▎ 摘　　要

Due to poor pseudocapacitive properties and low packing density, pristine graphene-based supercapacitors have always exhibited inferior gravimetric and volumetric electrochemical performance. Herein, tromethamine functionalized nanocellulose/reduced graphene oxide composites hydrogels (TNGHs) with dense porous structure and high packing density are produced using a one-pot hydrothermal technique. During the reaction, a highconcentration of graphene oxide (GO) solution is used to increase the compactness of the sample. At the same time, tromethamine is used as reducing agent, nitrogen dopant and structure regulator. Furthermore, nanocellulose (NC) can not only be employed as spacers to constrain the extreme agglomeration of graphene, but also be used as reservoirs to boost the diffusion efficiency of electrolytes in the sample. Benefitting from the dense porous structure, pseudocapacitive behavior of the highly-enriched heteroatom functional groups and high packing density, the binder-free symmetric supercapacitors based on TNGH-40 displays ultrahigh gravimetric specific capacitance (342.5 F g(-1)) and volumetric specific capacitance (339.1 F cm(-3)) at 0.3 A g(-1). This innovative strategy makes TNGHs a potential candidate for miniaturized and compact energy storage devices.