Participation of the unstable lattice oxygen of cation-exchanged δ-MnO in the water oxidation reaction

• Published in: Journal of materials chemistry. A, Materials for energy and sustainability Materials for energy and sustainability, 2023-10, Vol.11 (4), p.21686-21693
• Main Authors: Ham, Kahyun, Kang, Sinwoo, Kim, Yeongin, Lee, Youjin, Kim, Young-Dok, Lee, Jaeyoung
• Format: Article
• ISSN: 2050-7488; 2050-7496
• DOI: 10.1039/d3ta02969g

Among 3d transition metal oxides, Mn oxides function as electrocatalysts for the oxygen evolution reaction (OER) in alkaline media. At the OER potential, some Mn oxides are oxidized to a layered structure birnessite-type δ-MnO 2 , so strategies to improve the OER activity of δ-MnO 2 and elucidate its reaction mechanism have been suggested. Here, we demonstrated for the first time that δ-MnO 2 can follow the lattice oxygen participation mechanism (LOM) rather than the conventional adsorbate evolution mechanism and the contribution of LOM can improve the OER activities of δ-MnO 2 . Consistent with the electrochemical evidence for LOM, we found the isotopic shift of Mn-O and active oxygen in an 18 O-labeling experiment by in situ Raman analysis. The oxygen vacancies introduced by the intercalated cation between MnO 6 layers thermodynamically activate the lattice oxygen of δ-MnO 2 and absorb OH − ions in the alkaline electrolyte, enabling the unstable lattice oxygen to participate in the OER as the reactant. The isotopic shift of the Mn-O bonds in Co 2+ /MnO 2 indicates that the lattice oxygen is replaced by the electrolyte, shifting the OER mechanism to a lattice oxygen participation mechanism.