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 °C and 75 °C. The specific capacitance at 1 A g^-1 increases from 365 F g^-1 at 0 °C to 546 F g^-1 at 75 °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 °C and 82.4% at 75 °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.