On the Importance of Regulating Hydroxyl Coverage on the Basal Plane of Graphene Oxide for Supercapacitors

Reduced graphene oxide (rGO) has been explored as an alternative to graphene as an electrode material for use in supercapacitors, which thus enables highly scalable solution-based processing. To understand the performance of rGO electrodes in supercapacitors, we theoretically investigate model systems by considering OH-functionalized graphene immersed in 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMIM/FSI) ionic liquid. Our specific interest is to understand the influence of varying the hydroxyl content (or O/C ratio) on both the quantum (C-Q) and electric double-layer (C-D) capacitances. Ultimately, the total interfacial capacitance is found to be sensitive to O/C, but is optimized when the suppression of C-D is most effectively mitigated by the enhancement in C-Q. Our findings clearly demonstrate that the use of GO materials has the potential to enhance supercapacitor performance significantly but will require careful control of both the concentration and composition of oxygen functional groups along the basal surface.