Iodine-steam doped graphene films for high-performance electrochemical capacitive energy storage

Recently, the fabrication of high-performance graphene films as electrode materials become a research tendency for flexible energy-storage devices. Here, we successfully prepare iodine-doped reduced graphene oxide (I-rGO) films with excellent capacitive performance by a simple and versatile technique of iodine steam doping. The iodine as an effective p-type dopant can enhance electrical conductivity of graphene films by charge transfer process, further improving capacitive performance of the devices. The electrochemical properties of as-prepared I-rGO films with different mass loadings are systematically and comprehensively studied. With the change of mass loading (1.5–6.7 mg cm−2), the gravimetric specific capacitance of I-rGO films remains almost invariable at the studied range of current density, and finally can reach ∼150 F g-1 at 0.2 A g−1. With the increasing mass loading, supercapacitors based on the I-rGO films show almost linear growth of areal specific capacitance at any current densities from 1 to 30 mA cm−2 (eventually reach ∼524 mF cm-2 at 1 mA cm−2). Additionally, we fabricate flexible all-solid-state supercapacitors, which also displays excellent areal specific capacitance (∼450 mF cm−2), great cycling stability and favorable electrochemical stability. These results indicate that the fabricated I-rGO films have great advantages as electrode materials for flexible energy-storage devices.