This paper describes a facile, single-step hydrothermal method to prepare ruthenium sulfide/thermally reduced graphene oxide (RuS2/TRGO) nanocomposites. In this synthesis procedure, aqueous solutions of RuCl3, L-cysteine, and graphene oxide are employed as the metal, sulfur, and graphene sources, respectively. The chemical structures and morphologies of the nanocomposites are characterized by Xray diffraction, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy. Cyclic voltammetry, galvanostatic charge-discharge cycling, and electrochemical impedance spectroscopy are used to examine their electrochemical performances. The RuS2 nanoparticles (similar to 10 nm) uniformly disperse on the surfaces of the TRGO layers to form the RuS2/TRGO composite, which adequately inhibits aggregation of the RuS2 to fully exploit its impressive electrochemical activity and capacitance as a pseudocapacitive electrode material. The combination of the TRGO interconnected conductive networks and uniformly anchored RuS2 generates a specific capacitance of 193 F g(-1) at a 5 mV s(-1) scan rate, 150 F g(-1) at a 0.5 A g(-1) current density, good rate capability (57.3% retention at 6.25 A g(-1)), and reasonable cycle stability (90% retention of capacitance over 2000 cycles at a current density of 0.75 A g(-1)). Further, the RuS2/TRGO-30 composite electrode achieves energy densities of 20.84 and 6.11 Wh kg(-1) at power densities of 250 and 3666.7 W kg(-1), respectively. The RuS2/TRGO composites are promising for high-level energy storage applications because of their superior electrochemical activities. (c) 2018 Elsevier Ltd. All rights reserved.