On the Origin of the Improvement of Electrodeposited MnOx Films in Water Oxidation Catalysis Induced by Heat Treatment. Issue 11 (4th May 2015)

• Record Type: Journal Article
• Authors: Khan, Munirah; Xiao, Jie; Zhou, Fengling; Yablonskikh, Mikhail; MacFarlane, Douglas R.; Spiccia, Leone; Aziz, Emad F.
• Is Part Of: ChemSusChem. Volume 8:Issue 11(2015:Jun.)
• Page Start: 1980
• Page End: 1985
• Publication Date: 2015-05-04
• Subjects: Green chemistry -- Periodicals; Sustainable engineering -- Periodicals; Chemistry -- Periodicals; Chemical engineering -- Periodicals; 660
• DOI: 10.1002/cssc.201500330
• Languages: English
• ISSNs: 1864-5631

Abstract

<abstract abstract-type="main" xml:lang="en"> <title>Abstract</title> <p>Manganese oxides (MnO_{<italic>x</italic>}) are considered to be promising catalysts for water oxidation. Building on our previous studies showing that the catalytic activity of MnO_{<italic>x</italic>} films electrodeposited from aqueous electrolytes is improved by a simple heat treatment, we have explored the origin of the catalytic enhancement at an electronic level by X‐ray absorption spectroscopy (XAS). The Mn L‐edge XA spectra measured at various heating stages were fitted by linear combinations of the spectra of the well‐defined manganese oxides—MnO, Mn₃O₄, Mn₂O₃, MnO₂ and birnessite. This analysis identified two major manganese oxides, Mn₃O₄ and birnessite, that constitute 97 % of the MnO_{<italic>x</italic>} films. Moreover, the catalytic improvement on heat treatment at 90 °C is related to the conversion of a small amount of birnessite to the Mn₃O₄ phase, accompanied by an irreversible dehydration process. Further dehydration at higher temperature (120 °C), however, leads to a poorer catalytic performance.</p> </abstract>