Formulation of novel glass sealants for Protonic Ceramic Cells (PCCs) applications

Nowadays, the global energy scenario is undergoing a remarkable shift as the world endeavours to cut greenhouse gas emissions by transitioning to more sustainable energy sources. Within this framework, hydrogen has emerged as an important energy vector for decarbonisation, being a potential storage for renewable energy systems. In recent years, green hydrogen produced by water electrolysis with reversible electrochemical devices demonstrated to be a feasible way to reduce emissions. Among many electrochemical devices, high-temperature electrolysers and fuel cells with ceramic-based electrolytes demonstrated to provide high conversion rates and efficiency. According to the electrolyte material and the ionic conduction mechanism, ceramic-based cells are classified into solid oxide fuel cells (SOC) and proton conducting cells (PCC). Nowadays, SOCs are the most mature technology, however, due to the high??temperature level required to enhance the charge transport the lifespan of the cell is strictly limited by the degradation phenomena. In this regard, PCCs, based on a proton-conducting electrolyte, are a promising candidate for reducing operating temperatures, maintaining high-efficiency levels and reducing costs. Currently, PCCs feature a technology readiness level (TRL) of 3, and only a few reports are focused on the upscaling from single cell to commercial stacks. One of the most critical aspects that have to be studied is the sealing of an integrated system, such as a single repeating unit (SRU) or a stack of cells. Glass-ceramics materials are under investigation as a possible sealant of PCCs as their thermo-mechanical compatibility and chemical stability have been already proven in SOCs. In the present study, two barium-borate-silica glass compositions have been formulated and investigated as glass sealants for PCC. The glasses have been formulated to work in an intermediate temperature range i.e., 500°C-650°C. Aiming to study the thermomechanical properties of the glasses, different analyses such as differential scanning calorimetry (DSC), dilatometry (DIL) and heating stage microscopy (HSM), have been performed. Subsequently, to study the compatibility of the formulated glasses with two types of proton ceramic electrolytes, i.e., BCZYYb and BZY20 and with two typical ferritic stainless steels used as interconnects, i.e., Crofer22APU and AISI441, joined samples have been produced. To study the compatibility of the sealant, the joined samples will be analysed after the joining procedure, after ageing performed with different atmospheres (static air and air + steam). The joined samples have been characterized by SEM-EDX and XRD to assess the good compatibility at both interfaces.