Enhanced supercapacitor performance based on 3D porous graphene with MoO 2 nanoparticles
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Three dimensional (3D) porous graphene decorated with MoO2 nanoparticles were successfully synthesized by hydrothermal method and characterized by SEM and TEM, x-ray diffraction, Raman spectra, x-ray photoelectron spectroscopy, nitrogen adsorption–desorption analysis and electrochemical experiments. The results revealed that the in situ formed monoclinic MoO2 nanoparticles were randomly decorated on the surface of graphene sheets and the obtained graphene–MoO2 nanohybrids were 3D porous structures. The mass ratio of molybdenum precursor with GO has effects on the specific surface area and the electrochemical properties of the nanocomposite. The M30G1 (the mass ratio of molybdenum precursor with GO was 30:1) composite electrode exhibited a higher specific capacitance and better cycling stability. The specific capacitances were 356 F/g at the current density of 0.1 A/g in KOH electrolyte, which predicted their potential application in energy storage. The electrochemical performance of M30G1 composite was also investigated in Na2SO4 electrolyte, which was poorer than that in KOH electrolyte. Therefore, the chosen of electrolyte is important to materials performance.
I. INTRODUCTION
Supercapacitors are one of the most promising electrochemical energy-storage systems because of their ability for delivering higher power density than batteries/fuel cells and storing higher energy density than conversional electrostatic capacitors.1,2 Graphene has been widely used as the electrode materials of electrical double-layer capacitors, due to its unique properties such as superior electrical conductivity, excellent mechanical flexibility, larger surface area, and high thermal and chemical stability.3,4 However, due to the strong p–p interactions between graphene sheets, 2D structures easily agglomerated and restacking. This drawback hinders potential applications of graphene materials in electrochemical electrodes. One method to solve this problem is to incorporate spacer such as transition metal oxides into graphene sheet to form new nanostructure.5–9 Many transition metal oxides have been chosen as electrode materials to increase the storage performance of pseudocapacitors, such as RuO2, NiO, Fe2O3, V2O5, MoO3 and SnO2.10–15 Among these candidates, molybdenum oxides are relatively cheap pseudocapacitor materials with high theoretical capacitance, and have attracted many attentions.13,14,16–19 MoO2 has been extensively investigated as an electrode material due to high theoretical capacity Contributing Editor: Lan M. Reaney Address all correspondence to these authors. a) e-mail: [email protected] b) e-mail: [email protected] DOI: 10.1557/jmr.2016.438
(838 mA h/g) and excellent electronic conductivity (.1 104 S/cm).17,20–22 Giardi et al., synthesized polycrystalline nanoparticles of MoO2 on the surface of reduced graphene oxide and improved specific capacitance of 381 F/g at a scan rate of 0.5 mV/s.16 Duan et al., demonstrated a novel hierarchical core–shell structure pseudocapacitor of ZnO nanorod/NiO/MoO2 nanosheet ar
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