Microstructural Effects on Charge-Storage Properties in MnO2-Based Electrochemical Supercapacitors
Microstructural Effects on Charge-Storage Properties in MnO2-Based Electrochemical Supercapacitors
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DOI：
10.1021/am900094e
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发表时间：
2009-05-01
影响因子：
9.5
通讯作者：
Favier, Frederic
中科院分区：
文献类型：
--
作者：
Ghodbane, Ouassim;Pascal, Jean-Louis;Favier, Frederic
针对制备的二氧化锰（MnO 2）微结构，研究和讨论了二氧化锰（MnO 2）基电化学超级电容器的电荷储存机制。通过以下专用合成路线进行一系列MnO 2同素异形相的制备。所得化合物根据其基于1D通道、2D层或3D互连隧道的晶体结构分为三组。1D组包括软锰矿、斜方锰矿、锰钾矿、Ni掺杂钙锰矿（Ni-钙锰矿）和OMS-5。2D和3D组分别由水钠锰矿和尖晶石组成。采用X射线衍射、扫描电子显微镜、Brunauer-Emmett-Teller技术、循环伏安法（CV）和电化学阻抗谱对所制备的MnO 2粉体进行了表征。通过比表面积、电子电导率和离子电导率的测定，讨论了MnO 2微结构对MnO 2基电极电化学性能的影响。证明了在基于MnO 2的电极中的电荷存储机制主要是法拉第的而不是电容性的。发现比电容值按以下顺序增加：软锰矿（28 F（.）g（-1））<镍钙锰矿<斜方锰矿<锰钾矿< OMS-5 <水钠锰矿<尖晶石（241 F（.）g（-1））。因此，增加空腔尺寸和连通性导致电化学性能的改善。与通常的假设相反，MnO 2基电极的电化学性能不依赖于比表面积。电子电导率也显示出有限的影响。然而，MnO 2形式的比电容与相应的离子电导率强烈相关，这显然依赖于微观结构。CV实验证实了在500次充电/放电循环期间所有MnO 2相的良好稳定性。
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 F (.) g(-1)) < Ni-todorokite < ramsdellite < cryptomelane < OMS-5 < birnessite < spinel (241 F (.) 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.