导电石墨烯孔道内双电层结构的研究

Study onelectric double layers inside the conducting graphene nanopores

为有效开发和利用新能源,人们迫切需要高性能的超级电容器提供能量的存储和转换.在超级电容器中双电层结构扮演着关键性的角色.本文利用分子动力学方法通过建立开放的石墨烯纳米孔道(1~2 nm),研究了KCl溶液在纳米孔道内的双电层结构,同时也比较了恒电量模拟(Q)和恒电势模拟法(U)下双电层结构的异同.结果表明在恒电势模拟法考虑了导电石墨烯壁的镜像作用使结果更符合实验中的材料系统.而石墨烯壁的镜像作用能额外吸附离子从而增强孔道内部的阴阳离子,这可能有助于电极电容的提升.通过对不同孔道高度的研究,本文发现水分子作为介电材料在水基超级电容器中发挥着决定性的作用.它能在很大程度上抵消不同离子和不同孔道高度下双电层的变化,从而在不同情况下获得了相似的电容.

In order to effectively develop and utilize new energy, people urgently need high-performance supercapacitors to provide energy storage and conversion. Electric double layer structure plays a key role in supercapacitors. In this work, the molecular dynamics simulation was taken to an open graphene nanochannel (1~2 nm ), and the double-layers structure of KCl solution inside the nanochannel was studied. Meanwhile, the similarities and differences of the double-layer structure under fixed charge simulation ( Q ) and constant potential simulation ( U ) were compared. The results show that the mirror image effect of the conducting graphene wall is considered in the constant potential simulation method, which makes the results more consistent with the practical materials. The mirror image effect can absorb extra ions. Thus it enhances the concentratiosn of anion and cation in the pore, which may contribute to the improvement of electrode capacitance. Through the study of different channel heights, it is found that water molecules play a decisive role as dielectric materials in water-based supercapacitor. It can largely offset the change of electric double layer under different ions and different channel heights, resulting in a similar capacitance under different conditions.