Structural Distortion in MnO2 Nanosheets and Its Suppression by Cobalt Substitution

Abstract

Co–Mn oxide nanosheets with the chemical composition H0.23Co0.23Mn0.77O2 (C23M77NS) and MnO2 nanosheets (M100NS) were prepared by exfoliation of layer-structured oxides via chemical processing in an aqueous medium. The optical properties of C23M77NS and M100NS were compared using UV-Vis spectroscopy, and the valence states of Mn and Co and local structures around them were examined using X-ray absorption spectroscopy. M100NS with an average Mn valence of 3.6 exhibits large structural distortion, whereas C23M77NS with an average Mn valence of 4.0 does not exhibit structural distortion. Spontaneous oxidization of Mn occurs during ion-exchange and/or exfoliation into nanosheets. These results have originated the hypothesis that structural distortion determines the valence state of Mn in compounds with CdI2-type-structured MnO2 layers.

Direct Proof of the Reversible Dissolution/Deposition of Mn2+/Mn4+ for Mild‐Acid Zn‐MnO2 Batteries with Porous Carbon Interlayers

“…It is remarkable that the Mn L edge sXAS spectra shift to the lower energies at the SOC of 50% and then back to the higher energies at the SOC of 100%, indicating that the average oxidation state of Mn ions decreased and then increased again during charge. [42][43][44] Figure S9 in the Supporting Information shows the ex situ Mn Kedge XANES spectra of MnO 2 electrodes retrieved at various discharge/charge states. The oxidation states of Mn were calibrated using the linear correlation between oxidation states and XANES edge positions of the reference standards of Mn II O, Mn III OOH, and Mn IV O 2 .…”

Elucidating the Active Sites and Synergies in Water Splitting on Manganese Oxide Nanosheets on Graphite Support

“…line scans below and Figure S5, Supporting Information), which agrees with other observations of MnO 2 NS. [ 44,45 ] The modeled height obtained from the DFT calculations is between 0.45 nm and 0.55 nm (Figure 1c and Figure S15, Supporting Information), which is close to the crystallographic thickness of 0.5 nm. [ 31 ] Since the measurements in Figure 1b were carried out in air, while our calculations were performed in a vacuum and at zero temperature and water and cations as spacers between the layers [ 41 ] were neglected for simplicity, both results are in reasonable agreement.…”

Facile synthesis of single-crystalline MnO2nanowire arrays with high photothermal catalytic activity

“…However, the participation of the b-MnO 2 photocatalysis in the reaction can be ruled out because its band gap is B2.6 eV (absorption edge E 480 nm). 30 Also, photoluminescence measurements confirmed that b-MnO 2 hardly exhibits emission even under the band gap excitation at À196 1C, while the vibrational excitation of OPD can be neglected due to the weak absorption of organic molecules. Thus, the light absorbed by b-MnO 2 is efficiently converted into heat via non-radiative relaxation under the present conditions.…”