Sequential Core–Shell to Alloy Evolution Enables the Structural Stabilization and Catalytic Activation of Solid Oxide Electrolysis Cells

Abstract Solid oxide electrolysis cells (SOECs) offer high efficiency and scalability in green hydrogen production. However, improving their electrochemical performance within conventional fabrication processes is limited because of the substantial structural changes that occur during high‐temperature sintering and the subsequent reduction of the fuel electrode. Herein, sintering‐resistant and spontaneously alloyed NiO@CoO core–shell catalysts fabricated by powder atomic layer deposition (ALD) are presented. The conformal CoO shell suppresses NiO coarsening during sintering, thereby enlarging the triple phase boundary network in the fuel electrode. During subsequent reduction, the core–shell structure spontaneously transforms into a homogeneous NiCo alloy without an additional post‐processing step, enhancing the catalytic activity for the hydrogen evolution reaction. As a result, the ALD‐modified cell exhibits a ≈2 times higher current density of 2.30 A cm −2 at 1.3 V and 750 °C compared to the reference cell. This sequential structural stabilization and catalytic activation within a single fabrication process offers a practical and scalable pathway for realizing high‐performance SOECs.