In a significant advancement for fuel cell technology, researchers from Tokyo Tech and Tohoku University have discovered hexagonal perovskite-related oxides, such as Ba5Er2Al2SnO13, with exceptional proton conductivity and thermal stability. These materials offer high proton diffusion, making them ideal electrolytes for next-generation protonic ceramic fuel cells that can operate at intermediate temperatures without degradation. Fuel cells combining hydrogen and oxygen to produce electricity have long been viewed as a clean energy solution. Most fuel cells use solid oxide fuel cells (SOFCs), which face challenges due to high operating temperatures. Protonic ceramic fuel cells (PCFCs) using proton-conducting ceramics are being explored for operation at more manageable temperatures. The researchers' breakthrough involves identifying Ba5Er2Al2SnO13 as a high proton conductor with a conductivity nearly 0.01 S cm-1 at 303 °C, surpassing other proton conductors. The crystal structure and full hydration of the material facilitate fast proton migration, enhancing conductivity. Moreover, simulations revealed long-range proton migrations in the octahedral layers of the material. Notably, Ba5Er2Al2SnO13 displayed chemical stability under PCFC operating conditions, making it a promising candidate for efficient, durable, and lower-temperature fuel cells.