Room Temperature Synthesis Routes to the 2D Nanoplates and 1D Nanowires/Nanorods of Manganese Oxides with Highly Stable Pseudocapacitance Behaviors

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 MnSO 4 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 well-separated 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 or MnCO 3 precursor can provide a facile soft-chemical route to 2D δ-MnO 2 nanoplates and 1D α-MnO 2 nanowires/nanorods with highly stable pseudocapacitance behaviors.