Freestanding Three-Dimensional Graphene Macroporous Supercapacitor

Abstract

The capacitive performance of three-dimensional (3D) freestanding graphene macroporous material (3D-G) fabricated via a chemical vapor deposition (CVD) methodology is comprehensively investigated for application as a potential supercapacitor material, without any mechanical support, for the first time. The 3D-G exhibits a capacitance of 266 μF when charged at 16.6 μA g-1 in an aqueous electrolyte, a significant improvement over a freestanding 3D reticulated vitreous carbon (3D-RVC) macroporous alternative in the same electrolyte and conditions which exhibits a value of only 20 μF. Further improvements in energy storage are demonstrated by utilizing ionic liquids as the electrolytic component. [C4MIM][BF4] facilitates capacitative values from 287 up to 636 μF for the current range 6.66 mA g-1 down to 16.6 μA g-1. The 3D graphene supercapacitors also display a specific energy density of 40.94 W h kg-1 and a power density of 29.33 kW kg-1. Utilizing the ionic liquids [C4MIM][NTf2], [C4MIM][PF6], and [C4MIM][BF4], we demonstrate that the capacitance of the 3D-G is influenced by ion mobility and the molecular mass of the electrolyte which has a profound effect upon the formation of the EDLC upon the graphene's electrode surface; higher molecular weights develop the charge double layer more slowly, resulting in a slightly poorer capacitive performance.