Room temperature synthesis routes to the 2D nanoplates and 1D nanowires/nanorods of manganese oxides with highly stable pseudocapacitance behaviors

Abstract

The 2D nanoplates of δ-MnO 2 and the 1D nanowires/nanorods of α-MnO 2 can be synthesized at room temperature via one-pot oxidation reaction of commercially available divalent manganese compounds. Treating the MnO or MnCO 3 precursor with persulfate ions for 1-2 days yields layered δ-MnO 2 2D nanoplates, whereas the same oxidation reaction for the MnSO4 precursor produces γ-MnO 2-structured 3D urchins. As the reaction time is extended for ∼14-21 days, not only δ-MnO 2 nanoplates but also γ-MnO 2 urchins are changed to wellseparated 1D nanostructured α-MnO 2 materials with controllable diameters. According to N 2 adsorption-desorption isotherm measurements and Mn K-edge X-ray absorption spectroscopy, all the obtained manganate nanostructures show expanded surface areas of ∼50-120 m 2 g -1 and the mixed oxidation state of Mn 3+/Mn 4+, respectively. All the present nanostructured manganese oxides exhibit pseudocapacitance behaviors with large specific capacitance and excellent capacitance retention, highlighting their promising functionality as a supercapacitor electrode. Among the materials under investigation, the δ-MnO 2 2D nanoplates show the largest specific capacitance (∼180-210 F g -1). The present finding clearly demonstrates that the room-temperature oxidation reaction of the MnO orMnCO 3 precursor can provide a facile soft-chemical route to 2D δ-MnO 2 nanoplates and 1D R-MnO 2 nanowires/nanorods with highly stable pseudocapacitance behaviors. © 2011 American Chemical Society.