Adsorption mechanism of amino acid ionic liquids on the N-doped graphene surface for electrochemical double layer capacitors: A density functional theory study

Background: The interfacial interaction between amino acid ionic liquids (AAILs) and graphene (Graphene and N-Graphene) is crucial for understanding the behavior of electrolytes in supercapacitors and ion-batteries. Studying the adsorption mechanism of AAILs on graphene surfaces is the subject of this work. Methods: In this study, we employed the density functional theory to reveal adsorption process. The binding energies, thermochemistry, quantum molecular descriptors, charge transfer, quantum theory of atoms in mol-ecules, noncovalent interaction and energy decomposition analysis were investigated. Significant findings: The adsorption process spontaneously proceeded, and the highest occupied molecular orbi-tal-lowest unoccupied molecular orbital energy gap was reduced slightly upon AAILs adsorption. Nitrogen doping significantly guides the local distribution of electrons and improves the combination of ions, and charge transfer between AAILs and N-Graphene was greater than between AAILs and Graphene. Thus, N-Graphene might exhibit better performance than Graphene. Furthermore, the adsorption was noncovalent in nature, which is crucial to the diffusion of ions in electrolyte-electrode systems. The above results could offer a new angle of view on graphene-AAIL and help in designing novel systems for electrochemistry applications.