A Computational Study of the Interfacial Structure and Capacitance of Graphene in [BMIM][PF6] Ionic Liquid
A Computational Study of the Interfacial Structure and Capacitance of Graphene in [BMIM][PF6] Ionic Liquid
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DOI：
10.1149/2.019301jes
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发表时间：
2013-01-01
影响因子：
3.9
通讯作者：
Hwang, Gyeong S.
中科院分区：
文献类型：
--
作者：
Paek, Eunsu;Pak, Alexander J.;Hwang, Gyeong S.
石墨烯类电极和离子液体（IL）电解质的组合已经成为电化学双层（EDL）电容器的可行且有吸引力的选择。基于经典分子动力学和密度泛函理论计算，研究了平面石墨烯和[BMIM][PF 6] IL之间的界面电容，特别关注石墨烯/IL界面双电层电容和石墨烯量子电容的相对贡献.研究了不同电荷密度下[BMIM][PF 6]在石墨烯电极附近的微观结构，以提供对EDLs的分子描述，包括BMIM/PF 6堆积和取向、阳离子-阴离子分离和电极电荷屏蔽。虽然IL界面结构表现出一个替代的阳离子/阴离子分层延伸几个纳米，计算的电位分布提供了一个离子厚紧凑的EDL形成的证据。EDL的电容-电势曲线是凸形或钟形的，而石墨烯的量子电容被发现具有凹形或U形的特征，最小值接近于零。因此，我们发现，总的界面电容表现出U形的趋势，与现有的实验观察在一个典型的碳/IL接口。我们的工作突出了量子电容在石墨烯基EDL电容器的整体性能中的重要性。(C)2012年电化学学会。[DOI：10.1149/2.019301jes]版权所有。
A combination of graphene-like electrodes and ionic liquid (IL) electrolytes has emerged as a viable and attractive choice for electrochemical double layer (EDL) capacitors. Based on combined classical molecular dynamics and density functional theory calculations, we present the interfacial capacitance between planar graphene and [BMIM][PF6] IL, with particular attention to the relative contributions of the electric double layer capacitance at the graphene/IL interface and the quantum capacitance of graphene. The microstructure of [BMIM][PF6] near the graphene electrode with varying charge densities are investigated to provide a molecular description of EDLs, including BMIM/PF6 packing and orientation, cation-anion segregation, and electrode charge screening. Although the IL interfacial structures exhibit an alternative cation/anion layering extending a few nanometers, the calculated potential profiles provide evidence of one-ion thick compact EDL formation. The capacitance-potential curve of the EDL is convex-or bell-shaped, whereas the quantum capacitance of graphene is found to have concave-or U-shaped characteristics with a minimum of nearly zero. Consequently, we find that the total interfacial capacitance exhibits a U-shaped trend, consistent with existing experimental observations at a typical carbon/IL interface. Our work highlights the importance of the quantum capacitance in the overall performance of graphene-based EDL capacitors. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.019301jes] All rights reserved.