Joining of solid oxide fuel/electrolysis cells at low temperature: A novel method to obtain high strength seals already at 300 °C

A novel method using a combination of surface three-dimensional structuring, silver nanoparticles and a silver-foam interlayer is developed for joining solid oxide fuel/electrolysis cell components at low temperature. Joints with a high mechanical strength of 24 MPa are obtained with this method already at 300 °C. The interfaces of a sealed assembly comprising ferritic stainless steel interconnect and nickel oxide-yttria stabilized zirconia (NiO-YSZ) support are analyzed by scanning electron microscopy and transmission electron microscopy to study the interfacial sintering mechanism. It is shown that the high strength of the joint is due to a combination of an optimized three-dimensional nickel/gold nanosheet array deposited on the substrates which facilitates mechanical interlocking, and a silver-foam interlayer which enhances the resistance to crack propagation. The long-term stability of the joint is evaluated by aging in a reducing atmosphere at 800 °C for 250 h. No defects indicating a possible failure are observed in the joint after this aging. An oxide layer forms along the silver/steel interface and parts of the steel are transformed to austenite due to nickel diffusion from the nanosheet array, but this does not deteriorate the joint stability.