Structure and Thermal Behaviour of BSCF-SDC-Ag Composite Cathode for Solid Oxide Fuel Cell

Abstract

Solid oxide fuel cell (SOFC) component has always under development to enhance catalytic activity. Components such as anode, cathode and electrolyte must have better structure and behavior for good SOFC performance. Traditional Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) cathode in solid oxide fuel cell application has been deterred several inappropriate circumstances such as high thermal expansion coefficient (TEC) and chemical instability. Sm0.2Ce0.8O1.9 (SDC) electrolyte and Silver (Ag) are added into BSCF to overcome the problem and has better material characterization and thermal stability, The composite cathode powder BSCF-SDC was prepared by high speed ball milling technique with mixture of 50wt% BSCF and 50wt% SDC commercial powder. The powders were then dried and calcined at 950oC for 2 hour. Silver (Ag) with 1wt%, 3wt% and 5wt% were milled respectively with BSCF-SDC by low speed ball milling technique. The developed composite cathode was then examined by X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), dilatometer and Thermogravimetric Analysis (TGA). The vivid distinct phase of BSCF, SDC and Ag and absence of additional secondary phase was confirmed by XRD analysis indicating good phase structure compatibility. This also assured that less chemical reaction was happened during low speed milling process for BSCF-SDC-Ag as minor secondary phases are detected. However, milling process at high speed and high calcination temperature did destruct single phase of BSCF in BSCF-SDC composite cathode. However, Ag obtains its role to retain back the BSCF crystalline phase. The higher the percent of Ag added, the higher the BSCF peak retain. The absence of addition bonding in FTIR analysis demonstrating excellent structure compatibility of BSCF, SDC and Ag during milling process. There was no significant additional bonding appeared in BSCF-SDC-Ag after milling process. The thermal expansion coefficient (TEC) were determined using dilatometer, manifesting closer TEC mismatch between BSCF-SDC-Ag cathode composite and SDC electrolyte compared to BSCF-SDC. TEC is essential to be matched as it could prevent spallation during elevated operation temperature of SOFC. TGA analysis indicated cathode composite experiencing very less changes of weight when it was heated up 1000oC. BSCF is revealed of decomposition occurring after 800oC. Result revealed that Ag exhibited desirable thermal and structure compatibility with BSCF-SDC as promising SOFC cathode which beneficial from medium scale automobile to high scale power plant application.