Advanced Energy Materials and Research

Biography

Biography: Olivier Joubert

Abstract

The research on solid oxide fuel cell (H⁺ or O^2- SOFC) is based on both the synthesis of new materials and the design process of the cell. The main advantage of SOFC is that they can work under hydrocarbon fuel at temperature higher than ≈700°C. In the current SOFC systems, the most widely used electrolyte is yttria-stabilized zirconia (YSZ) which is inexpensive and shows an acceptable conductivity level. But YSZ is very refractory and its major drawback is its reactivity during the sintering process with lanthanum- and strontium-based cathode materials, which leads to the formation of an insulating layer such as SrZrO₃ or La₂Zr₂O₇. There is also a great interest to find ceramic based fuel cells, for mobile application, working at low temperature (≈400°C). This can be achieved in H⁺-SOFC with a ceramic membrane showing a good proton conductivity level. The state of the art perovskite type yttrium-doped BaCeO₃ (called BCY) shows a proton conductivity level above 1 mS/cm at 400°C. But due to its high basicity, BCY tends to decompose, in this temperature domain, in air containing CO₂. Finding new electrolyte material is one of the issues. In this presentation, after a briefly state-of-the art concerning SOFC electrolyte, we will report on high-temperature proton and oxide ion conductivities in two new class of oxyborates, La₂₆O₂₇(BO₃)₈ and doped Ba₃Ti₃O₆(BO₃)₂ compounds. Both samples were prepared by solid-state reaction and characterized using x-ray diffraction and electrochemical impedance spectroscopy. Quite high conductivity level, about 6.8×10^–4 and 1.5×10^–4 S/cm at 700°C in air were observed respectively. The transport properties can be understood in terms of the presence in high concentrations of oxygen and barium vacancies as well as oxygen interstitials as observed in hybrid density-functional defect calculations.