Development of glass-ceramic sealants and modeling of single repeating unit for reversible Protonic ceramic cells (PCCs)

Nowadays, one of the key drivers for the energy transition to a low-carbon scenario is the utilization of hydrogen as an energy vector. Its utilization represents a sustainable energy conversion route and a potential storage system for renewable energy sources, to overcome the limit of their intermittent behavior. Hydrogen can be produced by electrolysis of water (green hydrogen) and used as a fuel to generate electricity. High-temperature electrolyzers and fuel cells with ceramic-based electrolytes demonstrate to possess high conversion rates due to the high working temperatures employed. Solid Oxide Cells (SOCs) and Protonic Ceramic Cells (PCCs) work in the ranges 700 – 1000 °C and 400 – 700 °C, respectively. Of the two, SOCs are nowadays the most developed technology, however, their high working temperature range is the primary cause of degradation during operation. In this regard, PCCs, based on a proton-conducting electrolyte, represent a promising candidate for reducing operating temperatures, maintaining high efficiencies and reducing costs. In the upscaling from single PCCs to commercial stacks, an intermediate step is the development of a single repeating unit (SRU). One of the most critical elements in the SRU is the sealant component, which must prevent the mixing of the gases within the stack and electrically insulate the cells. Glass-ceramics materials already proved their feasibility as sealants for SOC applications due to their thermochemical compatibility during operation. Moreover, to ensure the proper functionality of the sealant during operation, its deposition with automatized systems is highly recommended. In the present study, three glass-ceramic systems for application in PCCs operating at two typical operating temperatures (e.g., 550 and 600 °C) are characterized. Their chemical and thermo-mechanical compatibility with the substrates (metallic interconnect and ceramic electrolyte) that will compose the SRU is evaluated in static air. Moreover, the chemical stability and reactivity of the sealants with the interconnect material are evaluated in simulated PCC operating conditions by dual atmosphere test. Here robocasting, which is an extrusion-based additive manufacturing (AM) method is used. Robocasting allows to obtain the reliable and automatic deposition of sealing profiles. Glass pastes are prepared, and optimization of their formulation is performed to reach the correct printability and shape-fidelity for the extrusion process. Moreover, robocasting printing parameters are studied to obtain the required thickness and width of the sealing profiles. Finally, the advances obtained have been exploited to develop a 2D numerical model of a single PCC and a first 3D numerical model of SRU by means of the software COMSOL Multiphysics (COMSOL Group). The models are calibrated by means of literature data and the experimental results from the glass sealant optimization. In the future, the 3D model will be calibrated by using experimental data performed on PCCs. In this way, the model will be validated and will be applied for the optimization of the SRU geometry.