Investigation of Alternative Mixed-Conducting Oxides for SOFC Anode Applications

Wednesday, 31 May 2017: 14:20
Churchill B2 (Hilton New Orleans Riverside)
E. M. Sabolsky (U.S. DOE, National Energy Technology Laboratory), X. Liu, J. W. Zondlo, H. Qi, T. Thomas (West Virginia University), R. Hart, and E. Jezek (GE Global Research)
The solid-oxide fuel cells (SOFCs) may undergo unwanted redox cycles during application and this may cause dimensional instability for the anode electrode. The state-of-the-art Ni/YSZ anode experiences a linear expansion of up to 1% when oxidized causing an irreversible microstructural change. Researchers are focusing on the development of many new SOFC anodes for internal reforming, lower temperature operation, and poison resistance, but there is a lack of study on the redox stability of the materials. In this work, the redox stability and electrochemcial performance of various oxides synthesized by solid-state and sol gel processes. The work focussed on mixed-conducting oxides with the perovskite and layered-perovskite crystal structures, but other similar structure families were also evaluated. The redox stability was measured using a controlled-atmosphere dilatometer. Two examples of compositions studied were doped-SrTiO3 and doped-Sr2B'B"O6-δ materials, which were subjected to >5 hours redox cycles in air and forming gas. Their linear expansion at isothermal conditions were compared to commonly used anode materials like Ni/YSZ and GDC. The change in microstructure of these samples after redox cycling were also studied. The electrical performance was also measured by four-point conductivity as a funciton of atmosphere changes, and this information was related to the defect and microstructure. Finally, the compostions showing the highest promise were tested in symmetrical cell and full fuel cell configurations to quantify their polarization resistance. Apart from the above-mentioned compositions, the redox and electrochemical performance of other non-traditional compositions with various doping strategy were also evaluated and will be discussed in this work.