Insights into binding mechanisms of size-selected graphene binders for flexible and conductive porous carbon electrodes

Abstract

Two-dimensional (2D) materials, such as reduced graphene oxide (rGO), MXene, and transition metal dichalcogenides (TMDs) have been recently used as a conductive binder for manufacturing carbon electrodes in energy storage applications. It has been demonstrated that 2D nanosheets can be used to replace the insulating polymer binders, as well as providing flexible electrodes. However, the optimum dimension of 2D nanosheets has not yet been explored for maximizing the electrode performance. Herein, we have investigated the binding mechanisms of size-selected graphene (GP) nanosheets, in which the activated carbon (AC) is used as an active porous material. The unique morphology of the electrode surface, resulting from different graphene dimensions, plays a crucial role in the charge storage mechanism in terms of the ability of ion diffusion at the outer and inner surface. The use of the medium-sized graphene nanosheet (mGP; ∼350 nm) as a binder in the AC electrode displays superior improvement of charge storage by 20% as well as good charge retention by 10% compared to the binder-free AC electrode. This is due to a presence of the continuous conductive mGP network, leading to the formation of hierarchical interconnected porous ACs with excellent conductivity that allows the access of electrolyte ions and facilitates the transport of charged ions through the electrochemically active surface area (ECSA) of the electrode. These results demonstrate that the optimized graphene nanosheet binder with the unique morphology could enhance the capacitive performance of porous carbon materials, which is beneficial for development of scaling-up supercapacitors and various energy storage devices.