Multiscale interface engineering via femtosecond laser synergized with micro-Ag interlayer for robust ceramic-metal sintered-joining in protonic ceramic fuel cells

Reliable ceramic-metal joining is essential for the construction of protonic ceramic fuel cell (PCFC) stacks, yet joint failure still occurs on the electrolyte ceramic side. For the first time, this study proposes a femtosecond laser-enabled multiscale interface engineering strategy to promote the sintered-joining between BaZr_0.4Ce_0.4Y_0.1Yb_0.1O_3-δ electrolyte and Crofer 22 APU interconnect. The method enables the formation of microscale grooves (15 μm width and 2.5 μm depth), nanoscale clusters (ranging from several tens to hundreds of nanometers), and oxygen vacancies (concentration increased by 100 %) at a laser power of 12 mW. The resulting hierarchical interface architecture markedly promotes effective sintering of the micro-Ag particle interlayer. Under optimized conditions (930 °C, 1 MPa, 30 min), the resulting joints are defect-free and exhibit exceptional durability in humid oxidative environments. The shear strength reaches 42.8 MPa, representing a 97 % improvement over untreated samples. The multiscale enhancement mechanism is systematically elucidated. First-principles calculations further reveal a novel atomic-scale joining mechanism: laser-induced oxygen vacancies trigger localized Jahn-Teller distortion of the crystal field, thereby enhancing the d-p orbital hybridization between the coordinating O and Ag. This femtosecond laser-driven interface engineering strategy offers a robust and scalable solution for high-performance ceramic-metal integration in advanced energy systems.