Unraveling the Enhanced Kinetics of Sr2Fe1+xMo1‐xO6‐δ Electrocatalysts for High‐Performance Solid Oxide Cells

The performance of Sr2FeMoO6–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 Sr2FeMoO6–σ sluggish electrocatalytic reaction kinetics. Herein, their electronic structures are investigated by partial replacement of Mo with Fe ions. As the Fe content in Sr2Fe1+xMo1–xO6–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 Sr2Fe1.5Mo0.5O6–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 Sr2Fe1+xMo1–xO6–δ serial materials by increasing Fe doping. Partial substitution of Mo by Fe in perovskite of Sr2Fe1+xMo1‐xO6‐δ enhances the metal–oxygen hybridization and shifts up the O p band energy closer to Fermi level, which results in lower O vacancy formation as well as a lower O migration barrier energy, significantly accelerating their catalytic reaction kinetics in H2 oxidation and CO2 reduction reactions in solid oxide cells.