Self-supported Iridium Integrated Leaf-Shaped Fe3O4 Columnar Arrays Toward Highly Efficient Oxygen Evolution at Industrial-Grade Current Density

•Leaf-like Fe3O4 nanosheet arrays with rich Fe2+ and oxygen defects are formed.•Ir-Fe3O4/IF-T-x is formed via galvanic replacement between IrCl62− ions and Fe2+.•Ir-Fe3O4/IF-400-2 delivers a low overpotential of 316 mV at 500 mA cm−2 for OER.•The catalyst shows a good long-term stability after 36 h V-t test at 100 mA cm−2.