Research has been focused on regulating the amorphous surface of Ir-based materials to achieve a higher oxygen evolution reaction (OER) activity. The IrO x amorphous layer is generally considered to be substantial enough to break the limitation created by the conventional adsorbate evolution mechanism (AEM) in acidic media. In this work, we used lanthanides to regulate IrO x amorphization–crystallization through inhibiting the crystallization of iridium atoms in the calcination process. The chosen route created abundant crystalline–amorphous (c-a) interfaces, which greatly enhanced the charge transfer kinetics and the stability of the materials. The mass activity of iridium in the synthesized IrO2@LuIr1–n O x (OH) y structure reached 128.3 A/gIr, which is 14.6-fold that of the benchmark IrO2. All the IrO2@LnIr1–n O x (OH) y (Ln = La–Lu) structures reflected 290–300 mV of overpotential at 10 mA/cmgeo 2. We demonstrate that a highly active c-a interface possesses an efficient charge transfer capability and is conducive to the stability of the activated oxygen species. The surface-activated oxygen species and the tensile strain IrO6 octahedron regulated by lanthanides are synergistically beneficial for increasing the intrinsic OER activity. Our research findings introduce c-a interface generation by the regulation of lanthanides as a new method for the rational design of robust OER catalysts.