Preparation of MnO2/carbon nanowires composites for supercapacitors

MnO₂/carbon nanowires composites (CNWMn) have been prepared through a simple hydrothermal method using carbon nanowires (CNW) as the both reducing agents and scaffolds for MnO₂ growth. The crystalline phase of CNWMn is closely related to the hydrothermal reaction time, which has a profound impact on the electrochemical performance of CNWMn composites. Typically, the CNMWn2 (reaction time is 2 h) exhibits a highest specific capacitance of 465 F g⁻¹ at the current density of 1 A g⁻¹ in three-electrode systems. In addition, a two-electrode asymmetric system has also been fabricated using CNWMn2 and porous carbon nanowires (PCNW) as positive and negative electrode, respectively. The asymmetric system presents a maximum energy density of 39.2 Wh kg⁻¹ at the current density of 0.5 A g⁻¹, which is much higher than that of traditional sense supercapacitors. Moreover, the asymmetric system exhibits excellent rate capability (high energy density of 24.2 Wh kg⁻¹ at the current density of 10 A g⁻¹) and high cycle stability with only 7% loss of its initial capacitance after 2000 cycles.