Nanostructured Electrodes for Low Temperature Solid Oxide Fuel Cells

• Main Author: Benel, Cahit
• Format: Others
• Language: en
• Published: 2016
• Online Access: https://tuprints.ulb.tu-darmstadt.de/5846/1/thesis_benel.pdf; Benel, Cahit <http://tuprints.ulb.tu-darmstadt.de/view/person/Benel=3ACahit=3A=3A.html> (2016): Nanostructured Electrodes for Low Temperature Solid Oxide Fuel Cells.Darmstadt, Technische Universität, [Ph.D. Thesis]

The reduction of the operating temperatures of solid oxide fuel cells (SOFCs) below 600 °C is one of the primary objectives to make them cost competitive with existing energy conversion technologies. However, the low ionic conductivity of the electrolytes and the sluggish electrochemical reaction rates at the electrodes are the major issues, which limit the performance of SOFCs at reduced operating temperatures. While the effect of limited ionic conductivity of the electrolytes at lower operating temperatures has been compensated by decreasing the electrolyte thicknesses, the utilization of nanostructured electrodes with enhanced electrochemical activities has been one of the most common approaches to overcome the electrode limitations associated with the reduced operating temperatures. The aim of the thesis is to obtain high performance nanostructured electrodes for SOFCs in a cost-effective and easily scalable production method. The state-of-the-art electrode materials of La0.6Sr0.4CoO3-δ (LSC) and Ni-Ce0.8Gd0.2O2-δ (NiO-GDC20) with ultrafine microstructure and high phase purity are synthesized by salt-assisted spray pyrolysis method. Nanostructured electrode thin films fabricated by spin coating of the water-based dispersions of LSC and NiO-GDC20 nanoparticles exhibit a three-dimensional porous microstructure with a grain size of around 50 nm. The electrochemical performances of the resulting electrode layers with thicknesses below 1 µm are optimized in the symmetrical cell configuration for the purpose to integrate them into the micro-solid oxide fuel cell (micro-SOFC) devices, which typically employ costly physical vapor deposited Pt thin film electrodes. The proof of concept for the fabrication of porous micro-SOFC electrodes by spin coating of suspensions of electrode nanoparticles is reported for the first time, and the first set of electrochemical data (12 mW/cm2 at 500 °C) demonstrates the feasibility of the developed thin film electrode fabrication method. Furthermore, the synthesized electrode materials are examined in ceria-based anode supported SOFC design. The promising initial electrochemical results (318 mW/cm2 at 600 °C) set the ground for further optimization of the anode supported LSC|Ce0.9Gd0.1O2-δ (GDC10)|Ni-GDC20 cells.