Synthesis of Yttrium Doped Barium Zirconate/Cerate Electrolyte Materials and Densification Using Conventional and Cold-Sintering Processes

Compared to high temperature SOEC usually based on Yttrium stabilized Zirconia electrolytes, intermediate temperature PCEC allows the production of water free hydrogen and a better chemical stability. Proton conducting perovskite specific materials, such as Barium Indates 1 , Zirconate or Cerates 2 are nearly commercial electrolytes for such devices. This study focuses on the synthesis the characterization and the densification of the BaZr 1-x Ce x Y 0.1 O 3- δ 3 powder. At intermediate temperature and under humid atmosphere, hydration process allows diffusion of protonic charges. Such electrolyte material combines a low thermal expansion coefficient and a high protonic conductivity. Two specific stoichiometry’s have been studied, Cerium rich BaZr 0.3 Ce 0.6 Y 0.1 O 3- δ (BZCY361) and Zirconium rich BaZr 0.7 Ce 0.2 Y 0.1 O 3- δ (BZCY721). BZCY361 shows at 550°C, a conductivity level of 2.10 - 2 S.cm - 1 . However, despite its high protonic conductivity, the cerium rich phase is not stable at high temperature and is torn apart in presence of carbon dioxide. BaZr 1-x Ce x Y 0.1 O 3- δ powder has been synthetized by combustion reaction based on nitrate precursors and glycine as organic complexing/fuel agent. The fuel/oxidizer (nitrates) ratio, which is a key parameter 4 , has been optimized in order to obtain the best purity and crystallinity. The powder is then milled and calcined. The single-phase electrolyte powder is conventionally shaped into pellets and densified A minimal temperature of 1600°C is necessary to obtained a density of 90-95%. In order to reduce the sintering temperature, an intermediate sintering step called "Cold Sintering Process" 5 (CSP) has been investigated. In this technic, derived from the hydrothermal method, BCZY powder mixed with a small volume of liquid phase (3-30 wt%) is simultaneously pressed (at 50 to 500 MPa) and heated during a short time period (1-60 min) at low temperatures (100-200°C), leading to dense pellets. In regards to design a complete cell based on this electrolyte, EIS has been performed under hydrogen and air atmosphere. The electrochemical measurements of the samples provided by the different protocols and stoichiometry’s have been compared in order to determine the impact of the CSP and stoichiometry parameters on the ionic conductivity of the material. Acknowledgment: This study, included in the PhD of P. Castellani, was made possible with support from the Franco German ANR-BMBF project (Grant No. ANR-19-ENER-0003-12 [1] Quarez, Eric, Samuel Noirault, Annie Le Gal La Salle, Philippe Stevens, et Olivier Joubert. « Evaluation of Ba 2 (In 0.8 Ti 0.2 ) 2 O 5.2−n (OH) 2n as a Potential Electrolyte Material for Proton-Conducting Solid Oxide Fuel Cell ». Journal of Power Sources 195 (15), 4923-27 (2010) [2] Thabet, K., Le Gal La Salle, A., Quarez, E., and Joubert, O. “Protonic-Based Ceramics for Fuel Cells and Electrolyzers,” Solid Oxide-Based Electrochemical Devices , Elsevier, pp. 91–122 (2020) [3] Thabet, K., Devisse, M., Quarez, E., Joubert, O., and Le Gal La Salle, A. “Influence of the Autocombustion Synthesis Conditions and the Calcination Temperature on the Microstructure and Electrochemical Properties of BaCe 0.8 Zr 0.1 Y 0.1 O 3− δ Electrolyte Material,” Solid State Ionics, 325 , pp. 48–56, (2018) [4] Varma, A., Mukasyan, A. S., Rogachev, A. S., and Manukyan, K. V., “Solution Combustion Synthesis of Nanoscale Materials,” Chem. Rev., 116 (23), pp. 14493–14586 (2016) [5] Guo, H., Baker, A., Guo, J., and Randall, C. A., “Cold Sintering Process: A Novel Technique for Low‐Temperature Ceramic Processing of Ferroelectrics,” J. Am. Ceram. Soc., 99 (11), pp. 3489–3507 (2016) Figure 1