Direct synthesis of electroactive mesoporous hydrous crystalline RuO2 templated by a cationic surfactant

Abstract

We describe a direct low-temperature, liquid crystal surfactant templating and crystallization route to form quasi-ordered crystalline mesoporous RuO₂·0.4H₂O. Our method constitutes a direct approach to the crystalline oxide, constructed of nanosized metal oxide building blocks that are assembled to form thin walls. This leads to high surface areas (up to 250 m² g⁻¹). In our approach, cationic surfactants (i.e., hexadecyl-trimethylammonium chloride, C₁₆TMA⁺ Cl ⁻) serve as pore-directing agents, which can participate in an indirect S⁺X⁻I⁺ interaction mediated by the chloride ion to coordinate a cationic ruthenium nitrosyl precursor. Gentle decomposition of the initially formed mesostructured metal cation–surfactant composite leads to crystallization of the wall structure. The promising electrochemical properties of porous RuO₂·xH₂O result from a more highly ordered structure and almost tripled surface area (190 m² g⁻¹) compared to that obtained from the nanocasting method. Crystalline mesoporous RuO₂·0.4H₂O exhibits high capacitance of 410 F g⁻¹ and good rate capability, whereas the amorphous mesoporous RuO₂·1.3H₂O displays capacitance over 700 F g⁻¹.