Six Pt-Ru/carbon fiber nanocomposites have been prepared by using a bimetallic precursor as a source of metal. Carbon fiber supports include singled-walled nanotubes, multiwalled nanotubes, or graphitic carbon nanofibers having either platelet, wide herringbone, or narrow tubular herringbone atomic structures. Preparative procedures have been optimized to enhance the performance of these nanocomposites as anode electrocatalysts in direct methanol fuel cells. Pt-Ru nanoparticles are the major metal-containing component of these nanocomposites along with variable amounts of Ru metal. A range of direct methanol fuel cell performance is observed with a Pt-Ru/narrow tubular herringbone graphitic carbon nanofiber nanocomposite showing the highest performance. This performance is equivalent to that recorded for an unsupported Pt-Ru colloid at an anode catalyst loading of 2.7 mg total metal/cm 2 , but 64% greater than that of the unsupported Pt-Ru colloid at a lower catalyst loading of 1.5 mg/cm 2 .

Multistep deposition and reactive decomposition of a precursor molecule containing one Pt and one Ru atom on herringbone graphitic carbon nanofibers (GCNFs) affords a Pt-Ru/GCNF nanocomposite containing Pt-Ru alloy nanoclusters widely dispersed on the GCNF support. The nanocomposite has a total metal content of 42 wt % with a bulk Pt/Ru atomic ratio of ca. 1:1, and metal alloy nanoclusters having average particle sizes of 6 nm as calculated from XRD peak widths or 7 nm as measured directly from TEM images. XRD and electrochemical analysis of the nanocomposite as-prepared and stored under ambient conditions reveals the presence of small amounts of Ru metal and oxidized metal species. Comparative testing of this nanocomposite and an unsupported Pt-Ru colloid of similar surface area and catalyst particle size as anode catalysts in a working direct-methanol fuel cell (DMFC) reveals a 50% increase in performance for the Pt-Ru/GCNF nanocomposite. More detailed study of the catalytic performance of metal alloy/GCNF nanocomposites as DMFC anode catalysts appears to be warranted.

Thin films able to sustain an efficient photoreduction of Ag+ ions with 350 nm photons in air were prepared by crosslinking poly(vinyl alcohol) with glutaraldehyde in the presence of poly(acrylic acid). Standard colloid techniques served as screening methods for the selection of polymer compositions yielding films with desired properties. When present at high concentrations, Ag+ ions were reduced at room temperature in the films by poly(vinyl alcohol) but poly(acrylic acid) inhibited the slow dark reaction. Optical signals with maxima above 400 nm resulted from both reduction processes. The available evidence confirmed that they originated from nanometer-sized metal particles and is inconsistent with results for other proposed chromophores. An additional absorption centered at 280 nm that formed only under illumination was assigned to Ag3 + clusters. Small Ag crystallites with similar size distributions and with an average diameter of 5 nm were the main product of the photoreduction in non-crosslinked or crosslinked films. Larger particles were detected less frequently, and in the former films they consisted predominantly of crystallite aggregates. These results along with the long-term stability of the photogenerated Ag3 + clusters are consistent with a particle nucleation process based on diffusion and coalescence of mobile metal atoms in the films.