Tailoring the properties of a-site substituted Ba1-xGd0.8La0.2+xCo2O6-δ
September 4-8, 2016
The double perovskite BaGd0.8La0.2Co2O6-δ (BGLC) shows excellent performance as oxygen electrode for Proton Ceramic Fuel Cells (PCFCs) and electrolyzer cells (PCEC), with polarization resistances in wet oxygen of 0.04 and 10 Ωcm2 at 650 and 350 ⁰C, respectively . Compared with other reported PCFC cathodes , BGLC performs better both at high and low temperature. The excellent performance of BGLC in proton ceramic cells is rationalized by a suggested partial proton conductivity at intermediate temperatures, supported by significant hydration up to 400°C observed by thermogravimetric studies. However, the chemical stability of BGLC in high steam pressures under PCEC operation remains a concern due to its highly basic A-site. Thus, tailoring the A-site stoichiometry by partial substitution of Ba with La may be a viable route for further optimizing the balance between chemical stability and electrochemical performance.
In the literature we find numerous defect chemical models describing REBaCo2O5.5+δ-type double perovskites, but these are typically limited to describing the oxygen non-stoichiometry. Little can be found which relates defect chemistry to electrochemical performance, electrical conductivity or hydration behavior. Thus, this contribution aims to develop a global defect chemical model of the system Ba1‑xGd0.8La0.2+xCo2O6-δ (x = 0-0.5) by investigating its structural and functional properties as a function of Ba-site substitution. The complex structural behavior of Ba-site substituted BGLC is elucidated by combining synchrotron and neutron diffraction data with high temperature XRD to describe the local Co-O environment and the degree of cation and anion ordering as a function of temperature and pO2. The implications of A-site stoichiometry on proton incorporation are further investigated by thermogravimetric hydration studies supported by neutron powder diffraction of dry and deuterated samples. Finally, these properties are linked to oxygen non-stoichiometry, electrical conductivity and electrochemical performance to develop and validate our general defect chemical model for the system Ba1‑xGd0.8La0.2+xCo2O6-δ (x = 0-0.5).
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Einar Vøllestad, Ragnar Strandbakke, David Wragg, Sabrina Sartori, and Truls Norby, "Tailoring the properties of a-site substituted Ba1-xGd0.8La0.2+xCo2O6-δ" in "Nonstoichiometric Compounds VI", ECI Symposium Series, (2016). http://dc.engconfintl.org/nonstoichiometric_vi/22