Institut Charles Gerhardt Montpellier, UMR 5253 CNRS, Equipe AIME, Universite Montpellier II, Place Eugene Bataillon, cc1502, 34095 Montpellier Cedex 5, France.
ACS Appl Mater Interfaces. 2009 May;1(5):1130-9. doi: 10.1021/am900094e.
The charge-storage mechanism in manganese dioxide (MnO2)-based electrochemical supercapacitors was investigated and discussed toward prepared MnO2 microstructures. The preparation of a series of MnO2 allotropic phases was performed by following dedicated synthetic routes. The resulting compounds are classified into three groups depending on their crystal structures based on 1D channels, 2D layers, or 3D interconnected tunnels. The 1D group includes pyrolusite, ramsdellite, cryptomelane, Ni-doped todorokite (Ni-todorokite), and OMS-5. The 2D and 3D groups are composed of birnessite and spinel, respectively. The prepared MnO2 powders were characterized using X-ray diffraction, scanning electron microscopy, the Brunauer-Emmett-Teller technique, cyclic voltammetry (CV), and electrochemical impedance spectroscopy. The influence of the MnO2 microstructure on the electrochemical performance of MnO2-based electrodes is commented on through the specific surface area and the electronic and ionic conductivities. It was demonstrated that the charge-storage mechanism in MnO2-based electrodes is mainly faradic rather than capacitive. The specific capacitance values are found to increase in the following order: pyrolusite (28 Fx g(-1)) < Ni-todorokite < ramsdellite < cryptomelane < OMS-5 < birnessite < spinel (241 Fx g(-1)). Thus, increasing the cavity size and connectivity results in the improvement of the electrochemical performance. In contrast with the usual assumption, the electrochemical performance of MnO2-based electrodes was not dependent on the specific surface area. The electronic conductivity was shown to have a limited impact as well. However, specific capacitances of MnO2 forms were strongly correlated with the corresponding ionic conductivities, which obviously rely on the microstructure. The CV experiments confirmed the good stability of all MnO2 phases during 500 charge/discharge cycles.
针对制备的二氧化锰 (MnO2) 微结构，研究并讨论了基于二氧化锰的电化学超级电容器的电荷存储机制。通过专门的合成途径制备了一系列二氧化锰同素异形体。根据其晶体结构，将得到的化合物分为三组，分别基于一维通道、二维层或三维互连隧道。一维组包括软锰矿、菱锰矿、钡钾锰矿、镍掺杂的钠锰矿 (Ni-钠锰矿) 和 OMS-5。二维和三维组分别由水钠锰矿和尖晶石组成。使用 X 射线衍射、扫描电子显微镜、Brunauer-Emmett-Teller 技术、循环伏安法 (CV) 和电化学阻抗谱对制备的 MnO2 粉末进行了表征。通过比表面积和电子及离子电导率来评论 MnO2 微观结构对基于 MnO2 电极的电化学性能的影响。结果表明，基于 MnO2 的电极的电荷存储机制主要是法拉第的，而不是电容的。比电容值的增加顺序为：软锰矿 (28 Fx g(-1)) < Ni-钠锰矿 < 菱锰矿 < 钡钾锰矿 < OMS-5 < 水钠锰矿 < 尖晶石 (241 Fx g(-1))。因此，增加空腔尺寸和连通性会改善电化学性能。与通常的假设相反，基于 MnO2 的电极的电化学性能不取决于比表面积。电子电导率的影响也有限。然而，MnO2 形态的比电容与相应的离子电导率密切相关，而离子电导率显然取决于微观结构。CV 实验证实了所有 MnO2 相在 500 次充放电循环过程中的良好稳定性。
