Protonic　ceramic　fuel　cells　(PCFCs)　are　promising　for　efficient,　clean　energy　conversion　at　low　to　intermediate　temperatures,　but　the　widely　used　BaZr0.1Ce0.7Y0.1Yb0.1O3-delta　(BZCYYb)　electrolyte　has　poor　chemical　stability　in　humid　environments.　Herein,　we　show　that　under　oxygen　reduction　reaction　(ORR)　conditions,　water　accumulates　at　the　BaGd0.8La0.2Co2O6-delta　(BGLC)　cathode-BZCYYb　electrolyte　interface,　causing　selective　loss　of　Ba　cations　and　decomposition　of　BZCYYb　electrolyte.　The　introduction　of　triply　ion-electron　conducting　La2Ce2O7-delta　(LCeO)　into　the　BGLC　cathode　expands　its　active　reaction　area,　accelerates　ORR　kinetics,　and　suppresses　water　accumulation　at　the　cathode-electrolyte　interface　and　electrolyte　decomposition.　A　single　cell　with　the　BGLC-LCeO　composite　cathode　achieves　a　peak　power　density　of　1.07　W　cm(-2)　at　700　degrees　C,　with　no　profound　degradation　at　0.5　A　cm(-2)　over　100　h.　These　findings　provide　guidance　for　the　development　of　high-performance,　durable　PCFCs.