On the Origin of the Improvement of Electrodeposited MnOx Films in Water Oxidation Catalysis Induced by Heat Treatment.
Manganese oxides (MnOx ) are considered to be promising catalysts for water oxidation. Building on our previous studies showing that the catalytic activity of MnOx 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, Mn3 O4 , Mn2 O3 , MnO2 and birnessite. This analysis identified two major manganese oxides, Mn3 O4 and birnessite, that constitute 97 % of the MnOx films. Moreover, the catalytic improvement on heat treatment at 90 °C is related to the conversion of a small amount of birnessite to the Mn3 O4 phase, accompanied by an irreversible dehydration process. Further dehydration at higher temperature (120 °C), however, leads to a poorer catalytic performance.
Institute of Methods for Material Development, Helmholtz-Zentrum Berlin für Materialien und Energie, Albert-Einstein-Str. 15, 12489 Berlin (Germany).|Department of Physics, Freie Universität Berlin, Arnimallee 14, 14195 Berlin (Germany).
Munirah
M
Khan
Institute of Methods for Material Development, Helmholtz-Zentrum Berlin für Materialien und Energie, Albert-Einstein-Str. 15, 12489 Berlin (Germany). jie.xiao@helmholtz-berlin.de.
Jie
J
Xiao
School of Chemistry and ARC Centre of Excellence for Electromaterials Science, Monash University, Clayton, VIC, 3800 (Australia).
Fengling
F
Zhou
Institute of Methods for Material Development, Helmholtz-Zentrum Berlin für Materialien und Energie, Albert-Einstein-Str. 15, 12489 Berlin (Germany).|Department of Physics, Freie Universität Berlin, Arnimallee 14, 14195 Berlin (Germany).
Mikhail
M
Yablonskikh
School of Chemistry and ARC Centre of Excellence for Electromaterials Science, Monash University, Clayton, VIC, 3800 (Australia).
Douglas R
DR
MacFarlane
School of Chemistry and ARC Centre of Excellence for Electromaterials Science, Monash University, Clayton, VIC, 3800 (Australia). leone.spiccia@monash.edu.
Leone
L
Spiccia
Institute of Methods for Material Development, Helmholtz-Zentrum Berlin für Materialien und Energie, Albert-Einstein-Str. 15, 12489 Berlin (Germany). emad.aziz@helmholtz-berlin.de.|Department of Physics, Freie Universität Berlin, Arnimallee 14, 14195 Berlin (Germany). emad.aziz@helmholtz-berlin.de.
Emad F
EF
Aziz
D002384:Catalysis; D004563:Electrochemistry; D006358:Hot Temperature; D017895:Manganese Compounds / Q000737:chemistry*; D010084:Oxidation-Reduction; D010087:Oxides / Q000737:chemistry*; D014867:Water / Q000737:chemistry*
D017895:Manganese Compounds; D010087:Oxides; D014867:Water; C027424:manganese oxide
electrochemistry; heat treatment; manganese oxides; water oxidation; x-ray absorption