Combinatorial Search for new mixed electronic ionic materials for SOFC Cathode Applications
Creators: name: Rossiny, Jeremy Claude Henri
Publisher: name: Imperial College London
Year: 2011

description: In order to lower SOFC operating temperature between the range of 500 and 800°C, research has been focussed on finding alternative cathode materials, as it is where the highest area specific resistivity in the ceramic cell is exhibited. There is a constant requirement for novel high performance mixed conducting oxides for a variety of applications including cathodes for solid oxide fuel cells and as oxygen separation membranes. The conventional method of approaching this problem is by synthesising oxide compositions obtained from consideration of crystal structure and chemistry. One consequence of this is that synthesis is limited to a few chosen compositions because of the time consuming nature of the synthesis process. A way round this is the use of combinatorial methods to explore much wider ranges of compositions based upon rational choices of starting compositions. An interdisciplinary project was launched to use an ink jet based robot system, LUSI (London University Search Instrument), in order to synthesise combinatorial arrays of ceramic dot samples (2mm dia 500μm high) suitable for measurement of oxygen transport. More information on the robot and the project can be found on the related project web page www.foxd.org. The aim is to use oxygen 18 isotopic exchange with an array together with high resolution SIMS to identify materials with a high degree of exchange with oxygen gas at a given temperature. The first part of this programme was aimed at producing arrays of materials for which the transport properties are well known and to this end we have started with the perovskite materials with the general formula La1-xSrxCo1-yMnyO3, for which we have enough previous information to verify that the experimental protocols are correct. This study was followed by the study of a less known composition space with the general formula La1-xSrxCo1-y-zMnyFezO3. Quality synthesis of automated ink-jet printed samples has been carried out and composition (Induced Couple Plasma Mass Spectrometry), structure determination (X-ray diffraction and Raman Spectrometry) and oxygen content (Thermogravimetric and Catalysis Temperature-programmed Desorption) have been characterised systematically over the full range of compositions prior to performing the isotopic exchange procedure. Isotopic exchange procedures have been written, and tested on one composition. A new diffusion algorithm has been coded to take into account the shape of the combinatorial samples. Design of a new high-throughput technique has been created and this technique has been tested to identify new SOFC cathode materials. A first systematic study has been carried out over the full range of composition of general formula La1-xSrxCo1-y-zMnyFezO3. An automated production of thick-film perovskites has been achieved to a certain extent: composition, phase and oxygen non stoichiometry have been characterised over the full composition of the La0.8Sr0.2Co1-y-zMnyFezO3 pseudo-ternary solid solution. The isotopic exchange technique has been carried out on the La0.8Sr0.2MnO3 and La0.8Sr0.2CoO3 samples.