Facile Low-temperature Chemical Synthesis and Characterization of a Manganese Oxide/multi-walled Carbon Nanotube Composite for Supercapacitor Applications

Abstract

<TEX>$Mn_3O_4$</TEX>/multi-walled carbon nanotube (MWCNT) composites are prepared by chemically synthesizing <TEX>$Mn_3O_4$</TEX> nanoparticles on a MWCNT film at room temperature. Structural and morphological characterization has been carried out using X-ray diffraction (XRD) and scanning and transmission electron microscopies (SEM and TEM). These reveal that polycrystalline <TEX>$Mn_3O_4$</TEX> nanoparticles, with sizes of about 10-20 nm, aggregate to form larger nanoparticles (50-200 nm), and the <TEX>$Mn_3O_4$</TEX> nanoparticles are attached inhomogeneously on MWCNTs. The electrochemical behavior of the composites is analyzed by cyclic voltammetry experiment. The <TEX>$Mn_3O_4$</TEX>/MWCNT composite exhibits a specific capacitance of <TEX>$257Fg^{-1}$</TEX> at a scan rate of <TEX>$5mVs^{-1}$</TEX>, which is about 3.5 times higher than that of the pure <TEX>$Mn_3O_4$</TEX>. Cycle-life tests show that the specific capacitance of the <TEX>$Mn_3O_4$</TEX>/MWCNT composite is stable up to 1000 cycles with about 85% capacitance retention, which is better than the pure <TEX>$Mn_3O_4$</TEX> electrode. The improved supercapacitive performance of the <TEX>$Mn_3O_4$</TEX>/MWCNT composite electrode can be attributed to the synergistic effects of the <TEX>$Mn_3O_4$</TEX> nanoparticles and the MWCNTs, which arises not only from the combination of pseudocapacitance from <TEX>$Mn_3O_4$</TEX> nanoparticles and electric double layer capacitance from the MWCNTs but also from the increased surface area, pore volume and conducting property of the MWCNT network.