Defect-mediated charge and mass transport in energy materials

Conventional solid-oxide fuel cells (SOFCs) based on yttria-stabilized zirconia (YSZ) electrolytes and Ni-YSZ cermet anodes suffer performance degradation due to problems associated with the Ni-based anodes such as redox cycling instability, nickel agglomeration, carbon deposition, and sulfur poisoning. It is thus necessary to search for new, Ni-free materials that may hold potential for overcoming these problems. Recently, Ba₃Ti₃O₆(BO₃)₂ has been identified as a possible candidate for SOFC anodes or anode composites [1]. The oxyborate material undergoes a change from ionic under oxidizing and soft reducing conditions to mainly electronic transport under an extreme reducing atmosphere typical of anode environment, leading to a drastic enhancement in the electrical conductivity. In this talk, we introduce a theoretical framework, based on defect physics, to understand changes in the electrical transport mechanism caused by changes in the environment and to explore and design new materials for SOFC applications. [1] Doux et al., ACS Appl. Energy Mater. 1, 510 (2018).