Narrow Results

Nanocrystal MnO₂ was successful synthesized by hydrothermal method under pulsed magnetic field. The effect of pulsed magnetic field on the nucleation and growth of MnO₂ was studied by XRD and SEM analysis. It was found that the morphology of MnO₂ has been changed comparing without magnetic field. However, there were no different phases presented when pulsed magnetic field was applied.

In this paper, single crystalline 1D tetragonal MnO₂ pen-type nanorods were synthesized by varying the dwell time through a facile hydrothermal route at a reaction temperature of 250°C. X-ray diffraction (XRD) and transmission electron microscopy (TEM) studies showed that the diameter of MnO₂ nanorods decreases from 460 nm to 250 nm with the increase in hydrothermal reaction time from 5 h to 15 h. Field-emission scanning electron microscopy (FESEM) and TEM studies revealed the evolution of improved surface morphology of MnO₂ nanorods that are prepared with longer hydrothermal reaction time. The magnetic properties of the products were evaluated using vibrating sample magnetometer (VSM) at room temperature, which showed that the as-prepared samples exhibit weak ferromagnetic behavior. The effect of diameter on the magnetization values was observed and discussed in detail.

Nanostructured MnO₂ thin films were prepared on two types of substrates, Pt/Ti/SiO₂/Si (PT) and MnO_x/Pt/Ti/SiO₂/Si (MnO_x/PT), by the technique of cyclic-voltammetric electrodeposition. The MnO_x buffer layer was deposited on the PT substrate by pulsed laser deposition (PLD). The as-deposited MnO₂ thin films were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and X-ray photoelectron spectroscopy (XPS). The electrochemical properties of the thin film MnO₂ electrodes were investigated using cyclic voltammetry (CV) in 1 M Na₂SO₄ electrolyte. It was found that the adhesion between the MnO₂ film and the Pt substrate was poor, resulting in cracks and peeling of the MnO₂ film after deposition. However, the adhesion of the MnO₂ film with the MnO_x buffer layer was greatly improved, resulting in superior pseudocapacitive performance of the thin film electrodes. A specific capacitance of about 364 F/g of MnO₂ thin films deposited on the MnO_x buffer layer can be obtained at a scan rate of 10 mV/s in the voltage window between 0 and 0.9 V versus the Ag/AgCl reference electrode. The MnO₂ thin film deposited on the MnO_x/PT substrate exhibits good rate capability and excellent cycle performance, which makes it promising for supercapacitor application.

In this work, hierarchical polythiophene-coated MnO₂ nanosheets have been synthesized employing a modified interfacial process. The materials have been thoroughly characterized by X-ray powder diffraction, Fourier transform infrared spectroscopy and electron microscopy. It is found that the in situ generated polythiophene-coating cannot only retard the overgrowth of nuclei but also stabilize the ultrathin nanosheets (less than 5 nm), and enhance the electronic conductivity of MnO₂ as well. The cyclic voltammetric measurement verifies that the prepared nanocomposite electrode possesses good electro-catalytic activity to oxygen reduction reaction (ORR) in alkaline media. The corresponding electro-catalytic mechanism on ORR is also investigated. The excellent activity of the synthesized nanocomposite brings about an overall 4-electron reduction of oxygen.