✍ Scribed by J.W. Schultze; K.J. Vetter
No coin nor oath required. For personal study only.
Potentiostatic and galvanostatic pulse measurements were carried out to investigate the anodic oxygen evolution at platinum electrodes in IN I&SO4 in dependence on the oxide layer thickness d and the electrode potential F. The thickness d (1 .%I0 A) was obtained from cathodic charging curves. Further, the temperature dependence (0"~81°C) was evaluated from Bowden's measurements. Summarizing. the current ioz follows the relation, log i = A -(E." -aF$/2.3 RT-d/d,. Theexperimental activation energy E, = E." -aF7 decreases linearly with increasing overvoltage 7. The linear decrease of log i with increasing d, which is given by the term d/do, is correlated to the probability of the quantum mechanical tunnel transition of the electron from adsorbed ions, OH, or 0:~ respectively, through the oxide layer to the metal. Similar effects of the oxide layer thickness
on the current density were observed in the case of the oxygen evolution at iridium, the CO-oxidation on platinum, and the reduction of Cl-and Ce4+ at platinum. In these cases a rate determining electron transfer through the oxide layer is also assumed.
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