Influence of the Ti Content on the Electrochemical Performance and Surface Properties of (La0.6Sr0.4)0.99Co1− xTixO3− δ Oxygen Electrode

Abstract

Mixed ionic and electronic conducting (MIEC) oxides are being used as solid oxide fuel cell (SOFC) electrode materials [1, 2]. La1− xSrxCoO3− δ (LSC) oxygen electrode has perovskite-type (ABO3) structure. The properties of these materials are determined by chemical composition, crystallographic structure and oxidation state of B-site elements. These electrode materials have good catalytic activity towards oxygen reduction reaction and oxide ion oxidation, but they have limited durability if carbon dioxide or humidity are presented in the electrode gas compartment. It is important to increase the long-term durability of these electrode materials at natural gas conditions, i.e. in gas from the external environment with micro-concentrations of impurities like water and carbon dioxide [3, 4, 5].The SOFC oxygen electrode powders with different stoichiometry ((La0.6Sr0.4)0.99Co1− xTixO3− δ , x = 0, 0.02, 0.04, 0.06, 0.08, 0.10) were prepared by using the thermal combustion method [6]. X-ray diffraction (XRD) analysis was used to characterize the crystallographic structure of the synthesized powders. Symmetrical cells for Electrochemical Impedance Spectroscopy (EIS), Focused Ion Beam Time of Flight Secondary Ions Mass Spectrometry (FIB-TOF-SIMS) and X-Ray Photoelectron Spectroscopy (XPS) were made using synthesized powders. Prepared symmetrical cells were characterized at different temperatures, potentials, gas compositions i.e. conditions.Systematic impedance analysis showed that materials with bigger cation (Ti4+), doped into the LSC B-site, increase the material long-term stability against impurities like carbon dioxide and water. As a result of the work, the optimal amount of dopant (Ti4+) was found, which increased the stability of the material in the environment with impurities.[1] C. Singhal, K. Kendall (Eds.), High-Temperature Solid Oxide Fuel Cells: Fundamentals, Design and Applications, Elsevier, Oxford, (2003).[2] Weber, E. Ivers-Tiffée, J. Power Sources 127, 273 (2004).[3] Kivi, J. Aruväli, K. Kiresimäe, A. Heinsaar, G. Nurk, E. Lust, J. Electrochemical Society, 160, F1022 (2013).[4] Kivi, J. Aruväli, K. Kirsimäe, P. Möller, A. Heinsaar, G. Nurk, E. Lust, J. Solid State Electrochem, 21, 361 (2017).[5] P. Jiang, Int J. Hydrogen Energy, 44, 7448 (2019).[6] P. Bansal, Z. Zhong, J. Power Sources, 158, 148 (2006).