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

In this work, RuO 2 honeycomb networks (RHCs) and hollow spherical structures (RHSs) were rationally designed and synthesized with modified-SiO 2 as a sacrificial template via two hydrothermal approaches. At a high current density of 20 A g –1, the two hierarchical porous RuO 2 · x H 2 O 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 (H 2 SO 4 ) and alkaline (KOH) electrolytes. As compared to RuO 2 bulk structure and similar RuO 2 counterpart reported in pseudocapacitors, the two hierarchical porous RuO 2 · x H 2 O frameworks have better energy storage capabilities, high-rate performance, and excellent cycling stability.