National Laboratory of Solid State Microstructures, College of Engineering and Applied Sciences and Institute of Materials Engineering, Nanjing University , Nanjing, Jiangsu 210093, People's Republic of China.
ACS Appl Mater Interfaces. 2014 Oct 22;6(20):17637-46. doi: 10.1021/am505622c. Epub 2014 Oct 6.
Hierarchically porous yet densely packed MnO2 microspheres doped with Fe3O4 nanoparticles are synthesized via a one-step and low-cost ultrasound assisted method. The scalable synthesis is based on Fe(2+) and ultrasound assisted nucleation and growth at a constant temperature in a range of 25-70 °C. Single-crystalline Fe3O4 particles of 3-5 nm in diameter are homogeneously distributed throughout the spheres and none are on the surface. A systematic optimization of reaction parameters results in isolated, porous, and uniform Fe3O4-MnO2 composite spheres. The spheres' average diameter is dependent on the temperature, and thus is controllable in a range of 0.7-1.28 μm. The involved growth mechanism is discussed. The specific capacitance is optimized at an Fe/Mn atomic ratio of r = 0.075 to be 448 F/g at a scan rate of 5 mV/s, which is nearly 1.5 times that of the extremely high reported value for MnO2 nanostructures (309 F/g). Especially, such a structure allows significantly improved stability at high charging rates. The composite has a capacitance of 367.4 F/g at a high scan rate of 100 mV/s, which is 82% of that at 5 mV/s. Also, it has an excellent cycling performance with a capacitance retention of 76% after 5000 charge/discharge cycles at 5 A/g.
通过一步法和低成本的超声辅助方法合成了具有 Fe3O4 纳米粒子掺杂的分级多孔且密集堆积的 MnO2 微球。这种可扩展的合成方法基于 Fe(2+)，并在 25-70°C 的恒定温度范围内通过超声辅助成核和生长。直径为 3-5nm 的单晶 Fe3O4 颗粒均匀分布在整个球体中，没有颗粒在表面。通过对反应参数的系统优化，得到了孤立、多孔且均匀的 Fe3O4-MnO2 复合球体。球体的平均直径取决于温度，因此可以在 0.7-1.28μm 的范围内进行控制。讨论了所涉及的生长机制。在扫描速率为 5mV/s 时，Fe/Mn 原子比 r = 0.075 时的比电容优化值为 448F/g，是 MnO2 纳米结构极高报道值（309F/g）的近 1.5 倍。特别是，这种结构允许在高充电率下显著提高稳定性。在 100mV/s 的高扫描速率下，该复合材料的电容为 367.4F/g，是在 5mV/s 时的 82%。此外，它具有出色的循环性能，在 5A/g 的电流密度下进行 5000 次充放电循环后，电容保持率为 76%。
