Advanced Ceramics for Sustainable Energy Conversion Processes: from High Functionality Chemical Tailoring to Nanoscale Designed Materials

The last decades have been characterized by a constant increase in the need of energy coupled with an increase in the greenhouse gases emissions, since a large amount of the energy is provided by combustion plants burning fossil fuels. The level of CO2 has reached a negative record and this tendency has to be reversed in favor of a more environmentally sustainable approach. In this scenario different solutions for energy conversion and storage need to be found: the use of fossil fuels has to be reduced and replace with other and more sustainable forms of energy conversion. At the same time the change has to be guided by an improvement in the current technology for energy conversion to facilitate the transition process. For this purpose, the traditional combustion process can be improved using oxy-fuel conditions, where a stream of pure O2 provided by an oxygen transport membrane is used instead of air and the resulting high concentrated CO2 flue gas is easier to capture. A cleaner form of energy can be obtained using Solid Oxide Reversible Cells (SORCs), highly efficient electrochemical devices able convert chemicals directly into electrical current without production of pollutants. When operated in electrolysis mode, SORCs allow to store electrical energy in the form of fuels, obtained from CO2 reduction. Despite being extremely appealing, both these possibilities are not integrated in large scale energy plants yet, due mainly to their cost and long-term stability issues. These aspects can be improved with materials having a better performance and this can be achieved by an appropriate tailoring of their properties. This thesis presents the attempt to address these issues by developing novel advanced ceramic materials with high performances in order to fulfill a lower temperature application. In particular, this has been pursued aiming at improving the ionic conductivity of the materials. A GDC/YSZ nanocomposite has been prepared by inkjet printing and characterized as electrolyte, with attention to the interaction between the two phases. Complex perovskites have been designed and optimized to stabilize a high oxygen defective crystal phase displaying mixed ionic and electronic conductivity. These materials have been characterized in their structure, oxygen mobility and conductivity, before being tested as oxygen transport membranes and cathodes for solid oxide fuel cells.