Li Song, Zhu Mengyang, Feng Guang
State Key Laboratory of Coal Combustion, School of Energy and Power Engineering, Huazhong University of Science and Technology, Wuhan 430074, People's Republic of China. Nano Interface Center for Energy (NICE), School of Energy and Power Engineering, Huazhong University of Science and Technology, Wuhan 430074, People's Republic of China.
J Phys Condens Matter. 2016 Nov 23;28(46):464005. doi: 10.1088/0953-8984/28/46/464005. Epub 2016 Sep 14.
The effects of dication symmetry on the structure and capacitance of the electrical double layers (EDLs) of dicationic ionic liquids (DILs) near graphene electrodes were investigated by molecular dynamics (MD) simulation in this work. Symmetrical 1-hexyl-3-dimethylimidazolium dibis(trifluoromethyl)imide and asymmetrical 1-(1-trimethylammonium-yl-hexyl)-3-methylimidazolium di[bis(trifluoro-methanesulfonyl)-imide] (C6(tma)(mim)2) were both employed. Radial distribution function (RDF) analysis of the two DILs revealed a shorter distance between the cation-anion pairs in symmetrical C6(mim)22), which was attributed to the closely packed imidazolium ring-anion pairs. In contrast, the trimethylammonium head groups and anions exhibit a relatively longer distance, but a stronger correlation in asymmetrical C6(tma)(mim)2. In addition, it was illustrated that more symmetrical DIL ions in EDLs are distributed near graphite electrodes and exhibit closer distances to the electrode, which is most probably due to the parallel orientation of imidazolium rings, reducing the distance between the cation and the graphene. In contrast, asymmetrical DILs, with one trimethylammonium head group and one imidazolium ring in the dications, are loosely packed due to their tilting orientation near graphene surfaces. However, the capacitance-potential (C-V) curves of the two DILs are almost the same, regardless of the opposite sign of potential of zero charge (PZC), indicating the insignificant influence of dication symmetry on the capacitance of DIL-based supercapacitors.
在本工作中，通过分子动力学（MD）模拟研究了双阳离子对称性对石墨烯电极附近双阳离子离子液体（DILs）的双电层（EDLs）结构和电容的影响。使用了对称的1-己基-3-二甲基咪唑鎓双双（三氟甲基）亚胺和不对称的1-（1-三甲基铵基己基）-3-甲基咪唑鎓双双（三氟甲磺酰）亚胺。对这两种DILs的径向分布函数（RDF）分析表明，对称的C6(mim)22中阳离子-阴离子对之间的距离较短，这归因于咪唑鎓环-阴离子对紧密堆积。相比之下，在不对称的C6(tma)(mim)2中，三甲基铵头基和阴离子之间的距离相对较长，但相关性更强。此外，结果表明，双电层中更多对称的DIL离子分布在石墨电极附近，且与电极的距离更近，这很可能是由于咪唑鎓环的平行取向，减小了阳离子与石墨烯之间的距离。相比之下，不对称的DILs，其二阳离子中有一个三甲基铵头基和一个咪唑鎓环，由于它们在石墨烯表面附近的倾斜取向而堆积松散。然而，两种DILs的电容-电位（C-V）曲线几乎相同，无论零电荷电位（PZC）的符号相反，这表明双阳离子对称性对基于DIL的超级电容器的电容影响不大。
