DESIGN, REALIZATION AND CHARACTERIZATION OF INNOVATIVE ANODE MATERIALS FOR LOW AND INTERMEDIATE TEMPERATURE DIRECT METHANE SOLID OXIDE FUEL CELLS

The Solid Oxide Cells (SOFC) are high temperature electrochemical devices able to convert with high efficiency the chemical energy of a fuel into electric energy and reverse. Ni/YSZ is the state of art electrode material, while hydrogen is the mainly used fuel in the nowadays commercial devices. The usage of green hydrogen must be the main goal of our research in the energetic field. Anyway, it is unrealistic to think that in a very short time our cities can be ready to use hydrogen as main fuel. A possible compromise could be the usage of biogas, that can be produced in a green way from the biowaste of our agriculture activities. Since the main component of biogas is methane, in this work, the possibility to implement methane fueled Solid Oxide Fuel Cells in our cities is investigated. The main problem to achieve this result is to identify a new anodic material that can replace the state of art Ni based cermet. Indeed, Ni strongly catalyze carbon coking and this lead in a short application time to the surface poisoning. In addition, is consolidated the knowledge about the mechanical breakage of Ni/YSZ when exposed to carbon containing molecules. Therefore, new Ni free anode materials will be discussed in this work. The choice of the candidate material was made trying to transform a handicap to an opportunity. If we must avoid the state of art anode material, why not try to use a compound that is possible to use both as anode and both as cathode? In this way, the productive costs can be considerably lowered. Otherwise, why not try to lower the working temperatures of this technology with the consequent lowering of the operative costs? Before the show up of the proposed materials and their results, a general introduction to the technology and its challenge is given. Different composition and Cu doped formulation of La1-xSrxMnO3 (LSM), state of art cathode material, were synthetized and characterized. The effective realization of the desired compound is confirmed by X-Ray Diffractometry (XRD), while the morphology of the powders is observed by Scanning electronic Microscopy (SEM). The surface chemical composition is studied by X-Ray Photoelectron Spectroscopy (XPS), while the surface area of all the samples is calculated by BET analysis performed on N2 Adsorption-desorption isotherm. One of the most important goals of this work is the confirmation of the LSM stability in reductive atmospheres (H2 and CH4), that was confirmed by XRD after Temperature Programmed Reduction (H2-TPR) and the catalytic tests. In fact, the catalytic properties of this material towards methane oxidation were studied through a Gas Chromatographer (GC) and, finally, the electrochemical activity through Electronic Impedance Spectroscopy (EIS). Must be mentioned the attempt to increase the performances by changing the morphology. For this reason, LSM nanofibers, synthetized by Prof. Costamagna’s research group from University of Genova, were characterized and compared with LSM powders. To lower the working temperature to about 500 °C, another solution was investigated. In this case avoiding noble metal does not give satisfactory results from an applicative point of view. What we can do is to limit the quantity of noble metals and trying to enhance their properties by downsizing the dimension of the metal catalysts to a nanoscale. The creation of nanoparticles can significantly improve the catalytic performances through the creation of new crystalline planes. A Cu/GDC cermet with Pd nanoparticle infiltration was investigated. These two different solutions that can be effective for two different tasks, must have a common requirement: avoiding the carbon deposition on the electrode surface. For this reason, quantitative and qualitative analyses of the carbon deposition was studied by Raman Operando Spectroscopy performed at Danmarks Tekniske Universitet (DTU) under the supervision of Prof. Peter Holtappels.