Single‐Atom Ir Reserved in Lower Oxidation State by Divalent Iron for Efficient Alkaline Water Oxidation

Abstract Ir in a lower oxidation state exhibits superior intrinsic activity for oxygen evolution reaction (OER) due to its low Ir‐O connectivity in alkaline media. However, it is more prone to being oxidized to a high oxidation state and dissolving inactivation during the OER process. Herein, single‐atom Ir in a lower oxidation state is dispersed on a sea urchin‐like FeNi‐based spinel support (NiFe ₂ O ₄ ) possessing super‐hydrophilicity and super‐aerophobicity. The as‐prepared Ir/NiFe ₂ O ₄ , loading of only 0.087 mg _Ir cm ⁻² Ir element, shows 196 mV overpotential at 10 mA cm ⁻² , and it can work stably up to 400 h at 200 mA cm ⁻² in 1 m KOH solution. The OER performance of Ir/NiFe ₂ O ₄ surpasses that of commercial IrO ₂ catalysts and most currently reported Ir/Ru‐based single‐atom catalysts (SACs), which can be attributed to Fe ²⁺ in the support acting as an electron reservoir, maintaining the lower oxidation state of single‐atom Ir with high activity and stability during the OER process. Furthermore, the catalytic interface exhibits both super‐hydrophilicity and super‐aerophobicity, which not only facilitates electron‐ion coupling transport but also promotes the rapid removal of generated oxygen bubbles.