Study of BaCe0.8Pr0.2O3-δ/BaCe0.4Zr0.4Y0.2O3-δ Bilayer Proton Conductor Electrolytes

BASBUS J.F.; WANG H; QING S; CANEIRO A.; TROIANI H.; MOGNI L.V

Congreso; 20th Topical Meeting of the International Society of Electrochemistry; 2017

Barium ceratesand zirconates are interesting materials due to their ability for transportingprotons through their crystal lattice. This feature and their stability at hightemperatures makes them potential candidates as hydrogen sensors, membranes forhydrogen purification and isotopic exchange (hydrogen, deuterium, tritium-H/D/T-) and as electrolytes for proton conductor solid oxide fuel andelectrolyzer cells (PC-SOFC). In previous works, we studied the BaCe0.8Pr0.2O3-δ(BCP) [1] and BaCe0.4Zr0.4Y0.2O3-δ  (BCZY) [2] oxides. We found that, whereas BCP electricalconductivity is dominated by a mixed (ionic and electronic) conductivity, especiallyunder O2-containing atmosphere, BCZY behaves as a pure protonconductor electrolyte. On the other hand, BCZY ionic bulk conductivity is oneor two order of magnitude higher than for BCP, however its grain boundaryconductivity is so low that compromises the use of this material as aproton-conductor membrane. Besides, CO2 tolerance is also animportant issue for these oxides. When they operate under low quality H2atmospheres, the same basicity that promotes H2O incorporation alsoinduces carbonate formation. In this sense, zirconates show much betterstability under CO2 containing atmospheres.Consideringthis, we propose a novel approximation: the use of a bilayer electrolyte withthe aim to combine the best properties of each material for its use as acomplex proton conductor membrane. Therefore, a thin layer (500 nm) of BCZY wasdeposited by Pulsed Laser Deposition (PLD) on a dense thick BCP electrolyte.The microstructure, composition and crystal structure of the thin layer and theBCP-BCZY interface was studied by grazing angle X-ray diffraction (GA-XRD), andelectron scanning (SEM) and transmission (TEM) microscopies. The transportproperties were studied by electrochemical impedance spectroscopy (EIS) as afunction of temperature (100 to 600 ºC) and atmosphere(H2-containing atmosphere and H2O or D2O wetair to analyze the isotopic effect). The EIS response of the bilayer electrolytewas analyzed by comparison with that of the BCP and BCZY single-layermembranes. The three systems (BCP, BCZY and BCP-BCZY) were evaluated in asingle chamber furnace by using Pt as current collector. The i-V curves of themembranes, working under atmospheric air and H2/Ar-mixture, werealso evaluated. The EIS responses were analyzed by using an electricalequivalent circuit, where it can be confirmed that the electronic conductivityof the BCP is blocked by the thin (and almost single crystal) BCZY layer. References[1] J. F.Basbus, M. D. Arce, F. Prado, L. Suescun, A. Caneiro, and L. V. Mogni. J.Electrochem. Soc., 163 (6), 2016, F516-F522.[2] J.F. Basbus,M.D. Arce, F.D. Prado, A. Caneiro, L.V. Mogni J. Power Sources 329 (2016) 262-267