Hydration and structural properties of mixed conductor Ba1‑xGd0. 8La0 Hydration and structural properties of mixed conductor Ba1‑xGd0.8La0.2+xCo2O6-δ (BGLC) Ragnar Strandbakke, Einar Vøllestad, Julien Lang, Matylda Natalia Guzik, Sabrina Sartori and Truls Norby

Double perovskites: Promising as PCFC / PCEC electrodes pH2O switches at 400 °C, total mass 2.5 g BaGd0.8La0.2Co2O6-δ (BGLC): Lowest reported ASR for PCECs 0.04 Ωcm2 at 700°C Proton incorporation suggested to facilitate fast electrode kinetics pH2O = 0.02 atm pH2O = 3 · 10−5 atm stability  structure  functional properties  defect chemistry Ba1‑xGd0.8La0.2+xCo2O6-δ (BGLC) R. Strandbakke et al, Solid State Ionics (2015)

Ba1‑xGd0.8La0.2+xCo2O6-δ (BGLC) Vøllestad et al., J. Mater. Chem. A, 2017, 5, 15743–15751

Hydration Isothermal switches from dry to wet (2% H2O) atmosphere in air

Hydration vs δ Isothermal switches from dry to wet (2% H2O) atmosphere in air

Hydration vs δ - Thermodynamics H (kJ mol-1) Kh vs δ High T 11 Low T -3

Oxygen vacancies on O2 and O3

GoPHy MiCO – Working hypothesis General double perovskite formula: AI1‑xAI*xAII1‑yAII*yB2‑zB*zO6‑δ Can we – by substitutions on A1, A2 or B sites – induce oxygen vacancies with acidic character in the O-Co-O layer? If so – will these vacancies be prone to hydration?

Hydration of vO(2) Vøllestad et al., J. Mater. Chem. A, 2017, 5, 15743–15751

Hydration of vO(2) - Thermodynamics Kh vs δ High T 11 Low T -3 Kh vs -28 -46 H(kJ mol-1) Kh vs δ High T 11 Low T -3 Van’t Hoff plots of hydration K’s vs δ and

Hydration – Modelling of [OH] vs vO(2)

Hydration – Modelling of [OH] vs vO(2) H(kJ mol-1) Kh vs δ High T 11 Low T -3 Kh vs vO2 -28 -46 Kh acid / base -36

Hydration and hydrogenation Dependent on T and pO2 High pO2 Low pO2 Dry Wet Dry Dry Wet Dry High pO2 / low T Low pO2 / high T

Hydrogenation – reduction of Co by oxidation of steam to O2 Co (4+) to Co (3+) How to define electronic defects?

Available O sites: 6 (1+4+1) Defects A1 A2 O1 O2 O3 Reference states Oxidation state: Co3.5+ Available O sites: 6 (1+4+1) Electrons / electron holes Ionic defects Co4+: Co3+: Co2+: Vøllestad et al., J. Mater. Chem. A, 2017, 5, 15743–15751

Hydrogenation – reduction of Co by oxidation of steam to O2 Co (4+) to Co (3+) δ Vøllestad et al., J. Mater. Chem. A, 2017, 5, 15743–15751

Hydration and Hydrogenation Red-ox Acid / base S(J mol-1 K-1) H(kJ mol-1) Kh vs d High T -50 11 Low T -70 -3 Kh vs vO2 -79 -28 -106 -46 Kh acid / base -88 -47 Khy red-ox -152 -31

Stability in low steam pressures Powders kept in 2.7% H2O at 300°C for 20 hrs. --- BGLC (X = 0), wet --- BGLC (X = 0), dry

Stability in high steam pressures Powders kept in 1.5 bars of steam at 600°C for 72 hrs. Reaction assumed to be completed --- BGLC (X = 0), wet --- BGLC (X = 0), dry Hexagonal BaCoO3

Stability in high steam pressures Powders kept in 1.5 bars of steam at 600°C for 72 hrs. --- X = 0.5, wet --- X = 0.4, wet --- X = 0.2, wet --- X = 0, wet Hexagonal BaCoO3

Two crystalline phases (P4/mmm): High Resolution Synchrotron Powder X-Ray Diffraction (HR SR-PXD) X = 0 Two crystalline phases (P4/mmm): Double perovskite (1x1x2) Superstructure (3x3x2) So, based on this assumption, the data were refined against four models that consisted of two phases. Model 1: (1) double perovskite unit cell of BaGd1-xLaxCo2O6-d (P4/mmm, 1x1x2) + (2) superstructure cell of BaGdCo2O6-d (P4/mmm, 3x3x1) Tetr refined values of lattice constants: a1 = 3.8886(1) , c1 = 7.5830(3) Å; a2 = 10. 9462(7) , c2 = 3.7236(6) Å Model 2: double perovskite unit cell of BaGd1-xLaxCo2O6-d (P4/mmm, 1x1x2) + superstructure cell of BaGdCo2O6-d (Pmmm, 3x3x1) Orth refined values of lattice constants: a1 = 3.8886(1) , c1 = 7.5830(3) Å; a2 = 10. 9079(7) , b2 = 11.0064(7), c2 = 3.7236(6) Å Model 3: double perovskite unit cell of BaGd1-xLaxCo2O6-d (P4/mmm, 1x1x2) + superstructure unit cell of BaGdCo2O6-d (P4/mmm, 3x3x2) refined values of lattice constants: a1 = 3.8886(1) , c1 = 7.5830(3) Å; a2 = 10. 9856(5) , c2 = 7.4529(5) Å Model 4: double perovskite unit cell of BaGd1-xLaxCo2O6-d (P4/mmm, 1x1x2) + superstructure unit cell of BaGdCo2O6-d (Pmmm, 3x3x2) Orth refined values of lattice constants: a1 = 3.8886(1) , c1 = 7.5830(3) Å; a2 = 10. 9286(5), b2 = 11.0113(6) c2 = 7.4552(4) Å Only very subtle changes among all models were obesrved but the best agreement has been obtained for Model 3 and this one will be used for further refinements against neutron data.

Two crystalline phases (P4/mmm): High Resolution Synchrotron Powder X-Ray Diffraction (HR SR-PXD) X = 0 Two crystalline phases (P4/mmm): Double perovskite (1x1x2) Superstructure (3x3x2) Ba Ln Co O So, based on this assumption, the data were refined against four models that consisted of two phases. Model 1: (1) double perovskite unit cell of BaGd1-xLaxCo2O6-d (P4/mmm, 1x1x2) + (2) superstructure cell of BaGdCo2O6-d (P4/mmm, 3x3x1) Tetr refined values of lattice constants: a1 = 3.8886(1) , c1 = 7.5830(3) Å; a2 = 10. 9462(7) , c2 = 3.7236(6) Å Model 2: double perovskite unit cell of BaGd1-xLaxCo2O6-d (P4/mmm, 1x1x2) + superstructure cell of BaGdCo2O6-d (Pmmm, 3x3x1) Orth refined values of lattice constants: a1 = 3.8886(1) , c1 = 7.5830(3) Å; a2 = 10. 9079(7) , b2 = 11.0064(7), c2 = 3.7236(6) Å Model 3: double perovskite unit cell of BaGd1-xLaxCo2O6-d (P4/mmm, 1x1x2) + superstructure unit cell of BaGdCo2O6-d (P4/mmm, 3x3x2) refined values of lattice constants: a1 = 3.8886(1) , c1 = 7.5830(3) Å; a2 = 10. 9856(5) , c2 = 7.4529(5) Å Model 4: double perovskite unit cell of BaGd1-xLaxCo2O6-d (P4/mmm, 1x1x2) + superstructure unit cell of BaGdCo2O6-d (Pmmm, 3x3x2) Orth refined values of lattice constants: a1 = 3.8886(1) , c1 = 7.5830(3) Å; a2 = 10. 9286(5), b2 = 11.0113(6) c2 = 7.4552(4) Å Only very subtle changes among all models were obesrved but the best agreement has been obtained for Model 3 and this one will be used for further refinements against neutron data.

? High Resolution Synchrotron Powder X-Ray Diffraction (HR SR-PXD) La Ba1-xGd0.8La0.2+xCo2O6-δ X = 0-0.5 La Simple cubic emerging: LaCoO3 coexisting with double perovskite phase HR SR-PXD data were collected at BM31 of Swiss-Norwegian Beamlines, at ESRF in Grenoble (France). Powders were sealed in a boronglass capillary with an internal diameter d = 3 mm and measured over an angular range of 1-35 ° 2θ with a step size of 0.006 ° 2θ. The wavelength (λ = 0.50506 Å) was calibrated using Si as a standard material. (BTW, this is not spectra since the measured intenity does not depend on energy or any parameter directly related with energy. Here, the intenisity depends only on diffraction angles (2-theta)). Powder diffraction data sets colleted for series of dry samples is presented in the slide (left), zoom of the angular range 6-20 ° 2θ (right). Though the main peaks are obesrved in all presented patterns there are other reflections, which change with increasing concentration of La (see arrows) Double perovskite LaCoO3 La BaCoO3 Super structure ? Ba

Hydration – SR-PXRD and NPD HR SR-PXD and Powder Neutron Diffraction (PND) for BGLC: Dried and deuterated samples --- BGLC wet --- BGLC dry PND We started with analysis of 1082 sample, for which also neton powder diffraction (PND) experiments were carried out (samples sealed in a vanadium container, λ = 1.3280 Å). Both Dry and Wet powders were measured and data were compared. No diffrence was observed between SR-PXD data for Dry and Wet powders but there were changes in intenisties of PND data (arrows). In order to explain observed modifications, the strutural analysis (Rietveld refinement) of the data has been perormed. Extra Bragg peaks of deutereated sample: Secondary phase No indication in SR-XRD Oxygen peak Also related to hydration Deuterium in the structure