The electrocapacitive properties of graphene oxide reduced by urea

We report a facile and green route to reduce graphite oxide using urea as the reducing agent. UV-Vis, XRD and XPS results revealed that urea was an effective reducing agent in removing oxygen-containing groups from graphite oxide for restoring the conjugated electronic structure of graphene. The obtained reduced graphene oxide was tested as supercapacitor electrode. Gravimetric capacitances of 255 and 100 F g−1 at current densities of 0.5 and 30 A g−1, respectively, were observed. The reduced graphene oxide paper showed a volumetric capacitance of 196 F cm−3. After 1200 continuous cycles of galvanostatic charge–discharge, the electrode retained 93% of its capacitance. The electrocapacitive performance of the urea-reduced graphene oxide outperformed most of the previously reported graphene-based electrode materials, which were reduced by hydrazine or NaBH4. The present reduction method holds great promise for mass production of soluble graphene-based materials for electrochemical energy storage.