Neutron scattering for sustainable energy materials: investigations of proton dynamics in acceptor doped barium zirconates
Doktorsavhandling, 2018

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 BaZr0.9M0.1O2.95 with M=Y and Sc and BaZr1-xInxO3-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

neutron scattering

fuel cells

QENS

Proton conductors

perovskites

proton dynamics

energy materials

Lecture Hall KA, House Chemistry, Kemigården 4
Opponent: Roberto Senesi, Dipartimento di Fisica, Università degli Studi di Roma Tor Vergata, Italy

Författare

Daria Noferini

Chalmers, Fysik, Kondenserade materiens fysik

Institut Laue-Langevin

Proton Dynamics in Hydrated BaZr0.9M0.1O2.95 (M = Y and Sc) Investigated with Neutron Spin-Echo

Journal of Physical Chemistry C,; Vol. 120(2016)p. 13963-13969

Artikel i vetenskaplig tidskrift

Localized Proton Motions in Acceptor-Doped Barium Zirconates

Journal of Physical Chemistry C,; Vol. 121(2017)p. 7088-7093

Artikel i vetenskaplig tidskrift

D. Noferini, M. M. Koza, G. J. Nilsen, and M. Karlsson, Study of the Hydration Level in Proton Conducting Oxides Using Neutron Diffraction with Polarization Analysis.

Role of the doping level in localized proton motions in acceptor-doped barium zirconate proton conductors

Physical Chemistry Chemical Physics,; (2018)

Artikel i vetenskaplig tidskrift

The increasing world energy demand calls for sustainable technologies for energy conversion. Such technologies often depend on advanced materials with tailored characteristics. Research on materials science, pursuing the essential knowledge and know-how for their development, is thus at the service of society.

Hydrogen fuel cells are among the most important devices for energy conversion. However, to bring them into our everyday life, the challenge is to combine the advantages of a solid state conducting material with those of lowered operational temperatures (present ones are above 750 °C). A promising strategy to reach this goal is to use proton conducting oxides. Yet, a deep understanding of the proton conduction mechanism, that is how the protons move across the materials, is essential to design new conductors that meet the required properties for applications. To this aim, samples of barium zirconates, which are among the most promising proton conducting oxides, were experimentally characterized in this thesis using neutron scattering. With this technique it is possible to investigate both the structure (how the atoms are arranged) and dynamics (how the atoms move) of materials, by comparing the properties of a beam composed of neutrons before and after the collision with the sample. The obtained results provide important details to define a general mechanism of proton conduction and to understand how the fine tuning of the composition affects the performance of the proton conducting oxides. The new knowledge thus contribute to the further development of these materials and their applications.

Drivkrafter

Hållbar utveckling

Ämneskategorier

Keramteknik

Materialkemi

Annan materialteknik

Styrkeområden

Energi

Materialvetenskap

Fundament

Grundläggande vetenskaper

ISBN

978-91-7597-709-6

Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4390

Utgivare

Chalmers tekniska högskola

Lecture Hall KA, House Chemistry, Kemigården 4

Opponent: Roberto Senesi, Dipartimento di Fisica, Università degli Studi di Roma Tor Vergata, Italy