Glass sealant for proton conductive membranes

Nowadays, the global energy transition is driven by efforts to cut greenhouse gas emissions and adopt sustainable sources. In this context, hydrogen has emerged as a key energy vector, providing a viable solution for energy storage and helping to mitigate the intermittent nature of renewable sources. Among its production methods, water electrolysis stands out as a carbon-free process, while high-temperature ceramic-based electrolysers and fuel cells offer high efficiency, making them a promising technology for sustainable energy systems. Among these high-temperature electrochemical devices, Solid Oxide Cells (SOCs) and Protonic Ceramic Cells (PCCs) are particularly promising. While SOCs represent the most mature technology, their high operating temperatures (700–1000°C) accelerate degradation, limiting long-term performance. In contrast, PCCs, utilizing proton-conducting electrolytes, offer a promising alternative by enabling lower operating temperatures (400–700°C) while maintaining high efficiency and reducing costs. However, further research is needed to advance PCC technology, particularly in scaling up from single cells to commercial stacks and ensuring the thermomechanical and chemical compatibility of its different components. This study aims to explore and assess the thermomechanical and chemical compatibility of various barium-borate-silica glass sealants with different compositions of proton-conducting membranes. In the first part, the suitability of three glass sealant compositions is discussed, focusing on their thermomechanical properties and compatibility with PCC stack materials. The glass sealants were developed using SciGlass software, optimizing precursor concentrations to ensure thermomechanical and chemical compatibility with the metallic interconnector and perovskite pellet. The study examines the interactions between the sealing glass and the two ceramic materials, as well as with AISI 441 FSS, under different conditions, to assess their compatibility after the joining process. Samples were analysed both after the joining process and following multiple thermal cycles in air/steam environments. X-ray diffraction (XRD) is used to identify potential crystalline phases developed within the sealant, while scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) provide micrographs and elemental maps to assess morphology and diffusion phenomena. A commercial glass is also used to create joints with laboratory-sintered perovskite pellets and AISI 441 FSS. These joined samples are studied, to assess and evaluate their morphology and diffusion behaviour, under three different conditions: as-joined, after thermal aging, and after multiple thermal cycles in air/steam environments. Additionally, using the previously cast glass, pastes were formulated by altering components such as dispersants and binders, along with their concentrations, to achieve the desired rheological properties, with the aim of investigate the feasibility of deposition using a robocasting instrument. Post-deposition properties, including geometry and shape retention, were evaluated using profilometry and image analysis. Beyond the study on PCC glass sealants, a qualitative reliability evaluation of the SciGlass software predictions for different glass compositions was performed using a Design of Experiments (DOE) approach to map the trend of properties, such as the CTE. The differences between experimental results and software predictions are highlighted throughout the text.