Interconnected graphene-like nanosheets for supercapacitors

Abstract

The rapid economic development has necessitated increased environmental protection and tremendous efforts have been devoted to designing and preparing environmentally friendly energy storage and conversion devices, including batteries, supercapacitors (SCs), and solar cells. As useful energy storage and conversion devices, SCs have received significant attention due to their high power density, long cycle stability, and rapid charging rate. The performance of SCs largely depends on the electrode materials, which can be composed of metal oxides, conducting polymers, carbon materials, and their composites. Carbon materials, including carbon nanotubes, carbon fibers, porous carbons, template carbons, and graphene-like carbon nanosheets (GCNSs), have attracted significant attention owing to their tailorable pore size and excellent physiochemical stability. GCNSs are considered to be outstanding carbon materials for use in high-performance SC because of their large specific surface area and high electrical conductivity. To date, many carbon precursors have been used to synthesize GCNSs for SCs such as coal, biomass, and chemical by-products. In particular, cheap and abundant chemical by-products for the synthesis of carbon materials can reduce preparation costs and environmental pollution as well as achieve high value-added chemicals. Coal tar, a byproduct of the coal coking process, is rich in aromatic polycyclic hydrocarbon molecules, which can be polymerized, carbonized, and activated to synthesize GCNSs for SCs. In addition, MgO particles can be used as templates due to their stable properties and low-cost compared with other metal oxide templates (e.g. Fe2O3, NiO, or CuO), imparting space confinement and structure guidance during the preparation of GCNSs. Herein, we report a facile method for the preparation of interconnected graphene-like nanosheets (IGNSs) from coal tar by MgO templating combined with in-situ KOH activation. The IGNSs were obtained after the impurity removal by repeated washing with dilute acid. The as-synthesized IGNSs feature high specific surface area of up to 2887 m2 · •g−1 and abundant hierarchical short pores, which provide abundant active sites for ion adsorption, supply plentiful channels for fast ion transport and boost electrical conductivity. As electrodes for SCs, IGNSs manifest high specific capacitance value of up to 313 F·•g−1 at 0.05 A·•g−1, good rate capability of 261 F•·g−1 at 20 A·•g−1, and excellent cycle stability with 92.7% of initial capacitance retained after 10000 cycles in 6 mol·•L−1 KOH aqueous electrolyte. This study provides a facile method for large-scale production of IGNSs from aromatic hydrocarbon molecules for use in high-performance energy storage devices.