Graphene non-covalently functionalized with Gallic acid (Ga) as high performance electrode material for supercapacitors

Abstract

Organic small molecules are a very promising kind of materials in energy storage devices because they are green, low-cost and renewable resources. However, the poor electrical conductivity of organic molecules limits their using as electrode materials. The combination of organic molecules and conductive carbon material is a useful method to enhance their electrical conductivity. Here, Gallic acid (Ga) functionalized graphene hydrogel (GH) composite (Ga/GH) was synthesized by a simple hydrothermal method. The Ga/GH composite exhibits outstanding electrochemical capacitance performance because of the incorporation of the Faradaic pseudocapacitance of Ga and the double-layer capacitance of graphene hydrogel. The specific capacitance can reach up to 483 F g−1 at 1 A g−1. In addition, when the current density is increased to 100 A g−1, the rate capability is up to 64.2%. Meanwhile, a Ga/GH//DQ-RGO and a Ga/GH//AC asymmetric capacitor were assembled by using Ga/GH as the positive electrode and 2,6-diaminoanthraquinon functionalized graphene composite (DQ-RGO) and activated carbon (AC) as the negative electrode, respectively. The Ga/GH//DQ-RGO ASC provides an energy density of 27 Wh kg−1 along with a power density of 0.908 kW kg−1 and two such devices in series successfully can illuminate 26 red light-emitting diodes (LEDs). And the Ga/GH//AC ASC provides an energy density of 19.11 Wh kg−1. Two such devices in series can illuminate 20 red light-emitting diodes (LEDs).

Keywords

• Non-covalent modification
• Graphene hydrogel
• Organic molecules
• Gallic acid