Facile synthesis of graphene nanosheets from humic acid for supercapacitors

A simple, cost-effective, and environmentally friendly route was developed to synthesize graphene nanosheets from humic acid via preliminary carbonization coupled with oxidation-exfoliation-thermal reduction. Such graphene nanosheets have a high specific surface area (495m2·g−1) with large pore volume (2.987cm3·g−1), unique interconnected mesoporous structure and uniform oxygen-containing functional groups in layered graphene framework, which offer a favorable and efficient pathway for the electrolyte propagation and transportation. The electrodes of supercapacitors made from these graphene nanosheets exhibit a maximum specific capacitance of 272F·g−1 at the current density of 50mA·g−1 in aqueous electrolyte, and possess excellent rate capability, low resistance, superior cycling performance with over 96.5% initial capacitance retention after 8000cycles. The corresponding supercapacitors deliver a desirable energy density of 6.47Wh·kg−1 at a powder density of 2250W·kg−1. This study demonstrates a promising synthesis route for large-scale production of graphene nanosheets from renewable and green humic acid for high performance supercapacitors. •Renewable and green humic acid used as resource to synthesize graphene nanosheets.•Graphene nanosheets exhibit high specific surface with large pore volume.•Such synthetic graphene nanosheets contain interconnected mesoporous structure.•Graphene nanosheets have uniform oxygen-containing functional groups in framework.•Supercapacitors with graphene as electrodes show superior capacitive behaviors.