Biomass-derived carbon materials for energy storage applications

Energy storage systems are an essential link in the implementation of renewable energies and in the development of electric vehicles, which are needed to reduce our dependence on fossil fuels and the emission of greenhouse gases. Various technologies have been proposed for energy storage based on different working principles, including lithium-ion batteries, emerging sodium-ion batteries and electric-double layer capacitors. Besides the quest for improving key aspects such as energy and power densities, current research efforts are devoted to foster the manufacturing of more environmentally friendly devices using sustainable materials. Carbon-based electrodes hold considerable promise in such terms due to their low cost, tailorable morphology and microstructure, and the possibility of processing them by direct carbonization of eco-friendly and naturally-available biomass resources. The main goal of this thesis is to develop carbon materials from biomass resources and study their applications as electrode for lithium-ion batteries, sodium-ion batteries and electric-double layer capacitors. En route towards that goal, it also aims at expanding our understanding of the microstructural changes of biomass-derived carbons with varying processing conditions and their effect on the electrochemical performance for each of these technologies. The first part of this work reports on the synthesis of graphitized carbon materials from biomass resources by means of an Fe catalyst, and the study of their electrochemical performance as anode materials for lithium-ion batteries (LIBs). Peak carbonization temperatures between 850 °C and 2000 ºC were covered to study the effect of crystallinity, surface and microstructural parameters on the anodic behavior, focusing on the first-cycle Coulombic efficiency, reversible specific capacity and rate performance. Reversible capacities of Fe-catalyzed biomass-derived carbons were compared to non-catalyzed hard carbon and soft carbons materials heated up to 2800 ºC. Moreover, in-situ characterization experiments were carried out to advance our understanding of the mechanisms responsible for catalytic graphitization. The second part of this work reports a comprehensive study on the structural evolution of hard carbons from biomass resources as a function of carbonization temperature (800 - 2000 ºC), and its correlation with electrochemical properties as anode materials for sodium-ion batteries (SIBs). Synchrotron X-ray total scattering experiments were performed and the associated atomic pair distribution function (PDF) extracted from the data to access quantitative information on local atomic arrangement in these amorphous materials at the nanoscale, as well as its evolution with increasing processing temperature. Then, electrochemical properties and the storage mechanisms involved on Na ions insertion into hard carbon structures at each characteristic potential regions were elucidated and correlated with microstructural properties. Finally, the third part of this work reports on the synthesis of nanostructured porous graphene-like materials from biomass resources using an explosion-assisted activation strategy by nitrate compounds and Ni as a graphitization catalyst. The thermal behavior during carbonization as well as the resulting microstructural and surface properties were evaluated at two different processing temperatures, 300 and 1000 ºC. Finally, their application as electrode materials for electric-double layer capacitors (EDLCs) and LIBs is investigated, with a view to their performance under high charge/discharge specific current densities experiments.Premio Extraordinario de Doctorado U

Uso de software de gestión de concursos de programación para evaluación continua

La implantación del EEES ha supuesto la entrada de la evaluación continua, que exige un seguimiento cuidadoso de la evolución del aprendizaje de los alumnos. Esto supone un esfuerzo extra por parte del profesorado, tanto por la necesidad de preparar las actividades como por su corrección. En este artículo describimos la experiencia de utilizar software de gestión de concursos de programación para automatizar la evaluación de los alumnos en la asignatura Estructura de Datos y Algoritmos, y extraemos algunas conclusiones interesantes que van más allá de la propia asignatura.SUMMARY -- The introduction of the European Higher Education Area led to the apparition of the continuous assesment, forcing teachers on thorough monitoring students. This imposes an extra task into our already full workload that involves not only the creation of new activities, but also their assesment itself. The paper presents our experience using pre-existing software designed to be used in programming contests. It took place while teaching a subject about data structures and algorithms. Moreover, the paper draws some interesting conclusions that are beyond the subject itself

Porous Graphene-like Carbon from Fast Catalytic Decomposition of Biomass for Energy Storage Applications

A novel carbon material made of porous graphene-like nanosheets was synthesized from biomass resources by a simple catalytic graphitization process using nickel as a catalyst for applications in electrodes for energy storage devices. A recycled fiberboard precursor was impregnated with saturated nickel nitrate followed by high-temperature pyrolysis. The highly exothermic combustion of in situ formed nitrocellulose produces the expansion of the cellulose fibers and the reorganization of the carbon structure into a three-dimensional (3D) porous assembly of thin carbon nanosheets. After acid washing, nickel particles are fully removed, leaving nanosized holes in the wrinkled graphene-like sheets. These nanoholes confer the resulting carbon material with ≈75% capacitance retention, when applied as a supercapacitor electrode in aqueous media at a specific current of 100 A·g–1 compared to the capacitance reached at 20 mA·g–1, and ≈35% capacity retention, when applied as a negative electrode for lithium-ion battery cells at a specific current of 3720 mA·g–1 compared to the specific capacity at 37.2 mA·g–1. These findings suggest a novel way for synthesizing 3D nanocarbon networks from a cellulosic precursor requiring low temperatures and being amenable to large-scale production while using a sustainable starting precursor such as recycled fiberwood.Spanish Government Agency Ministerio de Economí a y Competitividad (MINECO) (grant number MAT2016-76526-R)

Análisis regional del uso de las TIC por los hogares españoles

El propósito de este trabajo es analizar el uso de las TIC y el comportamiento de los hogares con respecto a las TIC. Para ello se analizan una serie de aspectos tales como digitalización de los hogares, alfabetización digital, e-Administración y políticas públicas del sector, que ayudan a comprender la implantación de las tecnologías de la información y la comunicación en los hogares españoles. En una segunda parte se analizan el equipamiento TIC que poseen los hogares, el uso que le dan a esos equipamientos (conexión a Internet, comercio electrónico, relación con las Administraciones Públicas….) y la evolución temporal de dichas variables, analizando además el posible efecto de la crisis en las variables estudiadas.Departamento de Economía AplicadaGrado en Administración y Dirección de Empresa

Estudio comparativo entre los combustibles tradicionales y las nuevas tecnologías energéticas para la propulsión de vehículos destinados al transporte

En el presente proyecto se recogen una serie de propiedades y características sobre los combustibles tradicionales derivados del petróleo, gasolina y gasoil, y sobre los combustibles alternativos que tienen posibilidades de sustituirlos o complementarlos en el futuro. Los datos recogidos se centran básicamente en particularidades interesantes para la aplicación de estos combustibles en motores alternativos de combustión interna de aplicación en automóviles. En primer lugar se describe cada uno de los combustibles seleccionados por separado y a continuación se concluye con un análisis comparativo de sus propiedades entre los mismos. Los resultados obtenidos se resumen en unas tablas que describen la posible aplicabilidad de los combustibles alternativos en el sector transporte. El trabajo pretende facilitar la toma de decisión técnica en cuanto a las posibles utilizaciones de los nuevos combustibles o sus combinaciones, en aplicaciones concretas