Anchoring Hydrous RuO2 on Graphene Sheets for High‐Performance Electrochemical Capacitors

Hydrous ruthenium oxide (RuO₂)/graphene sheet composites (ROGSCs) with different loadings of Ru are prepared by combining sol–gel and low‐temperature annealing processes. The graphene sheets (GSs) are well‐separated by fine RuO₂ particles (5–20 nm) and, simultaneously, the RuO₂ particles are anchored by the richly oxygen‐containing functional groups of reduced, chemically exfoliated GSs onto their surface. Benefits from the combined advantages of GSs and RuO₂ in such a unique structure are that the ROGSC‐based supercapacitors exhibit high specific capacitance (～570 F g^?1 for 38.3 wt% Ru loading), enhanced rate capability, excellent electrochemical stability (～97.9% retention after 1000 cycles), and high energy density (20.1 Wh kg^?1) at low operation rate (100 mA g^?1) or high power density (10000 W kg^?1) at a reasonable energy density (4.3 Wh kg^?1). Interestingly, the total specific capacitance of ROGSCs is higher than the sum of specific capacitances of pure GSs and pure RuO₂ in their relative ratios, which is indicative of a positive synergistic effect of GSs and RuO₂ on the improvement of electrochemical performance. These findings demonstrate the importance and great potential of graphene‐based composites in the development of high‐performance energy‐storage systems.