Electronic structure related electric-double-layer effects on heterogeneous ET kinetics on graphene electrode

Abstract

The effects of electric-double-layer (EDL) structures on the heterogeneous electron transfer (ET) kinetics on graphene and metal electrodes are compared through theoretical modeling and finite-element-method (FEM) simulation, by combining the Marcus–Hush–Chidsey ET theory and a dynamic diffuse double layer model. It is shown that, due to the much lower density of states (DOS) near the Fermi energy level, the graphene electrodes would exhibit significantly different EDL structures (e.g., charge density and electrostatic potential distributions) from that on usual metal electrodes at the same electrode potential. In the cases when the EDL structures can impact the heterogeneous ET kinetics at electrochemical interfaces, for examples, when solution contains inadequate supporting electrolyte or the electrodes have nanometer sizes, the voltammetric responses of graphene electrode can be significantly different from that of the usual metal electrodes. In general, the low DOS of graphene makes the electrostatic potentials in the diffuse EDL less pronounced due to the considerable quantum capacitance; therefore, the diffuse EDL effect on the heterogeneous ET kinetics is attenuated. This makes the graphene-based electrodes suitable for application in weakly supported solution.