structure-property relationships of nanostructured Ru/carbon aerogel composite materials have been evaluated. These new materials were prepared via a novel two-step metal vapor impregnation method which enables one to control the Ru loading through repetition of the process. The resulting microstructure is characterized by highly dispersed Ru particles (approximate to 20-30 A in diameter) attached to the carbon aerogel surface and distributed homogeneously throughout the material; the open pore structure of the carbon aerogels remains largely unaffected. Electrochemical characterization indicates that it is possible to increase the specific capacitance of the carbon aerogels in 1.0 M H2SO4 from approximate to 100 F/g to greater than 250 F/g for samples with > 50 wt % Ru due to the pseudocapacitive properties of hydrous RuO2. A volumetric capacitance greater than 140 F/cm(3) was observed for some samples. In addition, these materials show good cycling characteristics. Electrochemical impedance spectroscopy was unable to distinguish between double-layer capacitance and pseudocapacitance in these materials.