The role of iodine in the enhancement of the supercapacitance properties of HI-treated flexible reduced graphene oxide film: an experimental study with insights from DFT simulations

Abstract

Herein, the effect of iodine on graphene frameworks is explored towards supercapacitance properties and the influence of iodine on graphene via p–p hybridization towards the enhancement of specific capacitance is presented with insights from quantum simulations. Here, we synthesized a reduced graphene oxide flexible film (RGO/FF) and reduced graphene oxide powder (RGO/P) by HI acid treatment and studied their electrochemical energy storage (supercapacitance) performance. The main feature of this study is that iodine remains in the graphene framework during the HI treatment and enhances the supercapacitance performance. The experimental characterizations and electro-chemical measurements reveal that the iodine remaining in the graphene framework contributes towards the pseudo-capacitance properties of reduced graphene oxide and enhances the supercapacitance performance. The specific capacitance increases from 73 F g⁻¹ in graphene to 122 F g⁻¹ in iodine-doped graphene films. RGO/P shows a higher capacitance value compared to RGO/FF due to the easy ion intercalation and the exposure of more surface area towards the access of charged species. We have performed state-of-the-art density functional theory (DFT) simulations to study the interactions and bonding mechanism of iodine on RGO surfaces and provide theoretical insights into the electronic properties for enhanced capacitance in iodine-doped RGO. Iodine is bonded to graphene with a favourable binding energy of −0.42 eV due to the interaction of the C 2p orbitals and I 5p orbitals. The enhancement in quantum capacitance due to iodine attachment justifies the enhancement in the specific capacitance of graphene.