High-Entropy Lithium-Ion Electrolyte Enabled High-Performance Composite Proton Conductor

The BaZr_0.1Ce_0.7Y_0.2O_3-δ (BZCY) series dominates proton conductor research owing to its competitive proton conductivity, yet its high sintering temperatures induce barium volatilization and irreversible degradation in conductivity. Herein, we report a high-performance composite proton conductor comprising a high-entropy lithium-ion (Li⁺) conducting electrolyte and BZCY, fabricated via ultrafast high-temperature sintering (UHS). Incorporating the high-entropy Li⁺ conductor Li_6.5LaPrNdZr_0.75Ce_0.75Ta_0.5O₁₂ (HE-PNC) enabled rapid densification and effective connection of BZCY grains at lower temperatures. This allows sintering at a significantly lower temperature (960 °C) compared to conventional methods (1400 °C), effectively suppressing barium volatilization at higher temperatures. The continuous, soft-phase framework formed by HE-PNC enables conformal interfacial contact with the uniformly dispersed BZCY particles. This intimate contact creates new, efficient proton transport pathways along the HE-PNC/BZCY interfaces, allowing protons to bypass the sharp grain boundaries of BZCY and thereby accelerating overall proton transport across the material. Consequently, the composite proton conductor exhibits superior proton conductivities as high as 36, 98, and 195 mS cm^-1 under a wet H₂ atmosphere at 450, 600, and 800 °C, respectively. This research advance enables concurrent optimization of electrolyte processing conditions (ΔT_sinter = 440 °C reduction) and the operational temperatures of proton conductor ceramic fuel cells, establishing a new pathway for practical proton conductor ceramic fuel cell systems.