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

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_0.4Zr_0.4Y_0.1Yb_0.1O_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.