Direct, Soft Chemical Route to Mesoporous Metallic Lead Ruthenium Pyrochlore and Investigation of its Electrochemical Properties

Mesoporous, nanocrystalline metallic lead ruthenium oxide (a pyrochlore) was synthesized through the formation of a mesostructured cohydroxide network via liquid crystal templating, and subsequent “soft” chemical oxidation that crystallizes the oxide at low temperature. The stable S + I – interaction chemistry responsible for the templating methodology is elucidated. The formation of a disordered mesoporous structure with a pore volume of 0.18 cm 3 /g and walls comprised of nanocrystallites was confirmed by X-ray diffraction and conductivity, N 2 isotherm measurements, and TEM observations. The resistivity of mesoporous oxide at room temperature was 0.046 Ω·cm, only 2 orders of magnitude less than the single crystal value, and one of the only two porous metallic oxides that are known to date. The electrocatalytic properties of this material for oxygen reduction and evolution in aqueous and nonaqueous media were evaluated by cyclic voltammetry, chronoamperometry, and linear sweep voltammetry. These techniques show that the synthesized pyrochlore lowers the overall oxidation voltage by 0.7 V relative to carbon in nonaqueous, Li + -containing electrolyte. This is the result of its ability to both completely oxidize Li 2 O 2 (at a relatively low potential) and electrocatalytically oxidize all known side-products formed from electrolyte decomposition in the Li–O 2 battery. This further helps to explain the nature of “electrocatalysis” in this system.