Constructing Active Sites from Atomic‐Scale Geometrical Engineering in Spinel Oxide Solid Solutions for Efficient and Robust Oxygen Evolution Reaction Electrocatalysts

Abstract Spinel oxides are considered as promising low‐cost non‐precious metal electrocatalysts for oxygen evolution reaction (OER) due to their desirable catalytic activities and fast kinetics. However, as a result of the structural complexity of spinel oxides, systematic and in‐depth studies on enhancing the OER performance of spinel oxides remain inadequate. In particular, the construction of active sites regarding the large number of unoccupied octahedral interstices has not yet been explored. Herein, more octahedral sites with high OER activities are constructed on the surface of spinel oxides via a cationic misalignment, which is induced by the defects in the spinel oxide solutions, i.e., MoFe 2 O 4 and CoFe 2 O 4 nanosheets supported on an iron foam (MCFO NS/IF). With increased active sites and modified electronic structure, the state‐of‐the‐art electrocatalyst exhibits the excellent OER catalytic activity with an onset potential of 1.41 V versus RHE and an overpotential of 290 mV to achieve a current density of 500 mA cm −2 . Moreover, such an electrocatalyst also demonstrates fast kinetics with the Tafel slope of 38 mV dec −1 and superior durability by maintaining the OER activity at 250 mA cm −2 for 1000 h.