A Facile and Green Synthesis of a MoO2-Reduced Graphene Oxide Aerogel for Energy Storage Devices.

Mara Serrapede,Marco Fontana,Marco Armandi,Arnaud Gigot,Paola Rivolo,Elena Tresso,Glenda Biasotto

doi:10.3390/ma13030594

Abstract

A simple, low cost, and “green” method of hydrothermal synthesis, based on the addition of l-ascorbic acid (l-AA) as a reducing agent, is presented in order to obtain reduced graphene oxide (rGO) and hybrid rGO-MoO2 aerogels for the fabrication of supercapacitors. The resulting high degree of chemical reduction of graphene oxide (GO), confirmed by X-Ray Photoelectron Spectroscopy (XPS) analysis, is shown to produce a better electrical double layer (EDL) capacitance, as shown by cyclic voltammetric (CV) measurements. Moreover, a good reduction yield of the carbonaceous 3D-scaffold seems to be achievable even when the precursor of molybdenum oxide is added to the pristine slurry in order to get the hybrid rGO-MoO2 compound. The pseudocapacitance contribution from the resulting embedded MoO2 microstructures, was then studied by means of CV and electrochemical impedance spectroscopy (EIS). The oxidation state of the molybdenum in the MoO2 particles embedded in the rGO aerogel was deeply studied by means of XPS analysis and valuable information on the electrochemical behavior, according to the involved redox reactions, was obtained. Finally, the increased stability of the aerogels prepared with l-AA, after charge-discharge cycling, was demonstrated and confirmed by means of Field Emission Scanning Electron Microscopy (FESEM) characterization.

Highlights

One of the key issues for future energy storage systems is to find new materials for highly efficient electrodes to be exploited in supercapacitors (SCs)
Field Emission Scanning Electron Microscopy (FESEM) images at different magnifications show that the morphology in both cases is comparable, as it is characterized by pores whose size ranges from the nanometer to the micrometer scale
At the nanoscale (Figure 1b), extremely wrinkled flakes are obtained by means of both the synthesis routes leading to high specific surface area (SSA) and accessibility by a liquid electrolyte, as the hydrothermal synthesis itself partially prevents the graphene sheets restacking

Summary

Introduction

One of the key issues for future energy storage systems is to find new materials for highly efficient electrodes to be exploited in supercapacitors (SCs). Reduced graphene oxide (rGO) has gained, in the last years, great attention due to the following advantages: It is produced by using inexpensive graphite as raw material through cost-effective chemical methods with a high yield [1]; It is highly hydrophilic and it can form stable aqueous colloids to facilitate the assembly of macroscopic structures, when subjected to specific procedures [2]. Due to strong bubbling during the N2 H4 or NaBH4 -mediated reduction process, the forming hydrogel is broken into pieces [16], confirming that the use of these two reagents is less preferable than the ethylendiamine (EDA) usage This synthesis of ultralight chemically converted graphene aerogels, characterized by high compressibility and excellent elasticity, was applied for energy dissipation and vibration damping. NaHSO3 , on the other hand, was successfully used for preparation of rGO based 3D architecture, but the resulting aerogel showed [10] an electrical conductivity and a C/O ratio lower than the HI mediated reduced material

Methods

Results

Conclusion