Microscopic characterisation of metal nanoparticle exsolution in Ni-doped A-site deficient perovskite titanate

Hydrogen technology has been of interest to meet the high demands for the clean, renewable and sustainable energy sources. Solid oxide fuel cells (SOC) have caught the attention because it many advantages including high efficiency and reversibility which enables both production and re-electrification of the hydrogen. Current state of the art SOCs electrodes are based on Ni-YSZ materials but recently research conducting the application of perovskite-based electrode with exsolution have been gaining interest because it can provide improve cell performance and resistance against coking and impurity poisoning as opposed to Ni-YSZ. Perovskite is known for its unique ability to produce metal nanoparticles on its surface when exposed to high temperatures under a reducing atmosphere which is known as exsolution. The exsolution of perovskite has been suggested as an alternative approach to producing active and durable supported nanoparticle system as it can provide highly active and durable nanoparticles through a simple, single step synthesis procedure that has been limitations of the conventional approaches such as depositions. This made the exsolved perovskite material applicable in a wide range of electrochemical systems includes but not limited to SOC. Understanding the mechanism of exsolution and defect chemistry of perovskite will enable optimisation of the formation of nanoparticles to the need. This thesis explores characterisation of Ni nanoparticle exsolution in A-site deficient perovskite titanates (Aₒ.₈BO3, A = La³⁺, Sr²⁺, Ca²⁺ and Nd³⁺). First, a series of perovskites with different degree of oxygen vacancies is investigated. Secondly, the influence of Sr²⁺/Ca³⁺ cations on the perovskite exsolution is explored. Lastly, an investigation of the role of rare earth element, Nd³⁺ on the exsolution process is performed. The morphology of the exsolution in each perovskite is compared and analysed with respect to surface orientation. This thesis also demonstrates a quantitative characterisation method through combining EBSD, SEM, FIB and TEM techniques of electron microscopy.