Impact of typology and density of point defects on capacitance of graphene-based electrodes

Abstract

The influence of defects on graphene quantum capacitance has been widely studied using various modeling approaches and in particular the fixed-band approximation (FBA). However, computational models do not yield results in agreement with experiments and can rarely account for the effect of the metallic substrate. They typically predict capacitance values an order of magnitude higher than experiment. In this paper we assess the capacity of the recently developed interfacial capacitance model (ICM) based on density functional theory (DFT) calculations, to investigate the impact of three point-like defects on graphene capacitance. The modeled defects are single-vacancy, double-vacancy, and Stone-Wales; all defective graphene structures are modeled on Cu(111) substrate. The impact of the density of single-vacancy defects on the capacitance was carefully analyzed. The computations demonstrate that the ICM can predict capacitance of graphene on a metallic substrate in agreement with experiment even in the case of the existence of defect. This suggests that ICM can be generalized for assessing graphene capacitance and interfacial capacitance regardless of morphology of the surface. The results ranged from 1.692 μF cm−2 to 1.872 μF cm−2 for defective models, compared with 1.73 μF cm−2 of pristine model which is in agreement with experiment. Various defective cases were analyzed using density of states, projected density of states, electrons isosurfaces, and structural parameters. The charge separation triggered by defects can be correlated with the increase in capacitance as long as no chemical bonding is triggered by the defect between copper and graphene.