Transport corrections

Oxidation of Adsorbed CO The electro-oxidation of CO has been extensively studied given its importance as a model electrochemical reaction and its relevance to the development of CO-tolerant anodes for PEMFCs and efficient anodes for DMFCs. In this section, we focus on the oxidation of a COads monolayer and do not cover continuous oxidation of CO dissolved in electrolyte. An invaluable advantage of COads electro-oxidation as a model reaction is that it does not involve diffusion in the electrolyte bulk, and thus is not subject to the problems associated with mass transport corrections and desorption/readsorption processes. 

St.eadyr .t te Measurements. In order to obtain a more quantitative understanding of the process resulting in the inhibition of the 0 reduction reaction, Tafel measurements were made. The mass transport corrected Tafel equation [35] ... 

Figure 26 exhibits the polarization curves in terms of the cathode overpotential variation with current density for the CL27 obtained from the 3-D, single-phase DNS model prediction,25,27 the experimental observation25,27 and the liquid water transport corrected 1-D macrohomogeneous model.27 The polarization curve refers to the cathode overpotential vs. current density curve in the... 

Finally for effects where both the translocation and kinetic properties are important one can merge both models. This can be done by including the transport corrections in the kinetic model described here. In this case different transport rate functions result in different influx coefficients and, hence, different kinetic properties of the proteasome. This modeling approach is especially important for the... 

Fig. 17. Steady-state curves of oxygen reduction on perovskite oxide electrodes after mass transport correction using the RDE. a. LaNi03 O, La 7Sr 3Mn03 , LaojSrojCoCh [81],...

Fig. 4. Mass-transport-corrected Tafel piot for oxygen reduction at the Pt/Nafion interface measured with the system described in [4]. (Reprinted by permission of the Electrochemical Society).

Uribe et al. suggested that the only meaningfiil comparison between ORR rates obtained at various interfacial systems should be based on mass-transport-corrected ORR currents measured at a given cathode potential (as distinct from extrapolated). Such a comparison is shown in Table 3 for ft/ionomer and Pt/aqueous acid solution interfaces. 

In earlier attempts to study the ORR at the Pt/ionomer interface [82], a classical RDE configuration was used to control oxygen transport to a smooth Pt electrode coated by a recast film of Nafion. This configuration is required to complete the electrochemical cell by immersing the RDE in an aqueous electrolyte in which the other two electrodes are inserted, leaving some questions as to the possible effect of the liquid electrolyte on the measured interfacial rates. Results shown in Table 4, of mass-transport-corrected ORR currents at the bare Pt electrode and at the same RDE coated with a recast film of Nafion, indicate marginal enhancement of ORR rates at the lowest over potentials for the RDE coated with a recast film of Nafion. This marginal enhancement is noticeably smaller than... 

Work described in Ref. 86 includes a detailed investigation of the temperature dependence of ORR kinetic parameters at the Pt/bulk Nafion interface in the range from 30 to 90 °C. Plots of the log of mass-transport-corrected current density versus the potential of the Pt microelectrode showed an increase of a factor of about five in the rate of ORR at 0.90 V and about three at 0.85 V as the temperature was increased from 30 to 90 °C. The apparent activation energies for the two regions (low and high Tafel slope) were calculated from the dependence of the apparent exchange current density on T according to... 

Mass-transport-corrected currents at T = 30 °C, that is, the kinetic current densities evaluated from the measured T = 30 °C... 

Fig. 40 (a) ORR current, (b) kinetic (mass-transport-corrected) ORR current and (c) the... 

Spherical Harmonics Method. Wigner recognized that the diffusion theory approximation in all of these calculations was deficient. However, he was reluctant to invoke more complicated transport theory because the neutrons were not monoenergetic, and any transport correction to the diffusion theory would be obscured by the error caused by the assumption that the thermal neutrons were monoenergetic. He and Breit had used the spherical harmonics method in their original calculations of the size of a bomb, and he supervised the later work at Chicago on the application of the spherical harmonics expansion to calculate the thermal utilization. 

FIG. 1 Left side dependence of the norm, quantum yields for var. fluorescence, 5p and for PSII-photochemistry, 5pO i the pH of the inner-thyIdkoid space in isolated thylakoids, 5p was calculated from steady state e -transport, corrected for closed PS II centers, as in [1]. Bight side dependence of 5p of PS 11-part ides on the pH of the suspension medium. Particles were suspended... 

Moreover, the preceding statements remain true whether a simple hypothesis = 0 of zero flux on the boundary is used, or a transport correction is made, of the usual form... 

Fig. 17.4 Tafel plot of the applied potential, E (in the range 0.7 V > > 0.5 V), vs. log of the mass transport corrected current for the ORR in [demaliCFsSOs]. On the t -axis, i is the current at potential E and i l is the limiting current measured from the ORR polarisation curve. Reprinted from Walsh, D A Ejigu, A Smith, J Licence, P (2013) Phys. Chem. Chem. Phys. 15 7548-7554 with permission of the PCCP Owner Societies...

The assemblies GODIVA and JEZEBEL were chosen for the calculations the exact specifications used for these assemblies are given in Ref. 4. The calculations Were made with the DTF-I V code S, angular quadrature and Po transport-corrected cross sections were used. The 26-group structure, specified for the ENDF benchmark problems was used in these calculations. The LASL data were processed by the SIGMA code which is described In Ref. 3 the ENDP/B data were processed by the MC2 code. ... 

The reference treatment of scattering anisotropy was to use a transport correction to the total cross section and assume isotropic scattering (PI option of MC ). Support calculations by ORNL comparing the PI and P3 scattering options of ANISN for Assembly 48 gave negligible differences, thus defending the reference approach. 

FIGURE 13.13 Transport-corrected potentials for cathodes made with various loadings of 50 wt % PtA ulcan XC72 catalyst measured in 50cm -active-area fuel cells operating at 80°C,... 

The calculational method used in Step 6 is usually diffusion theory, often improved through the use of "transport corrections" of various sorts. Diffusion theory, as was previously mentioned, is the simplest neutron transport calculational method. It assumes a very low-order directional flux shape, which makes it inappropriate for use in problems that involve strong isolated sources or strong isolated absorbers. It is not accurate enough for Steps 3-5 because of fuel pin and control rods once these sources and absorbers have been "smeared" into the assembly cross sections that come from Step 5, diffusion theory is generally accurate enough for Step 6 full reactor calculations. 

Transport Corrects errors with lost and missed packets... 

Hydrogen Oxidation and Evolution on Platinum in Acids, Fig. 3 HOR polarization curve on a singleparticle microelectrode blue dots and line) obtained by Chen and Kucemak [3] on the left axis, mass-transport-corrected kinetic current on the right axis red circles) with fitted curve black line) using the dual-path kinetic equation [4, 8]... 

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