Pressure oxygen overvoltage

Iron (d=7.S gm/cm ) corrodes in a solution of pH 7.0 saturated with oxygen. The corrosion potential estimated for partial pressure of oxygen of 1 atm is —0.07 V vs. SHE. The oxygen overvoltage follows the relation ... 

Any factor which tends to decrease the velocity of Reaction 2, i.e., which increases the overvoltage, will decrease the corrosion represented by Reaction 1. Watts and Whipple have found that, contrary to statements in the chemical literature, a decrease of the external pressure will produce a decrease of corrosion of metals in adds. These workers, however, attribute the decreased corrosion to the absence of air in the solutions which were under reduced pressure. As it seemed probable to us that the effect is, largely at least, due to an increase in the overvoltage with decreased pressure, we repeated their experiments, taking care to exdude oxygen from the add. Table 1, which contains TABLE 1... 

PEM fuel cell characteristics are generally described with polarization curves. The thermodynamic equilibrium potential of the hydrogen/oxygen reaction is reduced by various overvoltage terms that depend on mass transport, kinetic, and ohmic phenomena within cell. In other words, the output voltage of a single cell is attributable to different current, temperature, and pressure dependant factors [1]. 

The standard reversible potential of this reaction is =-2.213 V at 970 C [2]. On an inert anode the anode product would be pure oxygen, so the anode potential (provided zero overvoltage) would be 2.213 V positive to an aluminium electrode. On a carbon anode the oxygen will react with carbon, and the partial pressure of oxygen will be much reduced and so would the anode potential. For the case of unit activity of alumina, the Nemst equation simply relates anode potential and oxygen partial pressure ... 

FIGURE 10.10. Semipermeability overvoltage of a platinum electrode used in an oxygen gauge. P and P f arc the pressures of the analyzed gas and the reference gas, respectively. (Data from Fouletier, J., Fabry, P., and Kleitz, M., J. Electrochem. Soc., 1976, 123, 204-213. With permission.)... 

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