A Highly Capacitive Graphene/Multiholed N-CNTs Hybrid Evolved from Black Humate-Co-melamine Precursor

Abstract

Black humic acid (BA) is a black mixture of organic macromolecules isolated from humic acid, which has a greater potential for graphene transformation than fulvic acid and ulmic acid because of more and larger aromatic units and higher molecular weights exceeding 5000 Dalton. Here, chemically bonded BA−Co-Melamine precursors are initially constructed using different BA fractions as substrate, Co²⁺ as bridge bond and melamine as ligand. A series of Graphene/N-CNTs hybrids (GNCs) is eventually synthesized after the precursor pyrolysis. Resultantly, Fraction I, separated at a pH value of 4.16, plays a significant role on constructing the BA−Co-Melamine precursor and further producing multiholed GNCs. Due to abundant CNTs, rich mesopores, moderate nitrogen incorporation and a certain graphitized assembly structure, the prepared GNC-I-b has high capacitance performances. The assembled AC//GNC-I-b supercapacitor has high specific capacitance (147 F g⁻¹ at 1 A g⁻¹), rate capability, cycling stability and energy density (16.8 Wh kg⁻¹ at 14.4 kW kg⁻¹). The 2032 coin-type Li//GNC-I-b half-cell has high initial discharge capacity (759 mAh g⁻¹ at 0.03 A g⁻¹), initial Coulombic efficiency (81.8 %), rate performance and cycling stability. Hence, the GNC is a favorable high-performance carbon material hopefully applied as electrode materials of supercapacitors and LIBs.