embedded iron particles that are not directly involved in the oxygen reduction pathway. The high ORR activity and durability of catalysts involving this second site, as demonstrated in fuel cell, are attributed to the high densityof active sites and the elimination or reduction of Fenton-type processes. The latter are initiated byhydrogen peroxide but are known to be accelerated by iron ions exposed to the surface, resulting in the formation of damaging free-radicals.

We report a sonochemical synthesis of homogeneous PtCu 3 nanoparticles. Ultra-sonication during reduction in a non-aqueous solution is compared with synthesis under identical conditions in the absence of sonication (to form a Rieke alloy). X-ray diffraction (XRD) measurements suggest that the sonochemical procedure produces an amorphous, uniformly alloyed nanomaterial having a composition consistent with the PtCu 3 stoichiometry, while the Rieke alloy is polyphasic. Energy dispersive X-ray (EDX) analysis indicates that the composition of the sonochemically prepared PtCu 3 material reflects the nominal values. EDX and XRD analyses also provide evidence for the inhibition of oxide formation on sonochemically prepared PtCu 3 nanoparticles, but oxide is readily apparent in the Rieke alloy. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images of the sonochemically prepared sample show particles with diameters of $2 to 3 nm. As-synthesized PtCu 3 particles were activated using an electrochemical de-alloying procedure to prepare an oxygen reduction electrocatalyst. The de-alloyed catalyst consisted of a Pt-rich surface layer, over a core indicated as having a Pt 3 Cu composition. The de-alloyed sample exhibited $3 to 6 fold enhancements in oxygen reduction reaction (ORR) activity when compared to commercial Pt catalysts.

PtCo/C and Pt/C catalyst powders were incorporated into electrospun nanofiber and conventional sprayed cathode membraneelectrode-assemblies (MEAs) at a fixed electrode loading of 0.1 mg Pt /cm 2 . The binder for PtCo/C nanofiber cathodes and Pt/C nanofiber anodes was a mixture of Nafion and poly(acrylic acid) (PAA), whereas the sprayed electrode MEAs utilized a neat Nafion binder. The structure of electrospun fibers was analyzed by scanning transmission electron microscopy (STEM) and energy-dispersive X-ray spectroscopy (EDS), which showed that the fibers were ∼30% porous with a uniform distribution of catalyst and binder in the axial and radial fiber directions. The initial performance of nanofiber MEAs at 80°C was 20% better than the sprayed electrode MEA (a maximum power density of 1,045 mW/cm 2 vs. 869 mW/cm 2 ). The benefit of the nanofiber electrode morphology was most evident at end-of-test (after a metal dissolution accelerated stress test), where power densities dropped by only 8%, after 30,000 square wave voltage cycles (0.6 V to 0.95 V), as compared to a 35% drop in the maximum power for the sprayed electrode MEA. The use of a recovery protocol improved the initial performance of a nanofiber MEA by ∼13%, to 1,070 mW/cm 2 at 0.65 V, and increased the power after a metal dissolution stress test by 5-10% (e.g. 840 mW/cm 2 at 0.65 V after 30,000 voltage cycles). At rated power, the nanofiber MEA generated more than 1,000 mW/cm 2 at 99°C and a pressure of 250 kPa abs. The high performance and durability of PtCo/C nanofiber cathode MEAs is due to the combined effects of a highly active cathode catalyst and the unique nanofiber electrode morphology, where there is a uniform distribution of catalyst and binder (no agglomeration) and short transport pathways across the submicron diameter fibers (which lowers gas transfer resistance and facilitates water removal from the cathode).

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A simple, surfactant-free solvothermal method is reported for the preparation of <10 nm shape-controlled platinum crystallites. Reactions were carried out in N,Ndimethyformamide (DMF) and DMF−water mixtures. Effects of reaction time and temperature, DMF−water ratio, and metal precursor salt were examined. When the reaction conditions were tuned, ensembles of Pt particles with dominant truncated octahedral/ cuboctahedral or cubic shapes could be formed from the metal acetylacetonate (acac) precursor salt. Metal nanocrystal development was monitored through the use of highresolution transmission electron microscopy (HR-TEM) and X-ray and electrochemical analysis methods. Voltammograms probing CO and formic acid oxidation over shapecontrolled nanocrystals adsorbed to a glassy carbon electrode displayed expected features characteristic of extended ( 111) and (100) facets, confirming the stability and surface cleanliness of particles taken directly from the reaction mixture. A mechanism for Pt reduction and the growth and stabilization of preferentially shaped Pt nanocrystals in the DMF−water solvent system is proposed. The involvement of DMF as a reducing agent and carboxylate ions as weakly coordinating, and hence easily displaced, nanoparticle capping ligands is discussed.