Nanocellulose/N, O co-doped graphene composite hydrogels for high gravimetric and volumetric performance symmetric supercapacitors

Abstract

The poor volumetric electrochemical performance of graphene greatly limits its application in miniaturized electronic equipment. To solve this problem, nanocellulose/N, O co-doped graphene composite hydrogels (NGCHs) were synthesized by a simple hydrothermal method using high-concentration graphene oxide (GO) solution, ammonia and nanocellulose (NC) as reaction precursors. During the reaction process, the strong π-π stacking interaction between graphene sheets in high-concentration GO solution was the main driving force for the formation of the dense structure of NGCHs. Ammonia was used as a reducing agent, nitrogen dopant and modifier of the sample structure. NC was used as a spacer, and the electrostatic repulsion between its oxygen-rich surface and GO sheet can prevent the excessive agglomeration of graphene. In addition, NC can also be used as electrolyte reservoirs to facilitate the infiltration of electrolytes in NGCHs. The resulting NGCHs show dense mesoporous-dominant structure, abundant heteroatom-rich functional groups (16.46–18.25 at%) and high packing density (1.22–1.35 g cm−3). Consequently, the NGCH-150 based binder-free symmetric supercapacitors presents high gravimetric (299.7 F g−1) and volumetric (404.6 F cm−3) capacitance at 0.3 A g−1, an exceptional rate capability of 81.6% up to 10 A g−1 and good cycle ability (93.8% after 10,000 cycles). Therefore, our experimental strategy is hopeful to prepare electrode materials for the next-generation miniaturized energy storage devices.