High-density oxygen-enriched graphene hydrogels for symmetric supercapacitors with ultrahigh gravimetric and volumetric performance

The contradiction between the porous structure and density of graphene materials makes it unable to meet the dual requirements of the next generation supercapacitors for gravimetric capacitance and volumetric capacitance. Herein, we successfully synthesized highdensity oxygen-enriched graphene hydrogels (HOGHs) by a one-step hydrothermal method using high concentration graphene oxide (GO) solution and trometamol as precursors. The as-prepared HOGHs samples present a dense 3D network structure and moderate specific surface areas, which leads to a high packing density. In addition, the HOGHs samples also contain abundant oxygen-containing functional groups and some nitrogen-containing functional groups. These heteroatomic functional groups can provide pseudocapacitance for the electrode materials. Therefore, the HOGH-140 based symmetric supercapacitor shows ultrahigh gravimetric and volumetric specific capacitance (325.7 F g(-1), 377.8 F cm(-3)), excellent rate performance and cycling stability. Simultaneously, the symmetric binderfree supercapacitor exhibits high gravimetric specific energy density (11.3 Wh kg(-1)) and volumetric specific energy density (13.1 Wh L-1) in 6 M KOH, respectively. These outstanding properties make the material have a good application prospect in the field of compact energy storage devices. (C) 2021 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.