An Active Catalyst for Efficient High‐Temperature Water Splitting on Oxygen‐Ion‐Based Solid Oxide Electrolysis Cells

High‐temperature solid oxide electrolysis cells (SOECs) with oxygen‐ion‐conducting electrolytes are highly efficient devices for hydrogen production via water splitting, but currently face significant challenges related to the insufficient catalytic activity and poor stability of the fuel electrode. In this work, the design of Ni‐Zr 0.84 Y 0.16 O 2−δ (YSZ) fuel electrodes modified by a surface catalyst of Pr 0.975 Sm 0.025 O 2‐δ (PSO) nanoparticles are reported, demonstrating significantly enhanced catalytic activity and durability toward water splitting for hydrogen production. The improved catalytic activity and reaction rate can be attributed to the presence of the Pr 3+ /Pr 4+ redox couple and the high concentration of oxygen vacancies, as confirmed by the X‐ray photoelectron spectroscopy, electrochemical impedance spectroscopy, and corresponding distribution of relaxation times analysis. Specifically, a single cell with the PSO catalyst‐coated Ni‐YSZ fuel electrode delivers an impressive peak power density of 1.27 W cm −2 in fuel cell mode, current density of −1.31 A cm −2 at 1.3 V, and excellent operating stabilities at −0.5 A cm −2 for over 200 h at 700 °C for water splitting (50% H 2 O). Moreover, a hydrogen production rate of 3.48 mL min −1 cm −2 at −0.5 A cm −2 and nearly 100% Faradaic efficiency are achieved at 700 °C.