Bockris and Huq

V. This had been observed for the first time by Bockris and Huq [32], then by a few other groups. The same has also been observed on Rh electrodes, but Au, Pd, and Ir are unsuitable for such measurements, the rest potentials being mixed potentials [31]. 

EXAMPLE 12-2 According to Bockris and Huq the exchange current density for the oxygen electrode in acid solution is of the order of 10 A/cm on a platinum surface. The polarization resistance is RTIAFjo = 6 x 10 fl-cm. The double-layer capacity C j is of the order of 40 p/lcm, based on the true area, or perhaps 100 pjjcm based on the geometric or projected area, on which the current density was based. Thust = 6 X 10 X 100 X 10 = 6 x 10 s, and the time for overpotential decay from 10 to 1 mV is estimated to be 2.3t 4 h. Therefore, measurements accurate to... 

The Tafel equation also describes the evolution of oxygen at a platinum anode. Bockris and Huq found that, with solutions carefully purified by preelectrolysis, the oxygen electrode exhibits reversible behavior (E = 1.24 V, compared with the theoretical 1.23 V). The exchange current density, however, is only of the order of 10" to 10" °A/cm in dilute sulfuric acid so polarization occurs readily, and relatively large overpotentials are observed at moderate current densities. In solutions of ordinary chemical purity the Nemst relation fails for the oxygen electrode because of mixed-potential behavior. Criddle, using platinum electrodes in highly purified 1 M KOH, obtained a rest potential of 1.59 V. The potential is reduced by peroxide, which may be formed with impurities such as metals, protein, or carbon. 

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