Reference oxygen concentration

Here, it is reasonable to define the reference oxygen concentration as the oxygen concentration at the CCL GDL interface. The reference proton concentration on the surface of the agglomerate is determined by the type of ionomer, in particular its lEC, and the volume portion of ionomer with which the CCL is impregnated. For an orientation, a typical value is cgf 0.5 mol r. ... 

Here j x) is the local proton current density, is the volumetric exchange current density (the number of charges produced in unit volume per second, A cm ), c is the molar concentration of oxygen, Cref is the reference oxygen concentration, (f> is the conversion function, r] is the local polarization voltage, at is the proton conductivity of the CCL, D is the effective oxygen diffusion coefficient and jo is the cell current. 

Oxygen transfer rate (OTR) The product of volumetric oxygen transfer rate kj a and the oxygen concentration driving force (C - Cl), (ML T ), where Tl is the mass transfer coefficient based on liquid phase resistance to mass transfer (LT ), a is the air bubble surface area per unit volume (L ), and C and Cl are oxygen solubility and dissolved oxygen concentration, respectively. All the terms of OTR refer to the time average values of a dynamic situation. 

Chlorine-enhancement may offer a partial solution. The addition of the chlorinated olefin TCE, PCE, or TCP to air/contaminant mixtures has recently been demonstrated to increase quantum yields substantially [1, 2, 6]. We recently have extended this achievement [3], to demonstrate TCE-driven high quantmn efficiency conversions at a reference feed concentration of 50 mg contaminant/m air not only for toluene but also for other aromatics such as ethylbenzene and m-xylene, as well as the volatile oxygenates 2-butanone, acetaldehyde, butsraldehyde, 1-butanol, methyl acrylate, methyl-ter-butyl-ether (MTBE), 1,4 dioxane, and an alkane, hexane. Not 1 prospective contaminants respond positively to TCE addition a conventional, mutual competitive inhibition was observed for acetone, methanol, methylene chloride, chloroform, and 1,1,1 trichloroethane, and the benzene rate was altogether unaffected. 

The balance between relative rates of aerobic respiration and water movement were considered in Section 4.3.4. We saw that a subsurfece concentration minimum, the oxygen minimum zone (OMZ), is a common characteristic of vertical profiles of dissolved oxygen and is produced by in situ respiration. Waters with O2 concentrations less than 2.0 ppm are termed hypoxic The term anoxic is applied to conditions when O2 is absent. (Some oceanographers use the term suboxic to refer to conditions where O2 concentrations fall below 0.2 ppm but are still detectable.) As illustrated by Figure 4.21b, this water column is hypoxic in the OMZ. The dissolved oxygen concentrations are presented as % saturations in Figure 4.21c. With the exception of the mixed layer, the water column is undersaturated with respect to dissolved oxygen with the most intense undersaturations present in mid-depths. Surface supersaturations are the result of O2 input from photosynthesis and bubble injection. 

Whatever the initial step of formation of surface silyl radicals, the mechanism for the oxidation of silicon surfaces by O2 is expected to be similar to the proposed Scheme 8.10. This proposal is also in agreement with the various spectroscopic measurements that provided evidence for a peroxyl radical species on the surface of silicon [53] during thermal oxidation (see also references cited in [50]). The reaction being a surface radical chain oxidation, it is obvious that temperature, efficiency of radical initiation, surface precursor and oxygen concentration will play important roles in the acceleration of the surface oxidation and outcome of oxidation. 

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