Iridium Incorporation into MnO 2 for an Enhanced Electrocatalytic Oxygen Evolution Reaction

• Published in: ChemCatChem Vol. 15; no. 8
• Main Authors: Kakati, Uddipana, Elzinga, Evert J., Mansley, Zachary R., Roe, Benjamin, Alimohammadi, Farbod, Schwenk, Gregory, Ning, Jinliang, Zhu, Yimei, Ji, Hai‐Feng, Sun, Jianwei, Strongin, Daniel R.
• Format: Journal Article
• Language: English
• Published: Germany Wiley Blackwell (John Wiley & Sons) 21.04.2023
• ISSN: 1867-3880; 1867-3899
• DOI: 10.1002/cctc.202201549

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.