MnO2 was self-grown on carbon fiber paper (CFP) via a facile redox reaction, which is constructed by interconnected ultrathin nanosheets array. The CFP acts as both a supporting scaffold and a reducing agent for MnO2 growth. The obtained MnO2/CFP composite was directly used as electrodes for supercapacitors, delivering a high specific capacitance of 713.7 F/g (0.5 A/g). Cyclic stability testing of the MnO2/CFP electrode reveals 86.8% retention in specific capacitance after 1200 cycles at 5.0 A/g. The nanosheet morphology of the MnO2 on CFP brings about more efficient electroactive sites and facilitates the electrolyte penetration, allowing greater access for ions to active reaction sites. Hence, the attractive electrochemical performances exhibited by this MnO2/CFP electrode endow them potentially promising candidates for supercapacitors.

•α-MnO2 nanorods were facilely prepared with chemical precipitation method at 80 °C.•The morphologies turn from tiny dendrites clusters to nanorods with reaction time.•The electromagnetic properties correlate closely with morphologies and reaction time.One-dimensional α-MnO2 nanorods were fabricated by using low-temperature water-bathing chemical precipitation method at 80 °C. The crystalline structures, morphological evolution process and microwave absorption properties were systematically investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and measurement of electromagnetic parameters. The results show that the morphological structures and electromagnetic properties have close relationship with the reaction time. With the prolonging of the treatment time, the as-synthesized products turn from microspheres constituted of tiny dendrites to nanorods with diameters of 20–30 nm and lengths up to 1–2 μm. The electromagnetic characterization shows that the dielectric constants and magnetic permeability values show decreasing trends with the increasing frequency, however, the dielectric and magnetic loss tangents all increase with frequency. The electromagnetic absorption properties of the products have close relationship with the morphologies and thicknesses of the samples. With a thickness of 3 mm, an absorbing peak value of −25 dB was achieved for the sample treated for 24 h. The microwave absorption properties of MnO2 can be attributed mainly to interfacial polarization, space charge polarization and relaxation phenomena.

The α-MnO2 nanorods were successfully prepared by hydrothermal methods at 160 °C for 48 h. X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were employed to characterize the morphology and microstructure of the final product. The results show that the final product is the pure tetragonal α-MnO2 phase with rod-like nanostructure in diameters 30 nm and lengths up to 0.5–1 μm. The dielectric and the electrical properties of the α-MnO2 nanorods were also analyzed and discussed at a range of the temperature from 223 K to 393 K. The dielectric constants and dielectric loss tangents both increase with the rising temperature and decrease with frequency. The electrical resistivity values also decrease with the rising temperature and frequency. It is also found that the dielectric loss of α-MnO2 mainly results from the space polarization and the temperature dependence of resistivity follows the Arrhenius Equation.The α-MnO2 nanorods with diameters of 30 nm and lengths up to 0.5–1 μm were prepared with hydrothermal methods. The nanorods have smooth and flat surfaces.The curves of correlation between the reciprocal of temperature (1000/T) and the logarithm of electric resistivity (log ρ) are found anomalies at about 303 K despite the frequencies tested.Highlights► The α-MnO2 nanorods were prepared with hydrothermal methods. ► The nanorods are with diameters of 30 nm and lengths up to 0.5–1 μm. ► The dielectric properties increase with temperature but decrease with frequency. ► The logarithm curves of electric resistivity are found anomalies at about 303 K.