A novel Ag based sealant for solid oxide cells with a fully tunable thermal expansion

In this work, we show that a promising sealant for the use in solid oxide fuel cell and electrolysis stacks can be obtained by combing a conventional silver-based braze with eucryptite (LiAlSiO₄), a negative thermal expansion coefficient material. The thermo-mechanical properties of the Ag2CuO-LiAlSiO₄ system and the microstructure as a function of the LiAlSiO₄ content are investigated. By adding 8 wt% of the LiAlSiO₄ filler, the coefficient of thermal expansion of the Ag2CuO braze is lowered from 19.6 × 10⁻⁶ K⁻¹ to 12.2 × 10⁻⁶ K⁻¹ (25–800 °C). The aluminized Crofer 22 H is brazed to the gadolinium-dope ceria electrolyte of the solid oxide cell by employing the composite braze. The obtained joints are defect free and display low leak rates (1.2–1.4 × 10⁻³ sccm cm⁻¹). The leak rate and structural integrity of the joints are retained after aging tests at 800 °C for 300 h, indicating excellent stability of the sealant.