Hierarchical porous carbon composite constructed with 1-D CNT and 2-D GNS anchored on 3-D carbon skeleton from spent coffee grounds for supercapacitor

In recent years, biomass-derived carbon electrode materials for energy storage have attracted intensive attention in terms of their natural unique structure, widespread availability and low cost. Herein, a unique hierarchical porous carbon composite material (CGCM@GNS&CNT) was facilely constructed on 3-D carbon skeleton by anchoring 2-D graphene nanosheet (GNS) and 1-D carbon nanotube (CNT) through self-assembling method. The CGs with abundant macroscopic pores were utilized as 3D carbon skeleton, CNT and GNS anchored on them were applied to enhance the specific surface area (SSA) and electrical conductivity. The composite material exhibits large SSA of 460 m 2 g −1 , interconnected conductive network and inherent N, O doping. The CGCM@GNS&CNT electrode achieves a high areal capacitance of 441 mF cm −2 and volumetric capacitance of 90 F cm −3 at 1 mA cm −2 in 1.5 M Na 2 SO 4 electrolyte. More importantly, the CGCM@GNS&CNT-based symmetric supercapacitor affords a remarkable energy density of 31 μWh cm −2 at a power density of 800 μW cm −2 in 1.5 M Na 2 SO 4 . The capacitance retention and coulombic efficiency can retain 102.5% and 100.5% over 2000 cycles, respectively, confirming its superb charge/discharge stability and long-term reversibility. These signify that CGCM@GNS&CNT material holds a considerable promise for electrode application in high-performance supercapacitor.