Nanocellulose/Reduced Graphene Oxide Composite Hydrogels for High-Volumetric Performance Symmetric Supercapacitors

Abstract

When graphene is used as an electrode material for supercapacitors, it tends to have minor volumetric specific capacitance (<200 F cm–3) and low volumetric energy density (<10 Wh L–1) due to its small packing density and poor pseudocapacitive properties. Herein, nanocellulose/reduced graphene oxide composite hydrogels (NCGHs) with a dense porous structure and large packing density are prepared via a simple hydrothermal method using graphene oxide (GO) and nanocellulose (NC) as a reacting substance. In the reaction system, the high-concentration GO solution provides the driving force for the formation of the dense porous structure of NCGHs through the strong π–π stacking interaction between graphene sheets. NC is used as a physical spacer, and its main function is to inhibit the excessive aggregation of NCGHs. Moreover, the super hydrophilicity of NC can also allow it to be used as an electrolyte reservoir to promote the infiltration of NCGHs by the electrolyte. Meanwhile, the oxygen-containing functional groups retained in NCGHs after the hydrothermal reaction can also enhance their wettability and pseudocapacitance. Consequently, the NCGH-40 based binder-less symmetric supercapacitors delivers a high volumetric capacitance (351.8 F cm–3), a large volumetric energy density (12.2 Wh L–1), and a good rate capability of 80.4% even at 10A g–1. Above all, a capacitance augment of 10.4% is achieved after 10,000 cycles at 10 A g–1, confirming its brilliant cycling stability. These parameters suggest that NCGHs can be applied in next-generation energy storage devices with high volumetric energy density.