Influence of iron concentration and post-annealing temperature on structure and pseudocapacitive characteristics of a MnO2–Fe2O3 nanocomposite

Abstract

Nanostructured MnO2 and MnO2–Fe2O3 nanocomposites (MF x O; x = 0.1, 0.2, and 0.3) have been synthesized through a low-temperature ball milling process followed by calcination and acid treatment. It was shown that both the post-annealing temperature and iron (Fe) concentration have a significant influence on the crystal structure and electrochemical performance of the MnO2 nanomaterial. The MnO2-RT is exclusively γ-MnO2, while the MF x O is a mixture of α-MnO2 and Fe2O3. In 1 M lithium hydroxide (LiOH) electrolyte, the MF x O shows better performance as electrode material for supercapacitors than the MnO2 nanoparticles, indicating the beneficial effect of composite formation on the electrode performance. The specific capacitance of the MnO2 nanoparticles post-annealed at 200 °C (MnO2-200 °C electrode) reaches an optimal value of 133.8 F g−1 at 0.75 A g−1, while the MF0.1O post-annealed at 200 °C (MF0.1O-200 °C electrode) exhibits the highest value of 180.9 F g−1 at 0.75 A g−1. After 500 cycles, the specific capacitances of the MnO2-200 °C and MF0.1O-200 °C electrodes keep 84.3 and 84.7 % of the initial capacity, respectively. The facile synthesis, high specific capacitance, and good cycle stability of such MF x O electrodes enable their potential applications as electrode material in high-performance supercapacitors.