Model of electrical double layer structure at semi-metallic electrode/ionic liquid interface

In this study, we developed a model for the electrical double layer (EDL) structure formed at the semi-metallic electrode/ionic liquid (IL) interface. To reveal the origin of experimentally observed "U-like" nature of capacitance (C)-potential (E) curve at a glassy carbon (semi-metallic) electrode in ILs, the expression of the capacitance of metallic electrode was modified by taking into account the capacitance of the characteristic space charge layer of semiconductor electrode. The concept of density-of-state of semi-metal and the various physicochemical parameters of ions including size and concentration of practically available ILs were considered for the simulation of C–E curve. We succeeded to reproduce the U-like C–E curve at glassy carbon electrode/IL interface in simulation trials with three commercial ILs. The success of simulating the experimental C–E curve for the metallic electrode by the same strategy to exploit the relevant theory and the properties of ILs further validated the present attempt. Our analysis unveils that the capacitances of both compact and diffuse layers significantly contribute to the total capacitance for the EDL formed at semi-metallic electrode/IL interface, while the diffuse layer mainly contributes to the total capacitances of the metallic electrode in ILs. This study also opens a novel route to determine the compressibility factor of IL by simulating experimental C–E curve at metallic electrode.