Hydroiodic Acid Reduced Graphene Hybrid with δ-MnO₂for Electrode Material in Supercapacitors

In this paper, we report a method for the further reduction of the low-cost graphene (LG) via hydroiodic acid to synthesize graphene hybrid with varying content of δ-MnO2. Scanning electron microscope (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD) were implemented to characterize the surface and structural properties of the reduced graphene (LGHI) and graphene-MnO2 composites (GM). It can be observed that the thickness of LGHI layers is about 10∼200 nm and as-prepared GM composites have a uniform morphology possessing a honeycomb structure. XRD results indicate that MnO2 in the GM exists as a δ-crystallographic structure of low crystallinity. Cyclic voltammetry (CV) curves, galvanostatic charge/discharge (GDC) curves and electrochemical impedance spectroscopy (EIS) were utilized in a three-electrode system to systematically investigate the electrochemical performance of varying δ-MnO2 content materials. Results reveal that once the mass fraction of δ-MnO2 in GM reaches 93.1% (labeled GM-6), the specific maximum capacitance of GM was found to be 783 F/g, 496 F/g, 345 F/g and 210 F/g at a current density of 0.3 A/g, 1 A/g, 3 A/g and 10 A/g, respectively. Moreover, GM-6 maintains almost 94.5% of its original specific capacitance after 5000 continuous cycles of charge-discharge. These promising results demonstrate that GM-6 has great potential to be utilized as an electrode material for supercapacitor applications.