Functionalized graphene aerogel with p-phenylenediamine and its composite with porous MnO₂: investigating the effect of functionalizing agent on supercapacitive performance

Graphene aerogel has emerged as a promising material for supercapacitors very recently. It is expected that functionalization of graphene aerogels can further improve their capability. Hence, in this study, functionalized graphene aerogel was synthesized via the interaction between graphene oxide and p-phenylenediamine as a functionalizing agent. The composites of functionalized graphene aerogel/MnO₂ and unfunctionalized graphene aerogel/MnO₂ were prepared by solution-phase deposition of MnO₂ nanoparticles into the functionalized and unfunctionalized graphene aerogel structures. Structural characterizations revealed that functionalization of composite with p-phenylenediamine led to increase in surface area. Morphological characterization revealed porous structure for functionalized graphene aerogel and flower-like microsphere for MnO₂. Supercapacitive performance of the composite was investigated by cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance spectroscopy. Fast Fourier transform continues cyclic voltammetry measurements were also used to study the cyclic stability of the supercapacitor electrodes. Functionalized graphene aerogel/MnO₂ displayed enhanced supercapacitive performance in 0.5 M Na₂SO₄ compared with unfunctionalized graphene aerogel/MnO₂, including high energy density of 26.2 Wh kg⁻¹ (at the power density of 1000 W kg⁻¹), excellent cycle life by showing 94 % capacitance retention after 5000 cycles, and high synergic effect. These results demonstrate that p-phenylenediamine as a functionalizing agent has considerable impact on enhancing supercapacitive performance of composite.