Design and Tailoring of the 3D Macroporous Hydrous RuO2 Hierarchical Architectures with a Hard-Template Method for High-Performance Supercapacitors.

In this work, RuO2 honeycomb networks (RHCs) and hollow spherical structures (RHSs) were rationally designed and synthesized with modified-SiO2 as a sacrificial template via two hydrothermal approaches. At a high current density of 20 A g-1, the two hierarchical porous RuO2·xH2O frameworks showed the specific capacitance as high as 628 and 597 F g-1; this is about 80% and 75% of the capacitance retention of 0.5 A g-1 for RHCs and RHSs, respectively. Even after 4000 cycles at 5 A g-1, the RHCs and RHSs can still remain at 86% and 91% of their initial specific capacitances, respectively. These two hierarchical frameworks have a well-defined pathway that benefits for the transmission/diffusion of electrolyte and surface redox reactions. As a result, they exhibit good supercapacitor performance in both acid (H2SO4) and alkaline (KOH) electrolytes. As compared to RuO2 bulk structure and similar RuO2 counterpart reported in pseudocapacitors, the two hierarchical porous RuO2·xH2O frameworks have better energy storage capabilities, high-rate performance, and excellent cycling stability.