Effect of temperature on the pseudo-capacitive behavior of freestanding MnO2@carbon nanofibers composites electrodes in mild electrolyte

Electrospun carbon nanotubes-embedded carbon nanofibers (CNF) fabric is employed as freestanding substrates for in-situ coating MnO2 nanostructures. Birnessite-type MnO2 nanoflakes are observed to grow vertically on individual CNF, thus building hierarchical coaxial architecture. This work presents an extensive study of the effect of temperature on the pseudo-capacitive behavior of the as-prepared freestanding MnO2@CNF composites electrodes in mild Na2SO4 electrolyte. The results show that the MnO2@CNF composites exhibit excellent pseudo-capacitive behaviors at different temperatures between 0 degrees C and 75 degrees C. The specific capacitance at 1 A g(-1) increases from 365 F g(-1) at 0 degrees C to 546 F g(-1) at 75 degrees C, whereas the coulombic efficiency decreases with the increasing temperature, especially at lower charging rate. The cycling stability of the composites strongly depends on the temperature, i.e., 95.3% at 25 degrees C and 82.4% at 75 degrees C. This study provides a fundamental understanding of the temperature-dependent capacitive properties of MnO2 in mild electrolyte, which gives an insight into the supercapacitor design for industrial applications. (C) 2012 Elsevier B.V. All rights reserved.