On the influence of polarization effects in predicting the interfacial structure and capacitance of graphene-like electrodes in ionic liquids

The electric double layer (C-D) and electrode quantum (C-Q) capacitances of graphene-based supercapacitors are investigated using a combined molecular dynamics and density functional theory approach. In particular, we compare an approach that includes electronic polarization to one that is polarization-free by evaluating both C-D and C-Q using [EMIM][BF4] ionic liquid as a model electrolyte. Our results indicate that the inclusion of polarization effects can yield higher C-D values-in this study by up to 40% around +/- 2 V-which we attribute primarily to the presence of charge smearing at the electrode-electrolyte interface. On the other hand, we find that the polarization-induced distortion of the electronic structure of graphene does not noticeably alter the predicted C-Q. Our analysis suggests that an accurate description of the spatial charge distribution at the graphene interface due to polarization is necessary to improve our predictive capabilities, though more notably for C-D. However, the conventional polarization-free approximation can serve as an efficient tool to study trends associated with both the CQ and CD at the interface of various graphene-like materials. (C) 2015 AIP Publishing LLC.