Shape-Controlled Synthesis of One-Dimensional MnO2 via a Facile Quick-Precipitation Procedure and its Electrochemical Properties

MnO2 with different crystallographic forms (α, γ) and morphologies (needles, rods, and spindles) was fabricated via a facile quick-precipitation procedure at a low temperature (about 83 °C) without using any templates or surfactants. The proposed mechanism is focused on the different reaction parameters that affect the behaviors of MnO6 octahedron units (basic structural framework of MnO2), which then exert an influence on the formation and stack of nuclei in the crystal growth process. Specific capacitances (C s) calculated according to the area of the cyclic voltammograms (CV) curves were 233.5, 83.1 F·g−1 for the needle- and 95.5, 29.3 F·g−1 for the spindle-like products at the scan rate of 5, 100 mV·s−1, respectively. The C s of needle-like samples calculated by discharge curves at the current density of 2 mA·cm2 is 209.8 F·g−1, close to the value calculated by CV curves at the scan rate of 5 mV·s−1. This methodology facilitates us to synthesize MnO2 with discrepant one-dimensional (1D) nanostructures via a quick, simple, and mild route and may be readily extended to the preparation of many other oxide nanoparticles.