Outer oxygen reduction

The disbonding rate decreases with time [35], which can be attributed to the consumption of OH" ions by reaction with adhesive groups. This consumption is obviously partly compensated for by the formation of OH" ions through oxygen reduction these permeate inward from the outer surface of the coating. If this permeation is hindered by an aluminum foil gas seal, the disbonding rate falls off... 

Anderson AB, Alhu TV. 1999. Ah initio determination of reversible potentials and activation energies for outer-sphere oxygen reduction to water and the reverse oxidation reaction. JAm Chem Soc 121 11855-11863. 

In this notation, anodic current is positive, while cathodic current is negative. As the later section on oxygen reduction will show, the Tafel slope can change with overpotential. This is because the Butler-Volmer law only applies to outer-sphere reactions. Although it can describe electrode reactions, the equation does not account for repulsive interactions of the adsorbates or changes in the reaction mechanism as potential is changed. 

Corrosion current density — Anodic metal dissolution is compensated electronically by a cathodic process, like cathodic hydrogen evolution or oxygen reduction. These processes follow the exponential current density-potential relationship of the - Butler-Volmer equation in case of their charge transfer control or they may be transport controlled (- diffusion or - migration). At the -> rest potential Er both - current densities have the same value with opposite sign and compensate each other with a zero current density in the outer electronic circuit. In this case the rest potential is a -> mixed potential. This metal dissolution is related to the corro-... 

In the context of the present discussion, it is worth noting that virtually all the experimental systems that exhibit such "anomalous temperature-dependent transfer coefficients are multistep inner-sphere processes, such as proton and oxygen reduction in aqueous media [84]. It is therefore extremely difficult to extract the theoretically relevant "true transfer coefficient for the electron-transfer step, ocet [eqn. (6)], from the observed value [eqn. (2)] besides a knowledge of the reaction mechanism, this requires information on the potential-dependent work terms for the precursor and successor state [eqn. (7b)]. Therefore the observed behavior may be accountable partly in terms of work terms that have large potential-dependent entropic components. Examinations of temperature-dependent transfer coefficients for one-electron outer-sphere reactions are unfortunately quite limited. However, most systems examined (transition-metal redox couples [2c], some post-transition metal reductions [85], and nitrobenzene reduction in non-aqueous media [86]) yield essentially temperature-independent transfer coefficients, and hence potential-independent AS orr values, within the uncertainty of the double-layer corrections. 

Anderson and Albu investigated an outer-sphere oxygen reduction with ab initio calculations, whereby the electrode was assumed to not directly interact with the intermediate species. They proposed four one-electron transfer steps involving proton transfer from the electrolyte as ... 

Open-circuit decay of potential, 363, 374 Outer Helmholtz plane, 196 Overpotenlial, 101, 106 Oxygen evolution, 172 Oxygen, solubility in water, 155 Oxygen reduction, 175... 

For processes without outer current the following processes may be considered including oxygen reduction ... 

The Fe(II) oxidation occurs near the outer face of the cytoplasmic membrane, whereas oxygen reduction occurs on the inner face of the membrane. The electrons donated from Fe(II) oxidation are accepted by rusticyanin in the periplasm, followed by a transfer of electrons to cytochrome c... 

ITR may be joined by simultaneous ETR, without direct participation of the substrate and the oxide. For example, the anodic current density of Reaction (2) may be supplied from an outer circuit, but alternatively it may be compensated by cathodic currents such as hydrogen evolution or oxygen reduction at open-circuit conditions ... 

There are many examples of the way in which differential aeration combines with passivation to produce difficult corrosion problems. Figure 9.9 illustrates the case of crevice corrosion. The outer flat surface receives a plentiful supply of oxygen and hence passivates to produce a large protected area where oxygen reduction can... 

Ramaswamy N, Mukerjee S (2011) Influence of inner-and outer-sphere electron transfer mechanisms during electrocatalysis of oxygen reduction in alkaline media. J Phys Chem C 115 18015-18026... 

---