Hybrid‐Scale Powder Engineering Enables High‐Performance, Durable, and Scalable Protonic Ceramic Electrochemical Cells

Protonic ceramic electrochemical cells (PCCs) offer an efficient pathway for electricity–hydrogen interconversion at intermediate temperatures, yet their practical deployment is hindered by complex fabrication routes and limited scalability. Here, we report a powder‐to‐cell engineering strategy that directly links electrolyte precursor design to cell‐level performance. A hybrid‐scale BaCe 0.7 Zr 0.1 Y 0.1 Yb 0.1 O 3‐δ (BCZYYb) precursor, integrating microscale BaCO 3 with nanoscale metal oxides, enables reaction‐assisted sintering that improves electrolyte densification, suppresses cation segregation, and promotes proton transport. Cells fabricated from this hybrid‐scale powder deliver ∼60% higher power densities than those prepared from fully nanoscale precursors. Importantly, the hybrid‐scale powder can be synthesized at the kilogram scale and is compatible with cost‐effective ceramic processing, enabling the fabrication of large‐area single cells via tape casting, lamination, and co‐sintering. These scaled‐up PCCs exhibit high electrochemical performance and stable steam electrolysis operation at current densities up to 1 A cm − 2 , with a low degradation rate of 0.8% kh − 1 .