Oxygen reduction reaction density

A sheet of steel of thickness 0.50 mm is tinplated on both sides and subjected to a corrosive environment. During service, the tinplate becomes scratched, so that steel is exposed over 0.5% of the area of the sheet. Under these conditions it is estimated that the current consumed at the tinned surface by the oxygen-reduction reaction is 2 X 10 A m -. Will the sheet rust through within 5 years in the scratched condition The density of steel is 7.87Mg m . Assume that the steel corrodes to give Fe " ions. The atomic weight of iron is 55.9. 

If, however, it is assumed from Eq. (2-40) that the protection current density corresponds to the cathodic partial current density for the oxygen reduction reaction, where oxygen diffusion and polarization current have the same spatial distribution, it follows from Eq. (2-47) with = A0/7 ... 

Karlberg GS, Rossmeisl J, Nprskov JK. 2007b. Estimations of electric field effects on the oxygen reduction reaction based on the density functional theory. Phys Chem Chem Phys 37 5158-5161. 

Eligh performance liquid chromatography Density functional theory Oxygen reduction reaction Rotating disk electrode Rotating ring disk electrode... 

The most important electrokinetic data pertinent to fuel cell models are the specific interfacial area in the catalyst layer, a, the exchange current density of the oxygen reduction reaction (ORR), io, and Tafel slope of ORR. The specific interfacial area is proportional to the catalyst loading and inversely proportional to the catalyst layer thickness. It is also a strong function of the catalyst layer fabrication methods and procedures. The exchange current density and Tafel slope of ORR have been well documented in refs 28—31. 

In practice, in all fuel cells that involve the utilization of 02 from air (Section 13.4.5), the oxygen reduction reaction [Eqs. (13.4) and (13.24)] is always rate determining for terrestrial applications. One can seejust how important it is to attempt to develop electrocatalysts for the cathodes of fuel cells on which the enhanced current density is high and Tafel slope is low and the efficiency of energy conversion, therefore, maximal. The direct relation of the mechanism of oxygen reduction and the associated Tafel parameters to the economics of electricity production and transportation is thus clearly seen. 

Figure 24 Schematic polarization data for oxygen reduction reaction (ORR) in neutral (pH 7.2) solution. Diffusion-limited current density (i L) is present due to mass transport limitations on dissolved oxygen.

Therefore let us instead consider the more practical case of the tertiary current distribution. Based on the dependency of the Wagner number on polarization slope, we would predict that a pipe cathodically protected to a current density near its mass transport limited cathodic current density would have a more uniform current distribution than a pipe operating under charge transfer control. Of course the cathodic current density cannot exceed the mass transport limited value at any location on the pipe, as said in Chapter 4. Consider a tube that is cathodically protected at its entrance with a zinc anode in neutral seawater (4). Since the oxygen reduction reaction is mass transport limited, the Wagner number is large for the cathodically protected pipe (Fig. 12a), and a relatively uniform current distribution is predicted. However, if the solution conductivity is lowered, the current distribution will become less uniform. Finite element calculations and experimental confirmations (Fig. 12b) confirm the qualitative results of the Wagner number (4). 

Figure 16 shows the steady-state limiting current density, ilim, for the oxygen reduction reaction (ORR) on pure Al, pure Cu, and an intermetallic compound phase in Al alloy 2024-T3 whose stoichiometry is Al20Cu2(Mn,Fe)3 after exposure to a sulfate-chloride solution for 2 hours (43). The steady-state values for the Cu-bearing materials match the predictions of the Levich equation, while those for Al do not. Reactions that are controlled by mass transport in the solution phase should be independent of electrode material type. Clearly, this is not the case for Al, which suggests that some other process is rate controlling. 

As discussed above, if the exchange current density of anode hydrogen oxidation is i nMc =0,1 Acni 2 and that of the cathode oxygen reduction reaction (ORR) is... 

Hyman, M.P., Medlin, J.W. Mechanistic study of the electrochemical oxygen reduction reaction on Pt(lll) using density functional theory. J. Phys. Chem. B 2006,110,15338-44. 

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