Electrical Performance of Ag-Based Ceramic Composite Electrodes and Their Application in Solid Oxide Fuel Cells

Silver-based ceramic composite electrodes are expected to be widely applied in medium- or low temperature solid oxide fuel cells (SOFCs), SOFCs operated on carbon-containing fuels, and solid oxide electrolysis cells (SOECs). To optimize the composition of a silver-based ceramic composite electrode, the performances of Ag-YSZ (yttrium-stabilized zirconia) and Ag-GDC (gadolinium doped ceria) are investigated. First, they are used as electrode materials to make symmetric electrodes on a YSZ electrolyte, to which impedance spectra are measured in an ambient atmosphere to evaluate their feasibility as cathode materials. It was found that that Ag-YSZ reaches the lowest polarization resistance when the content of Ag is 65% (w, mass fraction), while for Ag-GDC, the value is 70% (w). The Ag-YSZ and Ag-GDC with the lowest polarization resistance are used as electrode materials to make SOFC single cells whose electrochemical performances are tested. The polarization resistance of an anode of the SOFCs can be obtained by subtracting the cathode polarization resistance from the overall SOFC polarization resistance. Both the polarization resistance result and the output performance show that the performance of Ag-GDC is superior to Ag-YSZ as an anode. In the present work, Ag-YSZ is more suitable as the cathode and the Ag-GDC as the anode. The present work provides not only useful data for Ag-based composite electrodes but also a method for measuring the polarization resistance of SOFC anodes.