Investigation of fluorite and perovskite materials for energy applications

Abstract

Reducing the carbon footprint of the actual energy supply system is of vital importance so as to address the issue of climate change. Thus, the development of energy conversion & storage technologies, tackling the electricity’s intermittency of the renewables source technologies, is of great interest. Solid oxide fuel cells (SOFCs) possess valuable advantages compared to the other energy storage & conversion devices, such as its long-term durability, high values of conductivities or its utilization with various types of gases. However, issues still exist on the hydrogen electrode. Therefore, the development of alternative hydrogen electrodes represents a challenge as it needs to meet several requirements, such as good ionic and electronic conductivities, redox stability or being single-phase.

Copper doped ceria (CCO) is considered as a promising candidate. This work focused on solving some issues inherent to this material. The challenge of synthesizing a single-phase solid-solution of CCO has been resolved and synthesis’ parameters influences were investigated. Cu solubility has been determined and equals to 10%mol for the solid-solutions. The absence of consensus concerning the oxidation states of the cations has also been inquired. In both surface and bulk, Cu +2 is declared as the main oxidation state of Cu. However, the presence of Cu +1 is assured. This confirms the significant concentration of Ce +3 detected in CCO, counter-balancing the charge imbalance due to the creation of oxygen vacancies. In addition to the obtaining of the phase diagram of copper doped ceria, preliminary results on the application of exsolution of nanoparticles on CCO fluorites were obtained and Cu enriched nanoparticles were generated on the surface.

Ru-doped strontium yttrium titanate (SYTRu) was also investigated as alternative anode material. In this work, the main issue of this material refers to the incorporation of Ru into the perovskite lattice. Evidences concerning the real substitution of Ti by Ru were obtained by X-ray absorption spectroscopy (XAS). Furthermore, reduced samples showed Ru nanoparticles on their surface.