In situ neutron scattering studies of energy materials

Abstract

Climate change presents a significant challenge to humanity. In order to slow the impact of climate change, energy conversion technologies have to increase the efficiencies of energy conversion processes. Advances such as solid oxide fuel cells (SOFC) and viable hydrogen storage materials will make a sizeable contribution to the drive for greater energy efficiency.

The research presented here focuses on in situ neutron scattering studies of energy materials. Multiple different neutron diffraction and spectroscopic techniques were employed to probe the structure and properties of potential SOFC anode materials, and alkaline earth hydrides (potential hydrogen storage materials).

In situ neutron diffraction was utilised to observe the evolution of exsolving nanoparticles in a nickel-doped lanthanum cerium titanate perovskite, which is analogous to potential SOFC materials. Structural changes in the perovskite parent material and the size evolution of the nanoparticles were observed, and the level of strain in the particles determined. Complementary electron microscopy and thermogravimetric data combined to develop a complete picture of nanoparticle exsolution.

The pinnacle of the research was the development and use of a sample environment for in situ combined neutron diffraction and impedance analysis at elevated temperatures and under multiple gas atmospheres. The capability of the sample environment was demonstrated through an isotope effect experiment where deuterium in alkaline earth hydride samples was exchanged for hydrogen in situ while measuring impedance. Very clear correlation between changing sample resistance and the atomic occupancy ratios of hydrogen to deuterium in the crystal structures was shown, and the isotope effect was a strong piece of evidence for pure hydride ion conduction in these materials.

Hydride ion diffusion was then further investigated in barium hydride through quasi elastic neutron scattering. The data showed clear evidence for the bulk diffusion of hydrogen nuclei in the material, with jump lengths, residence times and diffusion coefficients determined through fitting of a jump-diffusion Chudley Elliot model to the data.

Date of Award	22 Jun 2016
Original language	English
Awarding Institution	University of St Andrews
Supervisor	John Thomas Sirr Irvine (Supervisor) & Cristian Daniel Savaniu (Supervisor)