In real life applications, supercapacitors (SCs) often can only be used as part of a hybrid system together with other high energy storage devices due to their relatively lower energy density in comparison to other types of energy storage devices such as batteries and fuel cells. Increasing the energy density of SCs will have a huge impact on the development of future energy storage devices by broadening the area of application for SCs. Here, we report a simple and scalable way of preparing a three-dimensional (3D) sub-5 nm hydrous ruthenium oxide (RuO2) anchored graphene and CNT hybrid foam (RGM) architecture for high-performance supercapacitor electrodes. This RGM architecture demonstrates a novel graphene foam conformally covered with hybrid networks of RuO2 nanoparticles and anchored CNTs. SCs based on RGM show superior gravimetric and per-area capacitive performance (specific capacitance: 502.78 F g(-1), areal capacitance: 1.11 F cm(-2)) which leads to an exceptionally high energy density of 39.28 Wh kg(-1) and power density of 128.01 kW kg(-1). The electrochemical stability, excellent capacitive performance, and the ease of preparation suggest this RGM system is promising for future energy storage applications.

X-ray photoelectron spectroscopy (XPS) characterization was performed to confirm the hydrous nature of the as-synthesized RuO2 nanoparticles. The survey XPS spectrum from our sample is provided in Figure S4. Although ruthenium is typically analyzed in XPS by following the strong singals from the 3d photoelectrons, here we used the 3p spectra instead in order to avoid interferences from the carbon substrates. The Ru 3p3/2 peak was deconvoluted into two components, which were identified with RuO2 (462.2 eV)46 and RuOH (464.1 eV). Those signals were found to exhibit an intensity ratio of 1 to 1.2 (Figure 3a). A similar ratio (1:1.3) is estimated from Ru-O-Ru, identified at 529.0 eV47, and Ru-O-H, centered at 530.2 eV (Figure 3b). The XPS data in the C 1s region (Figure 3c) is quite complex, showing a total of seven components including peaks assigned to the Ru 3d photoelectrons, at 280.8 eV (Ru 3d5/2 of RuO246, labeled A) and at 281.7 eV (a shake-up feature due to final state effects48, labeled B). The peak at 283.3 eV, labeled C, was assigned to RuOH. The C 1s peak at 285.0 eV, from our support, was used for binding energy calibration; the rest of the components come from Ru 3d3/2 photoelectrons.