International Journal of Hydrogen Energy, Volume 39, Issue 24, 2014, Pages 12804–12811.
Abul K. Azad1,2, Angela Kruth3, John T.S. Irvine1.
1 School of Chemistry, University of St Andrews, Fife KY16 9ST, UK.
2 Faculty of Integrated Technologies, University Brunei Darussalam, Gadong BE 1410, Brunei Darussalam.
3 Leibniz Institute for Plasma Science and Technology, INP, Felix-Hausdorff-Str. 2a, 17489 Greifswald, Germany.
High-resolution neutron powder diffraction data were collected at different temperatures and pressure under hydrogen or oxygen under high and low humidities. The samples were loaded in sealed quartz tubes in dry or wet conditions at 0.33 atm pressure and 295 K temperature, and heated up to 973 K during measurements. Rietveld refinement of neutron diffraction data showed that the structure changed from primitive orthorhombic (space group Pbnm) to body centred orthorhombic (Imma) to rhombohedral (R-3c) on heating from room temperature to 973 K. At 623 K temperature and 0.71 atm pressure, the unit-cell volume is higher in wet hydrogen and oxygen atmosphere than dry atmosphere due to proton uptake. Oxygen site occupancies were directly determined as functions of temperature for dry and wet conditions in both oxidising and reducing conditions in order to probe actual oxygen/hydroxyl contents under the conditions relevant to most fuel cell or transport studies.
Fuel cells are promising technology to generate electricity and heat from hydrogen and oxygen. Renewable sources, like sun and wind, can produce electricity only depending on the availability of the resources. But they can, for example, produce electricity and hydrogen, which can be stored until it’s needed. Hydrogen can be used in fuel cells to produce energy. Intermediate temperature solid oxide fuel cells produce electricity at about 600 oC mainly using solid proton conducting electrolytes. BaCe0.9Y0.1O3-d, a proton conducting electrolyte, is very promising for its high proton conductivity. Proton conductivity maximizes in humid and hydrogen/oxygen condition. Looking into the mechanism of proton conductivity by neutron diffraction is important and interesting because of neutrons ability to interact with the nucleus to get internal information. Neutron diffraction is also the most direct method to locate light atoms like hydrogen and oxygen in a crystal structure. Samples were loaded in quartz tubes in dry or wet hydrogen and oxygen at ambient temperature and 0.33 atm pressure. In-situ measurements were carried out by increasing the temperature and pressure. Neutron powder diffraction measurements were carried out at different temperature and pressure in order to investigate the structural phase changes in oxygen and hydrogen rich atmospheres. BaCe0.9Y0.1O3-d contains a number of oxygen vacancies allowing for increased number of oxygen/proton incorporation at high temperatures, thereby potentially allowing for the reliable identification of the proton sites. Combined approach of Rietveld refinement and Fourier nuclear density map to find the way of proton transport.