Joining the BaZr_0.1Ce_0.7Y_0.1Yb_0.1O_3-δ Electrolyte to AISI 441 Interconnect for Protonic Ceramic Fuel Cell Applications: Interfacial Microstructure and Long-Term Stability

One challenge for the commercialization of protonic ceramic fuel cells (PCFCs) is the lack of sealing technology for fabricating PCFC stacks, while related studies are limited. In this study, the Ag–CuO braze is employed to successfully join the BaZr0.1Ce0.7Y0.1Yb0.1O3-δ (BZCYYb) electrolyte to AISI 441 interconnect for the PCFCs. The wettability of Ag–CuO braze on the BZCYYb surface can be tailored by changing the CuO content. The influence of CuO content and brazing temperature on the joint microstructure is analyzed. Sufficient wettability of the braze and limited interfacial reaction can be achieved using Ag-2 mol % CuO at 970–1000 °C. Under this condition, a reaction layer (Cu2Yb2O5, BaCr2O4) is formed at the BZCYYb interface, and an oxide layer ((Cu, Cr, Fe)3O4, Cr2O3) is observed at the AISI 441 interface. In addition, the long-term stability of as-brazed joints is assessed by aging in both wet oxidizing (50% air–50% H2O) and reducing (4% H2–96% Ar) atmospheres for 300 h at 600 °C. After aging tests, the joints remain intact and dense, indicating that the Ag–CuO braze system is applicable for fabricating PCFC stacks.