▎ 摘　　要

Nitrogen doping manipulates the local electronic structure and enhances the binding of the surface with ions present in the electrolyte. This feature improves the device performance in various applications such as fuel cells, biosensors, electronic devices and high-capacity energy storage devices. In this study, we employ Density Functional Theory (DFT) method to study the adsorption behavior of ionic liquids (ILs) on the nitrogen-doped graphene nanofiake surfaces (GNF@1N, GNF@2N, GNF@3N and GNF@4N). We find that the adsorption of ILs on the N-doped GNFs is controlled through several noncovalent interactions (mainly dispersion forces) and the binding process proceeds spontaneously. The Theory of Atoms in Molecules (AIM) and noncovalent interaction (NCI) analyses show that the interactions between ILs and N-doped GNFs are noncovalent in nature. The interaction strength of ILs with the surfaces increases with increasing the number of nitrogen atoms in the nanofiake surfaces and follows the order of GNF@4N...IL > GNF@3N...IL > GNF@2N...IL > GNF@1N...IL. The HOMO-LUMO energy gap of the N-doped GNF surfaces decreases slightly upon IL adsorption. The nitrogen atoms on the nanoflakes significantly affect the binding energy of ILs and the optical properties verified by changes in the calculated UV-Vis absorption spectra. The UV-Vis absorption spectra of the N-doped GNFs are mainly related to the pi((C=C)) -> pi*((C=C)), pi((C=N)) -> pi*((C=N)), and n((N)) -> pi*((C=N)) transitions. These peaks generally become red-shifted upon IL adsorption. The most significant changes in the absorption spectra of the surfaces are seen with adsorption of ILs on the GNF@4N surface due to stronger interaction of ILs with the GNF@4N surface. The transition density matrix (TDM) heal maps based on fragments show that the electron excitation does not cause a significant electron transfer between N-doped GNF surfaces, cations and anions. Therefore, the electron transitions in the N-doped GNF...IL complexes are regarded as local excitation and mainly occur in the N-doped GNF surfaces. Further, this work attempts to lay a fundamental foundation on our understanding of the interfacial interactions at the electrolyte-electrode interface in the solar cells, supercapacitors and ion-batteries. (C) 2020 Elsevier B.V. All rights reserved.