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

Abstract

The electric double layer (CD) and electrode quantum (CQ) 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 CD and CQ using [EMIM][BF4] ionic liquid as a model electrolyte. Our results indicate that the inclusion of polarization effects can yield higher CD 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 CQ. 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 CD. 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.