Beyond the 3rd Generation of Planar SOFC: Development of Metal Foam Supported Cells with Thin Film Electrolyte

Manufacturing of thin and gas tight electrolyte is still a challenging issue for metal supported solid oxide fuel cells (SOFCs). In this work, we present a porosity graded multi-layer structure supporting thin film electrolyte. The substrate is made of NiCrAl metal foam impregnated with La-substituted SrTiO₃ (LST) ceramic. Furthermore, a 20 µm thick composite anode functional layer with LST and gadolinium doped ceria (GDC) was deposited onto the substrate. The surface of the anode functional layer is later engineered with a suspension of nano-particles with 40 nm average particle size of yttria-stabilized zirconia (YSZ). This results in a mesoporous layer with smooth surface able to support a thin film GDC layers. Finally, a gas-tight GDC electrolyte was deposited by EB-PVD method. The thickness of the thin-film YSZ layer and the gas-tight GDC layer was approximately 1 µm and 2 µm, respectively. Button half cells with size up to 25cm² were successfully produced showing an air leakage rate down to 7.0*10^-4 (hPa*dm³)/(s*cm²), satisfying the gas-tightness quality control threshold of the state of the art metal supported SOFCs at DLR. Full cells with LSCF cathodes were then produced and electrochemically tested presenting stable Open Circuit Voltage near to 1V. Results will be presented and discussed in this paper by confronting the performance with the cell microstructure.

Key Words: metal foam, thin-film, electrolyte

The research leading to these results has received funding from the European Union‘s Seventh Framework Programme (FP7/2007-2013) for the Fuel Cells and Hydrogen Joint Technology Initiative under grant agreement n° 303429