Standard reduction potentials for dioxygen

TABLE 9.3 Standard Reduction Potentials for Dioxygen Species in Water [02l 1 atm (1.0 mM>] (Formal Potentials for 02 at Unit Activity)... 

Figure 1 Standard reduction potentials for dioxygen species in water [1 atm O2, pH 7, V vs. NHE]...

Table 1 Standard reduction potentials for dioxygen species in water ...

The standard reduction potential for dioxygen to give water at 25 °C, 1 atm, and pH = 0 is E° =. 23 V. Substitution into the Nernst equation gives... 

Although reduction potentials may be estimated for half-reactions, there are limits for their values that correspond to both members of a couple having stability in an aqueous system with respect to reaction with water. For example, the Na+/Na couple has a standard reduction potential of -2.71 V, but metallic sodium reduces water to dihydrogen. The reduced form of the couple (Na) is not stable in water. The standard reduction potential for the Co3 + / Co2 + couple is +1.92 V, but a solution of Co3+ slowly oxidizes water to dioxygen. In this case the oxidized form of the couple is not stable in water. The standard reduction potential for the Fe3T/Fe2+ couple is +0.771 V, and neither oxidized form or reduced form react chemically with water. They are subject to hydrolysis, but are otherwise both stable in the aqueous system. The limits for the stability of both oxidized and reduced forms of a couple are pH dependent,... 

The standard reduction potentials for the main species formed by the Group 17 elements in aqueous solution are given in Tables 6.16 and 6.17, for pH values 0 and 14, respectively. Irrespective of the pH of the solution, the halogen elements range from the extremely powerful F2 (which has the potential to oxidize water to dioxygen), through the powerful oxidants Cl2 and Br2, to 12, which is a relatively weak oxidant. 

Table3.1 Standard reduction potentials for reactions of relevance to the two- and four-electron reduction pathways of dioxygen in acid and alkaline aqueous solutions.

TTHE COPPER(II) AND COPPER(I) IONS undergo facile redox interconversions for which the standard reduction potential is highly dependent on the nature of the ligands and coordination geometries observed (1). Thus, copper ion is a useful electron transfer or oxidation catalyst in the presence of dioxygen (02) (2-4). These properties have been put to advantage by nature, where copper-containing proteins (5-11) exist as electron... 

Fio. 1. standard oxidation-reduction potentials for the steps involved in the conversion of dioxygen to water at 25° and pH 7. 

The standard reduction potentials of the most relevant half-reactions involved in the four- and two-electron reduction of dioxygen in acid and alkaline aqueous media are listed in Table 3.1. It follows from these values, that, under full thermodynamic control, the equilibrium concentration of peroxide at the reversible potential for the four-electron reduction of oxygen in acid media, that is, 1.23 V, is of the order of 10 18 M. Hence, a stepwise reduction of dioxygen to yield currents of about 1A cm 2 will require values for the standard heterogeneous rate constants for... 

Standard potentials for the reduction of dioxygen to water via hydrogen peroxide (25 °C, 1 atm 0 fugacity)... 

Reduction potentials (V) for dioxygen species in aqueous solutions with O Caq) as standard state... 

While autoxidation is undesirable during storage, it Umits the environmental damage after spillage and is the driving force in hydrazine-air fuel cells, which have a standard potential of 1.56 V, which is split into 1.16 V for the oxidation of hydrazine (68) and 0.4 V for the reduction of dioxygen (69). 

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