ECI Digital Archives

Title

Defect chemistry of mixed conducting double Perovskites

Authors

Ragnar Strandbakke, University of Oslo, NorwayFollow
Tor S. Bjørheim, Dep. of Chemistry, University of Oslo, FERMiO, Gaustadalléen 21, Norway.
Magnus H Sørby, Inst. for Energy Technology, Department of Physics, Norway
Aleksandra Mielewczyk-Gryń, Faculty of Applied Physics and Mathematics, Solid State Physics Department, Gdańsk University of Technology, Poland
Sebastian Wachowski, Faculty of Applied Physics and Mathematics, Solid State Physics Department, Gdańsk University of Technology, Poland
Sebastian Wachowski, Faculty of Applied Physics and Mathematics, Solid State Physics Department, Gdańsk University of Technology, Poland
Truls . Norby, Dep of Chemistry, University of Oslo, FERMiO, Norway

Conference Dates

March 10-14, 2019

Abstract

Barium Gadolinium Lanthanum Cobaltites with the general formula Ba_1-xGd_0.8-yLa_0.2+x+yCo₂O_6-δ (BGLC) are reported as Mixed Proton and Electron Conducting materials (MPECs), and have been utilized as positrode (positive electrode) materials for Proton Ceramic Electrochemical Cells (PCECs) [1]. A defect chemical model, treating various charge carrying defects in BGLC was published in 2017 [2] and in this work we expand the model to also comprise formation of protons in BGLC. Protons can be incorporated by two different reactions, in a ratio depending on measurement conditions and the oxidation state of the material. Low temperatures and high pO₂ leaves BGLC oxidized, and with increasing electron hole concentration, the hydrogenation reaction is promoted with respect to hydration. Hydrogenation is confirmed by use of isothermal Dry-H₂O-D₂O switches in thermogravimetric measurements, revealing a larger concentration of protons than expected from hydration only (Figure 1, left). The reduction of BGLC by hydrogenation is slowly counteracted by oxygen uptake combined with an expected cation reordering, bringing the material back to its initial oxidation state after equilibration in wet conditions. By combining oxidation and hydration thermodynamics, hydrogenation entropy and enthalpy can be obtained, making it possible to model proton concentrations from hydration and hydrogenation separately by use of advanced defect chemistry (Figure 1, right). Hydration is proposed to be facilitated by a minor concentration of oxygen vacancies in the O-Co-O layers, where acidic vacancies may accommodate basic hydroxyl groups. These vacancies are neighboured by more basic oxide ions in the O-Ba-O and O-Ln-O layers which in turn may accommodate protons.

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Recommended Citation

Ragnar Strandbakke, Tor S. Bjørheim, Magnus H Sørby, Aleksandra Mielewczyk-Gryń, Sebastian Wachowski, Sebastian Wachowski, and Truls . Norby, "Defect chemistry of mixed conducting double Perovskites" in "Nonstoichiometric Compounds VII", ECI Symposium Series, (2019). https://dc.engconfintl.org/nonstoichiometric_vii/41