Low‐Ir‐Content Ir0.10Mn0.90O₂ Solid Solution for Highly Active Oxygen Evolution in Acid Media

Iridium (Ir)‐based materials are the most widely used oxygen evolution reaction (OER) electrocatalysts in proton exchange membrane water electrolysis (PEMWE). However, their commercial application suffers from high cost and insufficient activity. To optimize the atom utilization efficiency of Ir, the aim is to engineer and develop a rutile‐structured solid solution catalyst with minimal Ir content, which is identified through a phase boundary. Here, Ir 0.10 Mn 0.90 O 2 represents the lowest Ir content in the desired IrO 2 ‐MnO 2 solid solution. The Ir 0.10 Mn 0.90 O 2 catalyst exhibits outstanding OER performance in acidic electrolytes, reaching a remarkable mass activity of 1135 A g −1 Ir at an overpotential of 300 mV, which is ≈50 times higher than that of a commercial IrO 2 catalyst. Additionally, it demonstrates excellent stability at a current density of 200 mA cm −2 over 120 h during PEMWE operations. Density functional theory (DFT) calculations indicate that the hydroxylation process can be efficiently promoted by the electron‐withdrawing on Ir sites in Ir 0.10 Mn 0.90 O 2 , contributing to the enhancement of OER activity.