Protonic ceramic electrolysis cells (PCECs) are high-temperature electrolysis cells where the solid electrolyte is a proton-conductive ceramic characterized by high conductivity (I. Zvonareva et al., Energy Environ. Sci., 2022). If compared with traditional solid oxide electrolysis cells (SOECs), where oxygen-conductive materials are used as the electrolyte, PCECs present two important advantages. Firstly, they operate at a considerably lower temperature range (700-900 °C and 400-600 °C for SOEC and PCEC, respectively). Secondly, in a PCEC, steam is provided at the oxygen electrode, meaning that at the fuel electrode, pure hydrogen can be produced.
As in the case of SOEC, the operation of a PCEC requires gas tightness between the oxygen and the fuel electrodes. In this sense, the utilization of glass-ceramic materials as sealants has been demonstrated as an excellent solution for the scale-up of SOEC and the staking of large-area cells (I. Ritucci, et al., J. Mater. Res., 2019). Nowadays, no studies have been found related to the compatibility between SoA PCEC materials and glass-ceramic sealants. Moreover, the scale-up of this technology is still under development as only a few studies report PCEC operations beyond the lab-scale level (L. Q. Le, et al., Journal of Power Sources, 2021).
In both SOEC and PCEC devices, the good performance of glass-ceramic composites as sealant is also influenced by the homogeneity of the layer and the control of its thickness. The utilization of automatized systems for the deposition of sealants is highly recommended to ensure such homogeneity. In particular, additive manufacturing techniques (e.g., robocasting) proved to be particularly effective for this task (S. Lamnini, et al., Materials Letters, 2022).
This work aims to fill the gap related to glass-ceramic sealants for PCEC applications. To pursue this goal, the results of three Si-based glass ceramic materials joined with Ba(Ce,Zr)_1-yY_yO_3-δ (BCZY), an SoA electrolyte for PCEC, are presented. Glass-ceramic compositions have been specifically formulated for this application and their thermochemical compatibility has been studied with the BCZY electrolyte material. Moreover, the compatibility of the formulated glass-ceramic sealants has been studied with the typical ferritic stainless steels (FSSs) used as interconnect in SOEC (i.e., Crofer22APU and AISI441). A complete characterization by DTA, dilatometry, hot stage microscopy (HSM), FESEM and XRD have been performed on the glass-ceramic powders and on the joined samples FSS/glass-ceramic/electrolyte. Additionally, glass-ceramic-based pastes have been formulated for the automatized deposition of sealants by robocasting and the characterization of their rheological and printability properties have been performed. Finally, the deposited sealants have been electrochemically characterized with the application of a voltage and under the application of different gases. This was done to study the compatibility of glass-ceramic composites with PCEC and interconnect materials in real conditions.