Graphene nanotube array assists all-wood supercapacitors to access high energy density and stability

Abstract

Porous carbons with advanced nanostructures and volumetric performance are particularly attractive and essential for miniature supercapacitors to access high energy densities and capacitances, both for portable electronics and massive electrical equipments. However, the electrochemical performances and the pore structure are closely bound up, both restricted by pore volume and pore density. Herein, the wood slice (~0.7 mm) with the periodic porous structure is chosen as the basic framework with rich macropores and the graphene nanotube array (GNTA) with mesopores is used as an intermediate structure in situ synthesized to form the substructure in macropores; therefore, the biomass and nanotube array together construct a porous carbon with hierarchical pores and large surface area. On this basis, Cu-Co oxides are coated on the surface of the pores, to increase the capacitance of electrodes for supercapacitor applications. Because of the GNTA, the specific surface area increases from 38.2 to 1086.0 m² g⁻¹, which is quite helpful for the deposition of Cu-Co oxide nanosheets and effectively alleviates their typical self-stacking phenomenon. Meanwhile, the GNTA creates multiscale pores that served as channels for the rapid electron transfer and ion shuttling; as a result, the resistance obviously induces and capacitance increased by 131% (from 323.4 to 747.5 mF cm⁻²). For the assembled all-wood asymmetric supercapacitor, the specific capacitance is 151.2 F g⁻¹ (1 A g⁻¹), the energy density is 53.8 Wh kg⁻¹ with a power density of 900 W kg⁻¹, and the specific capacitance remains extremely stable during the cycling. Our work provides a practical structure–design strategy for high-performance supercapacitors.