Studio di materiali avanzati per celle a combustibile ad ossidi solidi: influenza dei droganti e delle tecniche di sintesi sulle proprietà di anodi ed elettroliti

摘要

Today fuel cell (FC) technology is envisaged as a strategic alternative for providing clean energy through the exploitation of renewable sources; FC research is substantially funded by governments as a mean to meet the global market demand of zero environmental impact. Due to the high level of efficiency, FC devices are already able to compete with the existing power generation technologies and, in particular, solid oxide fuel cells (SOFCs) plants for stationary application constitute one the most efficient way to produce electric power and heat. Nowadays, the main challenges for SOFC research activity are: i) improving costs and durability, by reducing the operating temperature from ∼1000°C (HT) to ~500-800°C (IT); and ii) using renewable fuels such as hydrogen and biofuels obtained by industrial and municipal wastes or energy crops. To achieve these purposes, it is essential to seek new materials characterized by suitable ionic conductivity for electrolytes and high electrocatalytic activity for electrodes. The electrolyte material must ensure high ionic conductivity, low electronic conductivity and very low permeability to both fuel and air in the operative temperature range. On the other hand, the anode material must be a mixed ionic-electronic conductor in the same temperature range, an efficient oxidation electrocatalyst and, finally, ensure good chemical and structural compatibility with the electrolyte. udIn this light, the present study focuses on exploring electrolyte and anode materials for IT-SOFCs fuelled with H2 and, as a reference for carbonaceous streams, with CH4. udElectrolyte materials based on CeO2 doped with samarium or gadolinium are the most promising ion oxide (O2-) conductors in the intermediate range. The research activity concerning these compounds is mainly addressed to achieve the best performances in dependence of the doping amount and preparation routes. In this thesis the study of doped-CeO2 has been divided in two different parts. In the former part, the influence of different preparation routes on the ionic conductivity of Ce0.8Sm0.2O2-x has been evaluated. In the latter, a detailed investigation on local structure in Er-, Yb- and Sm-doped ceria has been carried out, aiming at elucidating the role of different dopants on the mechanism of ionic conduction.udConcerning the anode materials, the issues of resistance towards poisoning originated by “dirty” fuels and compatibility with the electrolyte focused the research activity on the development of new oxide materials alternative to cermets. Among other candidates, it has been recently observed that La1-xSrxCr1-yFeyO3-δ has suitable properties as potential anode for IT-SOFCs. In this thesis LaCrO3-based anode materials have been investigated relative to the issues of optimal composition, structure, mixed ionic-electronic conductivity, catalytic activity towards fuel oxidation, also with consideration for the aspect of resistance to poisoning by carbonaceous fuel.