Unraveling the Enhanced Kinetics of Sr₂Fe_1+xMo_1‐xO_6‐δ Electrocatalysts for High‐Performance Solid Oxide Cells

Abstract The performance of Sr₂FeMoO_6–σ double perovskites can be significantly enhanced by optimizing the ratio of Fe/Mo as a promising electrode material for solid oxide fuel/electrolysis cells. However, the intrinsic origin is still doubt for the improvement of Sr₂FeMoO_6–σ sluggish electrocatalytic reaction kinetics. Herein, their electronic structures are investigated by partial replacement of Mo with Fe ions. As the Fe content in Sr₂Fe_1+xMo_1–xO_6–δ is increased, its oxidation state increases, which enhances the metal–oxygen hybridization and shifts its bulk O p band energy toward the Fermi level. These electronic and structural variations decrease the O‐vacancy formation and migration energy, which, in turn, facilitates the formation of more oxygen vacancy defects and O ion transport, promoting the full contact between analytes and active B‐site transition metals and also the catalytic reaction kinetics. Consequently, the solid oxide cells with optimized Sr₂Fe_1.5Mo_0.5O_6–σ electrodes operating at 800 °C demonstrate high power density of 1.24 W cm⁻² using H₂ as fuel, and large CO₂ electrolysis current density of 1.5 A cm⁻² at 1.5 V, which are comparable with those of current state‐of‐the‐art Ni‐based catalysts. The findings provide a new understanding for the origin of the enhanced reaction kinetics of Sr₂Fe_1+xMo_1–xO_6–δ serial materials by increasing Fe doping.