Advancements in glass-ceramic sealants for Proton Conductive Ceramic Electrolysis Cells (PCCECs)

Nowadays, the danger represented by the utilization of greenhouse gases shifted the global energy scenario towards renewable energies such as solar, wind, tide, etc. Despite the global need for a green transition many efforts are necessary, mostly due to the intrinsic intermittent nature of renewable sources. Among different energy carriers, hydrogen is particularly promising as vector. Its application proposes a sustainable energy conversion pathway as well as a potential storage solution for renewable energy sources. Hydrogen can be produced by water electrolysis (i.e., green hydrogen) with low-carbon emissions. The most efficient electrolysis cells to produce green hydrogen are high temperature electrolysis cells (HTEs). Solid oxide electrolysis cells (SOECs) and protonic ceramic electrolysis cells (PCECs) operate at temperatures ranging from 700 to 1000 °C and 400 to 700 °C, respectively. Because of the high working temperatures used, HTEs with ceramic-based electrolytes exhibit high conversion rates. SOECs are the most advanced of the two technologies. However, SOECs are prone to degradation due to the high working temperature range. In addition, the high temperatures mean a relevant cost for their utilization. In this sense, PCECs based on a proton-conducting ceramic electrolyte are good candidates to lower the operating temperatures, maintaining high efficiencies, and cutting costs. Due to difficulties with the sintering of the materials used for PCECS production and to the compatibility with the other elements of an SRU, PCECs are now primarily at the laboratory size. The upscaling to commercial stacks involves first to develop a so-call single repeating unit (SRU). The purpose of this thesis is to advance understanding of this unresolved issue, with a focus on the characterization of the sealant material. The sealant is an important component in this technology because it inhibits gas leakage or diffusion within the stack. In the present investigation, glass-ceramic sealants were considered. The characterization process included both thermomechanical and chemical aspects of the sealant material, such as compatibility with the other components of a stack of cells (electrolyte, electrode, and interconnector), as well as the behavior of the chosen material at the operational temperature (400-700°C). Here, robocasting, an extrusion-based additive manufacturing (AM) process, is applied. Robocasting enables the reliable and automated deposition of sealing profiles, which would lay the groundwork for industrial scaling of production. Glass pastes are prepared, and their formulation is optimized to achieve the desired printability and shape fidelity for the extrusion process. Furthermore, robocasting printing parameters are being studied to determine the necessary thickness and width of the sealing profiles.