Abstract Spherical MnO2 nanoparticles were synthesized at room temperature via template-free sonochemical reduction of potassium permanganate using a reducing agent of polyethylene glycol under two different time durations (i.e., 15 min (M1) and 30 min (M2)). The M2 sample exhibited the α-phase of the tetragonal MnO2 structure, whereas the M1 sample showed the δ-MnO2 phase. For microstructural analyses, the M2 sample revealed a spherical structure of the nanoparticles with an average grain size of 20–30 nm. When using spherical MnO2 nanoparticles (i.e., M2) as an electrode material for the supercapacitor device, the maximum specific capacitance of 136 F/g was observed at the current density of 0.5 A/g. The device displayed an excellent cyclic stability of 72% after 5000 charge/discharge cycles, and showed a high energy density up to 38.3 Wh/kg. These results suggest that the sonochemically-synthesized spherical MnO2 nanoparticles could be used as a suitable electrode material for high-energy electrochemical supercapacitors.

中文翻译：

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用于高能超级电容器电极的球形 α-MnO 2 纳米粒子的无模板快速声化学合成

摘要 在室温下，使用聚乙二醇还原剂，在两种不同的持续时间（即 15 分钟 (M1) 和 30 分钟 (M2)）下​​，通过无模板声化学还原高锰酸钾，合成了球形 MnO2 纳米颗粒。M2 样品显示出四方 MnO2 结构的 α 相，而 M1 样品显示出 δ-MnO2 相。对于微观结构分析，M2 样品显示纳米颗粒的球形结构，平均粒径为 20-30 nm。当使用球形 MnO2 纳米粒子（即 M2）作为超级电容器装置的电极材料时，在 0.5 A/g 的电流密度下观察到的最大比电容为 136 F/g。该器件在 5000 次充放电循环后表现出 72% 的优异循环稳定性，并显示出高达 38.3 Wh/kg 的高能量密度。