Interaction of H2O, O2 and H2 with Proton Conducting Oxides Based on Lanthanum Scandates

The research uses the method of high-temperature thermogravimetric analysis to study the processes of interaction of the gas phase in the temperature range 300–950 °C in the partial pressure ranges of oxygen 8.1–50.7 kPa, water 6.1–24.3 kPa and hydrogen 4.1 kPa with La1–xSrxScO3–α oxides (x = 0; 0.04; 0.09). In the case of an increase in the partial pressure of water vapor at a constant partial pressure of oxygen (or hydrogen) in the gas phase, the apparent level of saturation of protons is shown to increase. An increase in the apparent level of saturation of protons of the sample also occurs with an increase in the partial pressure of oxygen at a constant partial pressure of water vapor in the gas phase. The paper discusses the causes of the observed processes. The research uses the hydrogen isotope exchange method with the equilibration of the isotope composition of the gas phase to study the incorporation of hydrogen into the structure of proton-conducting oxides based on strontium-doped lanthanum scandates. The concentrations of protons and deuterons were determined in the temperature range of 300–800 °C and a hydrogen pressure of 0.2 kPa for La0.91Sr0.09ScO3–α oxide. The paper discusses the role of oxygen vacancies in the process of incorporation of protons and deuterons from the atmosphere of molecular hydrogen into the structure of the proton conducting oxides La1–xSrxScO3–α (x = 0; 0.04; 0.09). The proton magnetic resonance method was used to study the local structure in the temperature range 23–110 °C at a rotation speed of 10 kHz (MAS) for La0.96Sr0.04ScO3–α oxide after thermogravimetric measurements in an atmosphere containing water vapor, and after exposures in molecular hydrogen atmosphere. The existence of proton defects incorporated into the volume of the investigated proton oxide from both the atmosphere containing water and the atmosphere containing molecular hydrogen is unambiguously shown. The paper considers the effect of the contributions of the volume and surface of La0.96Sr0.04ScO3–α oxide on the shape of the proton magnetic resonance spectra.

1. Bi, L. Steam electrolysis by solid oxide electrolysis cells (SOECs) with proton-conducting oxides / L. Bi, S. Boulfrad, E. Traversa // Chemical Society Reviews. – 2014. – Vol. 43(24). – P. 8255–8270.

2. Hübert, T. Hydrogen sensors – A review / T. Hübert [et al.] // Sensors and Actuators B. – 2011. – Vol. 157. – 329–352.

3. Malerød-Fjeld, H. Thermo-electrochemical production of compressed hydrogen from methane with near-zero energy loss / H. Malerød-Fjeld [et al.] // Nature Energy. – 2017. – Vol. 2. – P. 923–931.

4. Fabbri, E. Towards the next generation of Solid Oxide Fuel Cells operating below 600°C with chemically stable proton‐conducting electrolytes / E. Fabbri [et al.] // Advanced Materials. − 2012. – Vol. 24(2). − P. 195−208.

5. Norby, T. Solid-state protonic conductors: principles, properties, progress and prospects / T. Norby // Solid State Ionics. – 1999. – Vol. 12. – P. 51–11.

6. Kreuer, K.D. Proton-conducting oxides. / K.D. Kreuer // Annual Review of Materials Research. – 2003. – Vol. 33. – P. 333–359.

7. Gorelov, V.P. Solid proton conducting electrolytes based on LaScO3 / V. P. Gorelov, A.Yu. Stroeva // Russian Journal of Electrochemistry. – 2012. – Vol. 48. – P. 949–960.

8. Stroeva, A.Yu. Phase composition and conductivity of La1−xSrxScO3−α (x = 0.01−0.20) under oxidative conditions / A.Yu. Stroeva [et al.] // Russian Journal of Electrochemistry. – 2012. – Vol. 48. – P. 509–517.

9. Stroeva, A.Yu. Nature of conductivity of perovskites La1−xSrxScO3−α (x = 0.01−0.15) under oxidative and reducing conditions / A.Yu. Stroeva, V.P. Gorelov // Russian Journal of Electrochemistry. – 2012. − Vol. 48. – P. 1079–1085.

10. Farlenkov, A.S. Water Uptake, Ionic and Hole Transport in La0.9Sr0.1ScO3–δ / A.S. Farlenkov [et al.] // Solid State Ionics. – 2017. – Vol. 306. − P. 126−136.

11. Okuyama, Y. Incorporation and conduction of proton in Sr-doped LaMO3 (M = Al, Sc, In, Yb, Y) / Y. Okuyama [et al.] // Electrochimica Acta. – 2014. – Vol. 125. – P. 443–449.

12. Farlenkov, A.S. Local disorder and water uptake in La1–xSrxScO3–δ / A.S. Farlenkov [et al.] // Solid State Ionics. – 2017. − Vol. 306. − P. 82−88.

13. Ananyev, M.V. Isotopic exchange between hydrogen from the gas phase and proton-conducting oxides: Theory and experiment / M.V. Ananyev, A.S. Farlenkov, E.Kh. Kurumchin // International Journal of Hydrogen Energy. – 2018. – Vol. 43. – P. 13373−13382.

14. Vlasov, M.I. Local levels in La1−xSrxScO3−x/2 band-gap under interaction with components of O2, H2, H2O atmospheres / M.I. Vlasov [et al.] // International Journal of Hydrogen Energy. − 2018. − Vol. 43. − P. 17364−17372.

15. Vlasov, M.I. Effect of Proton Uptake on the Structure of Energy Levels in the Band-Gap of Sr-doped LaScO3: Diffuse Reflectance Spectroscopy and Coherent Potential Approximation Calculations / M.I. Vlasov [et al.] // Physical Chemistry Chemical Physics.− 2019. − Vol. 21– P. 7989−7995.

16. Pinaeva, L.G. 1H- and V-51 high-resolution solid-state nuclear-magnetic-resonance studies of supported V2O5/TiO2 catalysts / L.G. Pinaeva [et al.] // Journal of Molecular Catalysis. − 1994. − Vol. 88. − P. 311−323.

17. Nosaka, A.Y. Characteristics of water adsorbed on TiO2 photocatalytic surfaces as studied by 1H NMR spectroscopy / A.Y. Nosaka, Y. Nosaka // Bulletin of Chemical Society of Japan. – 2005. – Vol. 78. – P. 1595–1607.