Iridium Incorporation into MnO2 for an Enhanced Electrocatalytic Oxygen Evolution Reaction

Abstract We 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 MnO 2 , (birnessite, nominally δ‐MnO 2 ) and the 3D MnO 2 (pyrolusite, β‐MnO 2 ). The Ir‐incorporated β‐MnO 2 (Ir/β‐MnO 2 ) electrocatalysts were prepared for the first time via a thermally induced phase transition of δ‐MnO 2 containing 16–22 wt% Ir. This phase transition of δ‐MnO 2 to β‐MnO 2 was facilitated by the presence of Ir in the structure, as both Ir in IrO 2 and Mn in β‐MnO 2 could adopt a thermodynamically favored rutile structure. Extended X‐ray absorption fine structure (EXAFS) of Ir/β‐MnO 2 showed that the catalyst consisted of Ir substituted into the crystalline β‐MnO 2 lattice. 22 wt% Ir/β‐MnO 2 (60 ) exhibited an OER overpotential ( ) of 337 mV, lower than the for commercial IrO 2 . This was constant for 6 h, at 10 mA in 0.5 M H 2 SO 4 . 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‐MnO 2 had a strained structure containing ∼41 % Mn 3+ , an OER active species, along with a modified Ir bond covalency consisting of both Ir−O−Ir and Ir−O−Mn.