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-SrZr0.5Ce0.4Y0.1O3-δ (SZCY541)/BaZr0.44Ce0.36Y0.2O3-δ (BZCY442) protonic half-cells. Two formulations, belonging to the B2O3–BaO–Al2O3–CaO–SrO–SiO2 and B2O3–BaO–SiO2–Al2O3–CaO–SrO–ZnO–ZrO2 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.