Effect of Cation Ordering on the Performance and Chemical Stability of Layered Double Perovskite Cathodes

Carlos Bernuy-Lopez; Laura Rioja-Monllor; Takashi Nakamura; Sandrine Ricote; Ryan O'Hayre; Koji Amezawa; Mari-Ann Einarsrud; Tor Grande

doi:10.3390/ma11020196

Effect of Cation Ordering on the Performance and Chemical Stability of Layered Double Perovskite Cathodes

Materials (Basel). 2018 Jan 26;11(2):196. doi: 10.3390/ma11020196.

Authors

Carlos Bernuy-Lopez¹, Laura Rioja-Monllor², Takashi Nakamura³, Sandrine Ricote⁴, Ryan O'Hayre⁵, Koji Amezawa⁶, Mari-Ann Einarsrud⁷, Tor Grande⁸

Affiliations

¹ Department of Material Science and Engineering, NTNU Norwegian University of Science and Technology, NO-7491 Trondheim, Norway. carlos.bernuy-lopez@sandvik.com.
² Department of Material Science and Engineering, NTNU Norwegian University of Science and Technology, NO-7491 Trondheim, Norway. laura-rioja-monllor@ntnu.no.
³ Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1 Katahira Aoba-ku, Sendai 980-8577, Japan. t-naka@tagen.tohoku.ac.jp.
⁴ Department of Mechanical Engineering, Colorado School of Mines, Golden, CO 80401, USA. sricote@mines.edu.
⁵ Department of Metallurgical and Materials Engineering, Colorado School of Mines, 1500 Illinois St., Golden, CO 80401, USA. rohayre@mines.edu.
⁶ Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1 Katahira Aoba-ku, Sendai 980-8577, Japan. amezawa@tagen.tohoku.ac.jp.
⁷ Department of Material Science and Engineering, NTNU Norwegian University of Science and Technology, NO-7491 Trondheim, Norway. mari-ann.einarsrud@ntnu.no.
⁸ Department of Material Science and Engineering, NTNU Norwegian University of Science and Technology, NO-7491 Trondheim, Norway. tor.grande@ntnu.no.

Abstract

The effect of A-site cation ordering on the cathode performance and chemical stability of A-site cation ordered LaBaCo₂O_5+δ and disordered La_0.5Ba_0.5CoO_3-δ materials are reported. Symmetric half-cells with a proton-conducting BaZr_0.9Y_0.1O_3-δ electrolyte were prepared by ceramic processing, and good chemical compatibility of the materials was demonstrated. Both A-site ordered LaBaCo₂O_5+δ and A-site disordered La_0.5Ba_0.5CoO_3-δ yield excellent cathode performance with Area Specific Resistances as low as 7.4 and 11.5 Ω·cm² at 400 °C and 0.16 and 0.32 Ω·cm² at 600 °C in 3% humidified synthetic air respectively. The oxygen vacancy concentration, electrical conductivity, basicity of cations and crystal structure were evaluated to rationalize the electrochemical performance of the two materials. The combination of high-basicity elements and high electrical conductivity as well as sufficient oxygen vacancy concentration explains the excellent performance of both LaBaCo₂O_5+δ and La_0.5Ba_0.5CoO_3-δ materials at high temperatures. At lower temperatures, oxygen-deficiency in both materials is greatly reduced, leading to decreased performance despite the high basicity and electrical conductivity. A-site cation ordering leads to a higher oxygen vacancy concentration, which explains the better performance of LaBaCo₂O_5+δ. Finally, the more pronounced oxygen deficiency of the cation ordered polymorph and the lower chemical stability at reducing conditions were confirmed by coulometric titration.

Keywords: cathode; layered double perovskite; proton ceramic fuel cells (PCFC).