Dual‐Phase Reaction Sintering for Overcoming the Inherent Sintering Ability of Refractory Electrolytes in Protonic Ceramic Cells

Abstract The proton‐conducting oxides, widely employed as electrolytes in ceramic electrochemical cells, exhibit remarkable proton conductivity that facilitates efficient energy conversion processes. However, their inherent refractory nature poses a challenge in producing chemically stoichiometric and physically dense electrolytes within devices. Here a novel approach is presented, dual‐phase reaction sintering, which can overcome the inherent low sintering ability of the representative BaCeO 3‐δ ‒BaZrO 3‐δ proton conducting oxides. This approach involves the simultaneous transformation of a two‐phase mixture (comprising fast‐sintering and slow‐sintering phases) into a complete single‐phase solid solution compound, along with the densification of the electrolyte, all accomplished within a single‐step heating cycle. During the dual‐phase reaction sintering process, the grains of the fast‐sintering phase experience rapid growth owing to their intrinsic superior sintering ability. Additionally, this growth is augmented by the Ostwald ripening behavior manifested by the smaller slow‐sintering phase. This synergistic strategy is validated using BaCe 0.4 Zr 0.4 Y 0.1 Yb 0.1 O 3‐δ , and its applicability in electrochemical cells is demonstrated, resulting in a significant enhancement in performance. These findings offer insights into streamlining the preparation of refractory ion‐conducting ceramic electrolytes while maintaining their intrinsic properties for practical applications.