The oxygen reduction reaction (ORR) has been studied on polycrystalline Pt3Ni and Pt3Co alloys in acid electrolytes using the rotating ring disk electrode (RRDE) method. Preparation and characterization of alloy surfaces were performed in ultrahigh vacuum (UHV). Clearly defined surface composition was determined via low-energy ion-scattering (LEIS) spectroscopy. Polycrystalline bulk alloys of Pt3Ni and Pt3Co were prepared in UHV having two different surface compositions:  one with 75% Pt and the other with 100% Pt. The latter we call a “Pt-skin” structure and is produced by an exchange of Pt and Co in the first two layers. The base voltammetry in 0.1 M HClO4 solution of the 75% Pt alloy surface indicated a decrease of Hupd pseudocapacitance (ca. 30−40 μC/cm2) consistent with the surface composition determined in UHV. With the exception of the “Pt-skin” surface on Pt3Ni, all the alloy electrodes exhibited stable i−E curves with repeated cycling between 0.05 and 1.0 V at all temperatures. Activities of Pt-a...

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Surface Composition Effects in Electrocatalysis: Kinetics of Oxygen Reduction on Well-Defined Pt3Ni and Pt3Co Alloy Surfaces

Hybridomas are finding increased use for the production of a wide variety of monoclonal antibodies. Understanding the roles of physiological and environmental factors on the growth and metabolism of mammalian cells is a prerequisite for the development of rational scale-up procedures. An SP2/0-derived mouse hybridoma has been employed in the present work as a model system for hybridoma suspension culture. In preliminary shake flask studies to determine the effect of glucose and glutaminE, it was found that the specific growth rate, the glucose and glutamine metabolic quotients, and the cumulative specific antibody production rate were independent of glucose concentration over the range commonly employed in cell cultures. Only the specific rate of glutamine uptake was found to depend on glutamine concentration. The cells were grown in continuous culture at constant pH and oxygen concentration at a variety of dilution rates. Specific substrate consumption rates and product formation rates were determined from the steady state concentrations. The specific glucose uptake rate deviated from the maintenance energy model1 at low specific growth rates, probably due to changes in the metabolic pathways of the cells. Antibody production was not growth-associated; and higher specific antibody production rates were obtained at lower specific growth rates. The effect of pH on the metabolic quotients was also determined. An optimum in viable cell concentration was obtained between pH 7.1 and 7.4. The viable cell number and viability decreased dramatically at pH 6.8. At pH 7.7 the viable cell concentration initially decreased, but then recovered to values typical of pH 7.1–7.4. Higher specific nutrient consumption rates were found at the extreme pH values; however, glucose consumption was inhibited at low pH. The pH history also influenced the behavior at a given pH. Higher antibody metabolic quotients were obtained at the extreme pH values. Together with the effect of specific growth rate, this suggests higher antibody production under environmental or nutritional stress.

A kinetic analysis of hybridoma growth and metabolism in batch and continuous suspension culture: Effect of nutrient concentration, dilution rate, and pH

Oxygen reduction reaction on Pt(111): effects of bromide

https://digital.library.unt.edu/ark:/67531/metadc881228/m2/1/high_res_d/917341.pdf

Surface segregation effects in electrocatalysis: kinetics of oxygen reduction reaction on polycrystalline Pt3Ni alloy surfaces

Submitted to the Journal of Electroanalytical Chemistry, November 6, 2002 Surface Segregation Effects in Electrocatalysis: Kinetics of Oxygen Reduction Reaction on Polycrystalline Pt Ni Alloy Surfaces** V. Stamenkovic*, T.J. Schmidt - , P.N. Ross and N . M . Markovic Materials Sciences Division, Lawrence Berkeley National Laboratory University of California at Berkeley, CA 94720, USA Abstract Effects of surface segregation on the oxygen reduction reaction (ORR) have been studied on a polycrystalline Pt Ni alloy in acid electrolyte using ultra high vacuum (UHV) surface sensitive probes and the rotating ring disk electrode (RRDE) method. Preparation, modification and Depending on the characterization of alloy surfaces were done in ultra high vacuum (UHV). preparation method, two different surface compositions of the Pt Ni alloy are produced: a sputtered surface with 75 % Pt and an annealed surface (950 K ) with 100 % Pt. The latter surface is designated as the Pt-skin structure, and is a consequence of surface segregation, i.e., replacement of N i with Pt atoms in the first few atomic layers. Definitive surface compositions were established by low energy ion scattering spectroscopy (LEISS). The cyclic voltammetry of the Pt-skin surface as well as the pseudcapacitance in the hydrogen adsorption/desorption potential region is similar to a polycrystalline Pt electrode. Activities of ORR on Pt Ni alloy surfaces were compared to polycrystalline Pt in 0.1M H C l O electrolyte for the observed temperature range of 293 Pt Ni (75% Pt) > Pt with the maximum catalytic enhancement obtained for the Pt-skin being 4 times

Surface segregation effects in electrocatalysis: Kinetics of oxygen reduction reaction on polycrystalline Pt3Ni alloy surfaces

https://onlinelibrary.wiley.com/doi/pdf/10.1002/bit.260200114

I. Adler

Papers

Solubility of oxygen in electrolyte solutions