A reduced graphene oxide modified metallic cobalt composite with superior electrochemical performance for supercapacitors

Abstract

In this work, a unique reduced graphene oxide modified metallic cobalt (rGO/Co) composite, in which Co nanoparticles are in situ anchored on rGO sheets, has been synthesized via a facile one pot co-precipitation approach. Such a composite exhibited an impressive performance when used in (asymmetric) supercapacitors. For comparison purposes, pure rGO and Co were also prepared and investigated. Microscopic observation techniques, nitrogen sorption analysis and electrochemical methods etc. were used to characterize the materials' properties. The physical characterizations revealed rGO/Co possessed a “particle on sheet” structure with a “point to face” electronic contact between these two components, and the size of Co was much smaller than pure Co due to the geometric confinement of rGO, as well as a larger Brunauer–Emmett–Teller (BET) surface area resulting from the structural synergistic effect for alleviating the agglomeration of each component. Remarkably, the rGO/Co composite displayed the best electrochemical performance among the three synthesized samples with a capacity as high as 882.7 F g⁻¹ at a current density of 2 A g⁻¹ and presented a high rate capability as well. Moreover, an asymmetric supercapacitor using rGO/Co as positive active material and activated carbon (AC) as negative active material has also been fabricated and tested in the potential window ranging between 0 and 1.6 V, which was demonstrated to be able to achieve a maximum energy density of 40.7 W h kg⁻¹ at a power density of 1585.0 W kg⁻¹ as well as excellent rate capability and outstanding cycling durability.