Innovative glass sealants for the integration of protonic ceramic electrolysis cells

This work reports the design, processing, and testing of novel borate-based glass sealants for joining ferritic stainless steel AISI 441 interconnects to NiO-SrZr 0.5 Ce 0.4 Y 0.1 O 3-δ (SZCY541)/BaZr 0.44 Ce 0.36 Y 0.2 O 3-δ (BZCY442) protonic half-cells. Two formulations, belonging to the B 2 O 3 –BaO–Al 2 O 3 –CaO–SrO–SiO 2 and B 2 O 3 –BaO–SiO 2 –Al 2 O 3 –CaO–SrO–ZnO–ZrO 2 systems, are tailored to enable low-temperature joining (<700 °C), thereby limiting interfacial reactivity while ensuring thermomechanical compliance at operating temperatures ( ≈ 600 °C). The effects of glass chemistry and powder morphology on densification, viscous flow, and crystallisation are systematically investigated, showing predominantly surface-controlled crystallisation behaviour. Screen-printed tapes are used to fabricate symmetric metal/glass/metal assemblies. The joining process is optimised by varying peak temperature and applied pressure to correlate sealant deformation and gas-tightness with processing conditions, defining reliable joining parameters for PCEC stack integration. The resulting samples show excellent sealing performance, with He leakage rates below 1 × 10 −9 mbar L s −1 and a final sealant thickness of ≈ 200 μm. Optimised conditions are applied to half-cell/glass/metal joined samples, exhibiting gas-tightness (Δp < 2 mbar after 5 min) and stable geometry. SEM–EDS confirms strong adhesion and chemical compatibility with NiO–SZCY541/BZCY442 and AISI 441, demonstrating the suitability of the investigated compositions for PCEC sealing.