Effect of temperature and atmosphere on the conductivity and electrochemical capacitance of single-unit-thick ruthenium dioxide

Wrapping a monoparticulate layer of 2-3-nm RuO2 around the fibers comprising porous SiO2 filter paper produces a conductive nanoshell in which similar to 90% of the RuO2 units are surface-sited, creating the equivalent of a supported single-unit layer of the oxide. The room temperature electronic conductivity, normalized for the dimensions of the total RuO2(SiO2) object, increases with calcination temperature reaching a maximum of 830 mS cm(-1) for a 200 degrees C-calcined paper, and then sharply decreases at higher temperatures as the nanoparticles in the ultrathin RuO2 shell ripen and disrupt the connectivity. The calcination temperature also influences the electrochemical capacitance, which is optimized at 150 degrees C with a RuO2-normalized specific capacitance of 850 F g(-1). Calcining the RuO2(SiO2) papers to temperatures >= 250 degrees C reduces the electrochemical capacitance due to structural ordering and ripening of the RuO2 nanoparticles composing the coating. The electrochemical capacitance and the magnitude of the electronic conductivity of the RuO2(SiO2) paper are unaffected by exposure to air, humidified air. Ar, humidified Ar, or methanol-saturated Ar at 25 degrees C. Exposing the papers at room temperature to either pure H-2 or humidified H-2 significantly reduces the pseudocapacitance and electronic conductivity. X-ray photoelectron spectroscopy confirms reduction of the RuO2 to Ru and scanning electron microscopy demonstrates shrinkage-induced stress cracking and disruption of the H-2-reacted nanoscale coating. These results indicate that the RuO2(SiO2) architecture can serve as a rugged, inexpensive, and conductive gas-diffusion scaffold for the design of a carbon- and ionomer-free anode for direct methanol fuel cells. (C) 2010 Elsevier B.V. All rights reserved.