First Principles Calculations of 1-methoxymethyl-1-methylpyrrolidinium and 1-ethyl-3-methylimidazolium Adsorption on Graphene

We focused on the basic adsorption properties of two types of cations, viz., 1-methoxymethyl-1-methylpyrrolidinium (MMMP) and 1-ethyl-3-methylimldazolium (EMI), on graphene, as a first step in investigating the properties of carbon electrodes in an electric double layer capacitor. To clarify the basic adsorption properties, we used first principles calculation based on the density functional theory with the generalized gradient approximation for the exchange-correlation energy. We investigated the electrical dipole moment formed between the cations and graphene and found that electric dipole moment per cation formed by MMMP is larger than by EMI. In addition, we found that intramolecular bindings of MMMP are stronger than those of EMI. Based on these results, we conclude that MMMP is more suitable as the material for electric double layer capacitor than EMI.