Microstructural and electrochemical characterization of thin La_(0.6)Sr_(0.4)CoO_(3-δ) cathodes deposited by spray pyrolysis

摘要

Mixed ionic-electronic conducting La_(0.6)Sr_(0.4)CoO_(3-δ) (LSC) has recently drawn much attention as one of the most active materials for intermediate temperature SOFC cathodes. The electrochemical kinetics is believed to be limited by oxygen incorporation at the perovskite/air interface. Hence improvement of the cathode performance can be achieved by increasing the number of sites for oxygen exchange. This is realized either by making the electrode thicker and/or by producing nanosized LSC grains. Spray pyrolysis (SP) constitutes a cost-effective alternative technique to vacuum-based deposition techniques, such as pulsed laser deposition (PLD) and sputtering, to produce such nanocrystalline components for thin films SOFC and micro-SOFC. Its versatility in terms of processing parameters (e.g. deposition temperature, precursor concentration, flow rate …) enables to fabricate a large variety of electrodes with various microstructures, grain sizes and pore sizes. In this work, nanoporous La_(0.6)Sr_(0.4)CoO_(3-δ) cathodes are sprayed on yttria-stabilized zirconia (YSZ) and gadolinium-doped ceria (GDC) electrolyte substrates. As-deposited layers are amorphous. The desired perovskite phase, electrical conductivity and porosity develop upon annealing at ca. 500-600°C. Grain and pore size from 10 to 50 nm can be obtained by adjusting the heat-treatment of the as-deposited layers. Power density data of anode- supported SOFC shows that SP-LSC and PLD-LSC cathodes yield similar electrochemical performance in the 450-650 °C range. This contribution will also present quantitative microstructure analyses of annealed electrodes (such as specific surface area, constrictivity and tortuosity, using continuous phase size distribution), area-specific resistance values of LSC/GDC (or YSZ)/ LSC symmetrical cells as well as results on the SP-LSC/YSZ chemical compatibility and the need of a GDC interlayer.