Physics

Electrode

Organic chemistry

Crystallography

XANES

Optics

Extended X-ray absorption fine structure

Astronomy

Oxygen evolution

HOMO/LUMO

Absorption spectroscopy

Catalysis

Physical chemistry

Comproportionation

Inorganic chemistry

Chemistry

Molecule

Raman spectroscopy

Spectral line

Quantum mechanics

Electrochemistry

Manganese

Biochemistry

Photochemistry

Proceedings of the National Academy of Sciences

Electrodeposited manganese oxide films are promising catalysts for promoting the oxygen evolution reaction (OER), especially in acidic solutions. The activity of these catalysts is known to be enhanced by the introduction of Mn3+ We present in situ electrochemical and X-ray absorption spectroscopic studies, which reveal that Mn3+ may be introduced into MnO2 by an electrochemically induced comproportionation reaction with Mn2+ and that Mn3+ persists in OER active films. Extended X-ray absorption fine structure (EXAFS) spectra of the Mn3+-activated films indicate a decrease in the Mn-O coordination number, and Raman microspectroscopy reveals the presence of distorted Mn-O environments. Computational studies show that Mn3+ is kinetically trapped in tetrahedral sites and in a fully oxidized structure, consistent with the reduction of coordination number observed in EXAFS. Although in a reduced state, computation shows that Mn3+ states are stabilized relative to those of oxygen and that the highest occupied molecular orbital (HOMO) is thus dominated by oxygen states. Furthermore, the Mn3+(Td) induces local strain on the oxide sublattice as observed in Raman spectra and results in a reduced gap between the HOMO and the lowest unoccupied molecular orbital (LUMO). The confluence of a reduced HOMO-LUMO gap and oxygen-based HOMO results in the facilitation of OER on the application of anodic potentials to the δ-MnO2 polymorph incorporating Mn3+ ions.

Electrochemical trapping of metastable Mn <sup>3+</sup> ions for activation of MnO <sub>2</sub> oxygen evolution catalysts

Electrochemical trapping of metastable Mn 3+ ions for activation of MnO 2 oxygen evolution catalysts

Electrochemical trapping of metastable Mn ³⁺ ions for activation of MnO ₂ oxygen evolution catalysts