Superior Additive of Exfoliated RuO₂ Nanosheet for Optimizing the Electrode Performance of Metal Oxide over Graphene

An effective way to optimize the electrode performance of metal oxide was developed by employing exfoliated 2D RuO₂ nanosheet as a conducting additive. The exfoliated RuO₂ nanosheet was easily incorporated into the Li–MnO₂ nanocomposite via a simple mixing of exfoliated RuO₂ and MnO₂ nanosheets, followed by the restacking with Li⁺ ions. The incorporation of RuO₂ nanosheet was found to be quite effective in increasing the surface area of the restacked Li–MnO₂ nanocomposite. The obtained heterolayered Li–MnO₂–RuO₂ nanocomposites delivered much greater specific capacitances than do the pristine Li–MnO₂ and Li–RuO₂ nanocomposites. Considering the fact that the RuO₂ nanosheet has higher electrode activity than the MnO₂ nanosheet, the greater specific capacitance of Li–MnO₂–RuO₂ nanocomposite than that of Li–RuO₂ strongly suggests that the incorporation of a small amount of RuO₂ nanosheet into the restacked Li–MnO₂ nanocomposite induces a synergistic improvement in its electrode activity. Of prime importance is that the Li–MnO₂–RuO₂ nanocomposites showed somewhat better electrode performances than the reduced graphene oxide (rG-O)-incorporated Li–MnO₂–rG-O homologues, attributable to more efficient charge transport and pore structure upon RuO₂ incorporation. The hydrophilic RuO₂ nanosheet is more effective in making a stronger chemical interaction with hydrophilic MnO₂ and also in depressing the self-aggregation of nanosheets compared to hydrophobic rG-O nanosheet. The present study clearly demonstrates that the RuO₂ nanosheet can be used as a better additive for improving the electrode performance of metal oxides compared with widely used rG-O.