Small 2025 Jun 08;2124:e2503136. doi: 10.1002/smll.202503136.

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

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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 (NiFe2O4) possessing super-hydrophilicity and super-aerophobicity. The as-prepared Ir/NiFe2O4, loading of only 0.087 mgIr 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/NiFe2O4 surpasses that of commercial IrO2 catalysts and most currently reported Ir/Ru-based single-atom catalysts (SACs), which can be attributed to Fe2+ 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.

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