Zwitterion Functionalization of Graphene with pH Independent Dispersion Stability: Efficient Electron Mediator for Oxygen Evolution Reaction in Acidic Medium

Abstract

Functionalization of graphene by surfactant has been demonstrated as effective routes for modulating the surface property, enhancing the dispersibility, and expanding the versatile use of graphene in various fields of application. Surfactant configuration is important for functionalization of graphene becauses backbone of surfactant mainly interacts with the graphene via π—π interaction, which has a strong effect on the graphene functionalization efficiency, and the side functional group interacts with the dispersion medium, which affects the dispersibility of graphene. However, detailed study on the effect of surfactant configuration is still quite insufficient. In this work, we examine the effect of surfactant to graphene on the molecular level through experimental and computational studies. We demonstrated that the number of carbon atoms and electron deficiency in the surfactant backbone is closely related to its adsorptivity on graphene surface, and perylene diimide (PDI) can function as an efficient backbone for the graphene functionalization. Moreover, zwitterionic amino N-oxide (–NO) side functional group is found to improve the dispersion stability of graphene in aqueous medium with various pH levels via the hydration repulsion effect. Consequently, PDI–NO functioned as an efficient surfactant for the functionalization of graphene with pH independent dispersibility in aqueous solution. As-prepared PDI–NO functionalized graphene was successfully demonstrated in oxygen evolution reaction as an electron mediator for enhancing the performance of homogeneous electrocatalyst. We believe that our results could bring significant advances in achieving highly dispersive graphene flakes via functionalization, and help to expand the scope of graphene applications.