Study of Exsolved Nanocatalysts on Perovskite Oxide Supports for Solid Oxide Fuel Cells and Dry Reforming of Methane

Abstract

In the midst of a surge in future energy demand, heterogeneous catalysts play an essential role in building systems that effectively utilize available resources. When designing a catalyst, it is important to ensure stability and catalytic activity. Exsolution is an effective preparation tool, in this respect, because exsolution grows nanoparticles in-situ from the bulk lattice of support oxide under operating conditions. Accordingly, it gives "embedded" property and can prevent deactivation due to coarsening of catalyst through immobilization. Exsolution occurs with the formation of an oxygen vacancy in a reducing atmosphere. Therefore, methods such as temperature control, A-site non-stoichiometry, voltage biasing, lattice strain, and phase transition to make oxygen vacancy have been studied to control the degree of exsolution. In addition to these methods, we have been working on a unique method so-called topotactic exsolution. Topotactic exsolution further increases the number of active exsolved nanoparticles through the exchange with the internal target cation via the introduction of the external cation, contributing to the enhanced performance of the catalysts. That is, external cations fill the B-site vacancies within the perovskite, adding to the chemical stability of the structure of the catalyst while also ensuring catalytic activity. This simple yet original method is expected to lead to more research in the field of energy utilization as a way to maximize the advantages of exsolution, which can convert most of the potential cations to nanocatalysts. This dissertation focuses on the applications of an energy conversion device using topotactic exsolution, beginning with the basic and theoretical explanation of solid oxide fuel cell (SOFC) and dry reforming of methane (DRM). In chapter 2, a study on YBa0.5Sr0.5Co2-xFexO5+δ cathode to help overall understanding of SOFC, and in chapter 3, a study on the first topotactic exsolution, in chapter 4, extended study of topotactic exsolution using different cation, and in chapter 5, topotactic exsolution using atomic layer deposition (ALD) on simple perovskite support oxide are discussed.