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- Noferini, Daria, 1983
(författare)
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Neutron scattering for sustainable energy materials: investigations of proton dynamics in acceptor doped barium zirconates
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Proton conducting oxides are currently receiving considerable attention for their present or potential use as electrolytes in technological devices such as sensors and electrolysers and, in particular, solid oxide fuel cells, which are among the most promising apparatuses for energy conversion. One of the main challenges for these latter devices is to combine the advantages of a solid electrolyte with those of operational temperatures below 750 °C, which is currently hampered by insufficient conductivities in the targeted temperature range. The development of new electrolytes meeting the requirements for applications depends on a better understanding of the physico-chemical processes underlying ionic conductivity in these materials. Towards this aim, this thesis reports on investigations of key properties in hydrated samples of the perovskites BaZr0.9 M 0.1O2.95 with M =Y and Sc and BaZr1- x In x O3- x /2 with x =0.1—0.275, well-known and promising proton conducting oxides. Of specific concern in this thesis is the study of the effect of the type ( M ) and concentration ( x ) of dopant atoms on the atomic-scale proton dynamics over a wide time-range, from picoseconds to nanoseconds, using different state-of-the-art neutron scattering techniques at the neutron scattering facilities Institut Laue-Langevin in Grenoble, France, and Forschungs-Neutronenquelle Heinz Maier-Leibnitz in Garching, Germany. The results show a complex dynamics, arising from a distribution of different proton sites, a consequence of a disordered structure of the materials. Analysis of the short time scale dynamics discloses localized dynamics interpretable as proton jumps and reorientations of the hydroxyl groups. Faster local motions are observed in more distorted structures associated with higher doping levels, whereas no substantial differences are observed for different dopant ions. Analysis of the long time scale dynamics reveals long-range diffusion of protons, which can be described as a jump-diffusion process. Higher dopant concentrations lead to higher activation energies, still well below those for macroscopic proton conductivities, but larger fractions of mobile protons. This new insight adds to the previous knowledge of proton dynamics in perovskite materials and can be useful to develop strategies for the design of improved proton conductors for technological applications
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| 2. |
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| 3. |
- Noferini, Daria, 1983, et al.
(författare)
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Role of the doping level in localized proton motions in acceptor-doped barium zirconate proton conductors
- 2018
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 20:20, s. 13697-13704
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Tidskriftsartikel (refereegranskat)abstract
- Acceptor-doped barium zirconates are currently receiving considerable interest because of their high proton conductivity at intermediate temperatures, making them applicable as electrolytes in various electrochemical devices, but the mechanism of proton conduction is unclear. Here, we investigate the role of the acceptor-dopant level in the localized proton motions, i.e. proton transfers between oxygens and O-H reorientations, in hydrated samples of the proton conducting, acceptor-doped, perovskites BaZr1-xInxO3-x/2 with x = 0.10 and 0.20, using quasielastic neutron scattering (QENS). Analysis of the QENS spectra reveals that several proton transfer and O-H reorientational motions contribute to the QENS signal, as a consequence of the locally disordered nature of the structure due to the In doping of these materials, and establishes a generic and complex picture of localized proton dynamics in acceptor-doped barium zirconate based proton conductors. A comparison of the QENS results with vibrational spectroscopy data of the same materials, as reported in the literature, suggests a predominance of O-H reorientational motions in the observed dynamics. The highest doping level corresponds to a more distorted structure and faster dynamics, which thus indicates that some degree of structural disorder is favourable for high local proton mobility.
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| 4. |
- Noferini, Daria, 1983, et al.
(författare)
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Study of the hydration level in proton conducting oxides using neutron diffraction with polarization analysis
- 2018
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Ingår i: Solid State Ionics. - : Elsevier BV. - 0167-2738. ; 324, s. 163-167
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Tidskriftsartikel (refereegranskat)abstract
- We report results from neutron diffraction with polarization analysis of the effect of In dopant level on the hydrogen concentration in hydrated samples of the proton conducting perovskite type oxide BaZr1−xInxO3−x/2with x = 0, 0.175, 0.20, 0.225, 0.25, and 0.275. Analysis of the neutron data establishes a trend of increasing hydrogen concentration, which is comparable to that obtained from thermogravimetric measurements on the same samples, as well as an increased unit-cell size and local structural disorder as a function of increasing In dopant level. These results encourage further use of neutron diffraction with polarization analysis as a non-destructive technique for the determination of the total hydrogen concentration, and structural properties, of proton conducting oxides as well as other hydrogen-containing materials.
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