AbstractWe have investigated the structure and activity of electrocatalysts for the oxygen evolution reaction (OER) that had low loadings of Ir incorporated into the 2D layered MnO₂, (birnessite, nominally δ‐MnO₂) and the 3D MnO₂ (pyrolusite, β‐MnO₂). The Ir‐incorporated β‐MnO₂ (Ir/β‐MnO₂) electrocatalysts were prepared for the first time via a thermally induced phase transition of δ‐MnO₂ containing 16–22 wt% Ir. This phase transition of δ‐MnO₂ to β‐MnO₂ was facilitated by the presence of Ir in the structure, as both Ir in IrO₂ and Mn in β‐MnO₂ could adopt a thermodynamically favored rutile structure. Extended X‐ray absorption fine structure (EXAFS) of Ir/β‐MnO₂ showed that the catalyst consisted of Ir substituted into the crystalline β‐MnO₂ lattice. 22 wt% Ir/β‐MnO₂ (60 ) exhibited an OER overpotential ( ) of 337 mV, lower than the for commercial IrO₂. This was constant for 6 h, at 10 mA in 0.5 M H₂SO₄. EXAFS, high‐angle annular dark‐field scanning transmission electron microscopy (HAADF‐STEM) and X‐ray absorption near edge structure (XANES) showed that 22 wt% Ir/β‐MnO₂ had a strained structure containing ∼41 % Mn³⁺, an OER active species, along with a modified Ir bond covalency consisting of both Ir−O−Ir and Ir−O−Mn.