(535i) Low-Temperature Fabrication of Dense Ba(Zr,Y)O3 Coating Via Sol-Gel Processes for Metal-Supported Protonic Ceramic Fuel Cells

Metal-supported solid oxide fuel cells (MS-SOFCs), a form factor that replaces the ceramic support of conventional anode-supported SOFCs with metal, offer several advantages over ceramic-supported SOFCs, such as enhanced ruggedness against mechanical shock, rapid thermal transients, and redox cycling. Meanwhile, protonic ceramic fuel cells (PCFCs) have attracted attention due to their lower proton-conducting activation energy compared to oxygen ion-conducting activation energy at intermediate temperatures. To further lower the operating temperature of MS-SOFCs, one potential solution is to fabricate metal-supported cells with proton-conducting electrolytes, such as barium zirconate-cerate-based materials. However, using the conventional co-sintering approach is not possible because the required sintering temperature for the densification of the proton-conducting ceramic electrolyte is too high to sustain the porous microstructure of the metal support. Therefore, low-temperature film deposition processes, such as physical vapor deposition or sol-gel coating, are required to fabricate the metal-supported protonic ceramic fuel cells (MS-PCFCs). Additionally, the good step coverage of sol-gel coating is advantageous for depositing thin and gas-tight electrolytes on porous anode surfaces.
In this work, a sol-gel coating process is developed for dense BaZr_0.8Y_0.2O₃ (BZY) coatings at low-temperatures (< 1000 °C) on a porous anode surface. A precipitation-free sol is synthesized by mixing solvent, chelating agent, metal acetates, and alkoxides in a specific order. The sol is spin-coated on a silicon wafer and the porous anode surface of anode-supported or metal-supported cells for X-ray diffraction analysis and microstructure characterizations. It is shown that a crystalline BZY film without secondary phases can be formed by heat treatment above 800 °C. Furthermore, cross-sectional SEM analysis reveals that a thin and crack-free BZY film can be successfully deposited on a porous anode surface at heat treatment temperatures below 1000 °C. The developed coating process can be one of the feasible solutions for successful MS-PCFCs fabrication.