Abstract
Mn oxides, which are relatively low cost with low toxicity and environmental friendly, are regarded as one of the most promising candidate materials for pseudo-capacitors. The oxidation state of Mn ion in the oxides (e.g.: +2, +3, +4, +6 and +7) is a very critical factor affecting the specific capacitance. Three Mn oxide films (crystalline Mn2O3, amorphous Mn2Ox, x ∼ 3.74 and crystalline Mn3O4) with different oxidation states of Mn were prepared using a pulsed laser deposition (PLD) method, which show different capacitance performances (crystalline Mn2O3 film > amorphous MnOx film > crystalline Mn3O4 film). X-ray absorption near edge structures (XANES) is applied to investigate the electronic structures of these films. Mn K-edge and L3,2-dege XANES results confirm that the bulk of the amorphous MnOx film is composed of MnO2 and Mn2O3 with Mn4+/Mn3+ ratio of about 3:1. Total electron yield (TEY) XANES at the Mn L3,2-edge which is surface-sensitive, suggests that the amorphous film also contains some Mn3O4 on the surface, which is proposed to be the reason why the amorphous MnOx film shows moderate pseudo-capacitance behavior in between the pure Mn2O3 and Mn3O4 films.
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