Effect of Oxygen Partial Pressure

In a similar maimer, we could isolate the contribution from oxygen as 

The change in voltage owing to a change in oxygen partial pressure from and Pqj while keeping P q and Pq unchanged is express as 

A direct methanol fuel cell (DMFC) uses liquid methanol (CH3OH) as fuel. The electrochemical half and overall reactions in a DMFC is summarized in Table 4.1. The overall reaction in a DMFC is given as 

The open circuit cell voltage based on the Nernst equation is given by Equation 4.48b as 

Enthalpy change caused by temperature change from T, = 298 K to Tj = 400 K  

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One feature of oxides is drat, like all substances, they contain point defects which are most usually found on the cation lattice as interstitial ions, vacancies or ions with a higher charge than dre bulk of the cations, refened to as positive holes because their effect of oxygen partial pressure on dre electrical conductivity is dre opposite of that on free electron conductivity. The interstitial ions are usually considered to have a lower valency than the normal lattice ions, e.g. Zn+ interstitial ions in the zinc oxide ZnO structure. 

Palozza, P, Luberto, C, Calviello, G, Ricci, P, and Bartoli, GM, 1997. Antioxidant and prooxidant role of beta-carotene in murine normal and tumor thymocytes Effects of oxygen partial pressure. Free Radic Biol Med 22, 1065-1073. 

Two types of catalysts have been proposed for the CPOM reaction copper and palladium. The catalytic properties of these materials show significant discrepancies with respect to by-product formation and the effect of oxygen partial pressure. The Cu-based catalysts display high selectivity for the CPOM reaction whereas for the Pd-based catalysts CO formation is significant. 

Tesoriere, L., DArpa, D., Re, R., and Livrea, M. A. (1997) Antioxidant reactions of all-trans retinol in phospholipid bilayers effect of oxygen partial pressure, radical fluxes, and retinol concentration. Arch Biochem Biophys 343, 13-8. 

Table 4.6.1 Effects of oxygen partial pressures (mmHg) on cultured cells ...

Figure 7 shows the effects of oxygen partial pressure on the isobutane oxidation over the H3PMol2O40(Py) catalyst. With the increase of the oxygen partial pressure, the conversion of isobutane increased greatly, and the selectivities to methacrylic acid and methacrolein decreased especially up to 14kPa. The selectivities to acrylic acid and acetic acid increased continuously with the increase of the partial oxygen pressure. 

The effect of oxygen partial pressure (P02) on the areal rates of ethane transformation at 648 K is shown in Figure 6. In the samples without potassium or with low substitution, the activity increased as P02 increased. However, in the sanq>les with x = 0.20-0.25, only little changes in the intrinsic rate of ethane conversion could be observed wdien P02 increased. Reaction orders... 

From Table 6.1, one can conclude that an oxide is labeled stoichiometric if A.X is a weak function of oxygen partial pressure. Conversely, an oxide is considered nonstoichiometric if the effect of oxygen partial pressure on the composition is significant. This concept can be better appreciated graphically as shown in Fig. 6.7. 

Figure 8. Schematic of the effect of oxygen partial pressure on the concentration of defects in a oxide growing via parabolic oxidation on a metal.

Effect of Oxygen Partial Pressure by Using Different Methanol Concentrations... 

Figure 5.10 A plot showing the effect of oxygen partial pressures, which are below the bulk dissociation pressure of CU2O, on the limiting thickness of the oxide layer (after Reference [4]).

Figure 15.17 Effect of oxygen partial pressure upon metal penetration of some common alloys by oxidation after exposure for one year at 930°C.

Wolfenstine J, Lee U, Poese B, Allen J (2005) Effect of oxygen partial pressure on the discharge capacity of LiCoP04. J Power Sources 144 226-230... 

K. Mukai, Z. Yuan, K. Nogi, and T. Hibiya, 2000, Effect of Oxygen Partial Pressure on the Surface Tension of Molten Silicon and Its Temperature Coefficient , ISIJ Int. 40, S148-S152. 

Figure 103. Effect of oxygen partial pressure P02 on the impedance characteristics of the Lao,8Sro,2Nio,4Feo.603.5 /Lag 83Si5Alo,75Feo,25 026 6 interface at 600 oC. Open circuit conditions, (a) Nyquist plot (b) -Zim vs. log(f) plot.. ...

Figure 105. Effect of oxygen partial pressure 02 P and temperature on the apparent polarization conductance Rp" of the Lao 8Sro,2Nio,4Feo,603.5 /La9.83Si5Alo.75Feo.25026 8interface. The values of the exponent n in equation Rp = kP"02 are shown in the figure for the different temperatures.

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