The local structure of SOFC materials investigated by X-Ray absorption spectroscopy

Abstract

This chapter is devoted to the analysis of the local atomic structure of solid oxide fuel cell (SOFC) electrolyte and electrode materials. Among the experimental techniques able to provide information about the local structure of materials, the X-ray absorption spectroscopy has the peculiarity of element selectivity, allowing to investigate the chemical environment of specific atoms embedded in a matrix. Solid oxide electrolytes allow the conduction of ionic charge carriers between the electrodes of a SOFC device; the mechanism of ion conduction depends on the type of carrier, and it is finely tuned-or even only possible-if the solid matrix is suitably tailored by insertion of doping species that modify the local structure and the dynamics of the lattice. The oxygen reduction and fuel oxidation processes are catalyzed at the respective electrodes; moreover, the cathode and anode layers must: (1) allow an efficient exchange of reactants with the environment, (2) convey the ionic species to/from the electrolyte and (3) ensure the conduction of the electrons involved in the reduction and oxidation processes. The chemical and physical stability of the interface with the electrolyte layer is another essential issue of electrode materials. The chapter begins with a section describing the basic theory underlying the X-ray absorption spectroscopy and the experimental set-ups used in fuel cell applications. The second section reports on case studies and perspectives of future development of fuel cell materials under the keynote of local structure.