Photoelectrochemical Properties of the Lead Electrode during Anodic Oxidation in Sulfuric Acid Solution

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During oxidation of a lead electrode in a H₂SO₄ solution at potentials between–200 and +900 mV (vs. Hg/Hg₂SO₄ electrode) an anodic layer containingtet-PbO and PbSO₄ is formed. When oxidation is conducted in thedark, PbO does not display photoelectrochemical properties. In order to constitutea photoelectrochemical system the electrode has to be photoactivated byillumination with a given quantity of light at potentials more positive than0 mV. In this case the PbO layer converts into a PbO_n layer with 1 < n < 2.When a photoactivated electrode is illuminated three types of photoelectrochemicalprocesses occur. The first type leads to photoionization of lead oxideand OH_ad and O_ad are evolved at the PbO_n/solution interface. These processestake place at potentials between –400 and 0 mV. The second kind occurs atpotentials more positive than 0 mV and leads to the formation of PbO_n andphotoactivation of the oxide. The mechanism according to which these processestake place includes the formation of Pb⁴⁺ ions in the oxide via photochemicalreactions, reconstruction of the unit cell of PbO into that of PbO₂containing oxygen vacancies, and reactions of these vacancies with water withthe subsequent formation of PbO_n. The third kind of photoprocesses leads tophotolysis of water at the surface of the PbO_n layer with formation of O₂.

©1977 The Electrochemical Society, Inc.