Freestanding Three-Dimensional Graphene Macroporous Supercapacitor

Down, Michael and Banks, Craig (2018) Freestanding Three-Dimensional Graphene Macroporous Supercapacitor. ACS Applied Energy Materials, 1 (2). pp. 891-899. ISSN 2574-0962

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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.