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 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 (Formula presented.)) exhibited an OER overpotential ((Formula presented.)) of 337 mV, lower than the (Formula presented.) for commercial IrO2. This (Formula presented.) was constant for 6 h, at 10 mA (Formula presented.) 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.
All Science Journal Classification (ASJC) codes
- Physical and Theoretical Chemistry
- Organic Chemistry
- Inorganic Chemistry
- iridium oxide
- manganese oxide
- oxygen evolution reaction