Electrochemical oxygen reduction behavior of selectively deposited platinum atoms on gold nanoparticles.

Carbon-supported Pt@Au "core-shell" nanoparticles with varying surface concentration of platinum atoms have been synthesized using a novel redox-mediated synthesis approach. The synthesis technique allows for a selective deposition of platinum atoms on the surface of prefabricated gold nanoparticles. Energy dispersive spectroscopic analyses in a scanning electron microscope reveal that the platinum to gold atomic ratios are close to the nominal values, validating the synthesis scheme. X-ray diffraction data indicate an un-alloyed structure. The platinum to gold surface atomic ratio determined from cyclic voltammetry and copper under-potential deposition experiments reveal good agreement with the calculated values at low platinum concentration. However, there is an increase in non-uniformity in the deposition process upon increasing the platinum concentration. Koutecky-Levich analysis of the samples indicates a transition of the total number of electrons transferred (n) in the electrochemical oxygen reduction reaction from two to four electrons upon increasing the surface concentration of platinum atoms. Furthermore, the data indicate that isolated platinum atoms can reduce molecular oxygen but via a two-electron route. Moreover, successful four-electron reduction of molecular oxygen requires clusters of platinum atoms.

Anodic oxidation and molecular structure: influence on performance of normal saturated hydrocarbons in fuel cells.

Variation in the rate of anodic oxidation of normal saturated hydro carbons (at current densities of half the maximum value or higher) with the carbon number parallels the variation in the rate of diffusion (in electrochemical equivalents) of the hydrocarbon through the electrolyte. This parallelism, not previously recognized, is consistent with the concept of diffusion-influenced anode eactions. The conditions under which this behavior is expected are presented.

Purification and preparation of some caesium compounds.

Several methods for the purification and preparation of caesium compounds are described. Thermogravimetric data are presented for caesium oxalate and caesium carbonate.

Food Consumption of the Free-Living Aquatic Nematode Pelodera chitwoodi.

A Cartesian diver respirometer was used to measure O uptake and respiratory quotients at 25 C. Respiratory quotients were about 0.70 in starved nematodes, and 0.80 in third-stage and adult nematodes that had fed on bacteria. The energy output as measured by O uptake was inversely related to the concentration of bacteria in the medium, indicating reduction in feeding effort. Feeding bacteria to third-stage nematodes in divers quickly resulted in peak respiration rates averaging 6.4 nl O/mug wet weight nematode per hour (QO) or six times the endogenous rate. In about 4 hr, the rates fell and then stabilized at a QO of 2.5. Adult males fed bacteria in divers had a peak QO of 2.8 or twice the starved rate. Adult females fed bacteria had a peak QO of 3.7. Starving adult males and third-stage larvae were estimated to lose 2.4% and 1.4%, respectively, of their body weight per day in the form of fat based on the caloric equivalent o f oxygen used and a respiratory quotient of 0.70. The caloric content of the bacteria fed to nematodes in divers was determined. It was then calculated that both third-stage larvae and adult males ingested bacteria equivalent to 4.4 x 10 cal/mug wet weight nematode tissue per hour when feeding. Of the bacterial calories ingested, the larvae used 27% and adults 21% for respiration. It was estimated that males ingested 3.1 x 10 bacteria and females 10 x 10 bacteria during an 8-day life span.

Pathogenicity of the Lesion Nematode, Pratylenchus brachyurus, on Six Soybean Cultivars.

Pathogenicity tests of Pratylenchus brachyurus on selected greenhouse-grown soybean cultivars indicated the nematode reduced seed yield of 'Hood' but not that of 'Custer', 'Bragg', 'Dyer', or 'Pickett'. Root weights of all cultivars were reduced. Damage and numbers of nematodes within soybean roots growing at 13, 21, and 29 C were greater at higher temperatures. At 29 C, root pruning was prominent in 'Hood' and 'Pickett' but limited in 'Custer' and 'Hill'. Root pruning was not observed at 13 C and only 'Pickett' showed pruning at 21 C. Plant height and foliage weight were not affected. P. brachyurus had no effect on the emergence of 'Pickett' or 'Bragg' soybeans. Nematode counts from roots of 'Pickett' at intervals after inoculation indicated that hatching of second generation second-stage larvae occurred about 15 days after egg laying. An average of 68% of the initial inoculum penetrated the roots within five days of inoculation, the highest observed was 81% in five days. Details of structural damage in penetrated tissues were studied in sectioned roots. In soybean roots infected by P. brachyurus and/or Rhizoctonia solani greater damage occurred with nematode and fungus combined than with either acting alone.

Electrochemical in situ reaction cell for X-ray scattering, diffraction and spectroscopy.

A versatile electrochemical in situ reaction cell for long-term hard X-ray experiments on battery electrodes is described. Applications include the small-angle scattering, diffraction and absorption spectroscopy of lithium manganese oxide electrodes.