Hydroxyl standard reduction potentials

The hydroxyl radical is a powerful oxidant with a standard reduction potential of 2.73 V in acidic solution. In neutral solution where the free energy of neutralization of OH by the proton is not available, the reduction potential is calculated to be 1.9 V (Table 2). 

The catalytic properties of copper during polyols conversion in aqueous phase may be drastically modified by some additives. Metals having a standard oxido-reduction potential higher than that of copper (Ir, Rh, Ru, Pd, Pt, Au) can be deposited on it by oxido-reduction reaction. The first atoms of second metal deposited exchange with hydroxylated... 

Chloride ions will be discharged at a platinum, graphite or magnetite anode from saturated neutral solutions of sodium or potassium chloride rather than hydroxyl ions although at equilibrium conditions it should be the very opposite, as the reversible deposition potential (reduction potential) of oxygen in neutral solution is much lower ) (7Eoh- i o2. Pt = 0.815 V at 25 °C) than the standard... 

Fig. 2. Oxidation state diagram of oxygen at pH 7 at otherwise standard conditions (lmolal concentrations, 1 atm for gases). The x-axis gives the oxidation state, the y-axis the product of reduction potential and oxidation state. As such the slope represents the reduction potential. Adapted from ref. [4]. A compound that lies above a line joining its neighbours is unstable with respect to disproportionation, as is the case for superoxide and hydrogen peroxide. The line from hydrogen peroxide to the middle of the water-hydroxyl line represents the one-electron reduction potential of the couple H202/ 0H, H2O.

These equations refer to one-electron reductions versus the standard hydrogen electrode. Substrates M with more positive reduction potentials for the couple M/ M are stronger oxidants than substrates with lower or negative E. Therefore, in this case, M is easier to reduce. Eor example, the couple Cl /Cr has a reduction potential E of 2.200 to 2.600 V, and therefore chloride ions can theoretically be oxidized in water to chlorine atoms by hydroxyl radicals with E( OH, H / H20) = 2.730 V, according to Eq. 6-3 ... 

Of these products it is the three radical species which are the most reactive. The solvated electron and hydrogen atom have reduction potentials (Eo) of —2.87 and —2.30 V versus the standard hydrogen electrode (SHE), respectively [22], and hence they are extremely reactive reductants. The hydroxyl radical is a highly oxidising species with a reduction potential (Eo) of 2.65 V vs SHE [22]. 

An important feature of a corrosion process is the reduction of the dissolved oxygen by formation of hydroxyl ions (OH"). Since the equilibrium potential is linked through the concentration of the OH" ions with the concentration of the hydrogen ions with the (or H3O+ ions) by the ionic product of water (6 +)(fl jj ) = = 10 " at 25°C, the equilibrium potential is pH-dependent. The standard... 

The standard half-cell potential for the reduction of water to form hydroxyl ion in Table 9.1 is reported as —0.828 V. If instead we write the reaction ... 

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