Carbon Dot-Mediated Synthesis of Manganese Oxide Decorated Graphene Nanosheets for Supercapacitor Application

In this work, we demonstrate that carbon dots (CDs) can be used as a dispersing agent for graphene as well as a reducing agent for KMnO4 for the synthesis of manganese oxide (MnOx)-graphene hybrid nanocomposites for supercapacitor applications. CDs obtained from the pyrolysis of ammonium citrate under dry heating possess excellent solubility in water due to their oxygen- and nitrogen-containing functional groups. In addition, the sp(2)-carbon-rich CDs exhibited strong interaction with graphene through pi-pi stacking for self-immobilizing on graphene in the preparation of water-soluble CD/graphene nanocomposites (CDGs). Interestingly, MnOx could be grown in situ on CDGs after reaction with KMnO4 in aqueous solution under a mild reaction temperature (75 degrees C). Under the mild reaction conditions, CDs undergo sacrificial oxidation for the formation of MnOx nanoparticles on graphene, whereas the graphenes graphitic carbons are protected. The as-formed nanostructured MnOx on CDGs (MnOx-CDGs) was employed to fabricate flexible solid-state supercapacitor which exhibited good capacitance properties (specific capacitance similar to 280 F g(-1)) with very high charge-discharge cyclic stability (>10 000 cycles) and good capacitance retention at 90 degrees bending angle. Compared to other graphene-based nanocomposites, our one-pot synthesis route for MnOx-CDGs is relatively green, simple, rapid, and cost-effective and has a great potential for the synthesis of different metal oxide-decorated graphene nanocomposites for energy conversion and storage applications