments is proposed and validated. Finally, a novel state of charge estimation algorithm is proposed and validated. This algorithm uses a simplified version of previous models and a sliding mode control feedback law. All developments are analytically formulated and formally validated. Additionally, they have been experimentally validated in a home-made single vanadium redox flow battery cell. Proposed methods offer a constructive methodology to improve previous results in this field.Peer ReviewedPostprint (published version