Formation of Pb(III) Intermediates in the Electrochemically Controlled Pb(II)/PbO2 System

The formation of lead dioxide PbO2, an important corrosion product in drinking water distribution systems with lead-bearing plumbing materials, has been hypothesized to involve Pb(III) intermediates, but their nature and formation mechanisms remain unexplored. This study employed the electrochemical (EC) method of rotating ring disk electrode (RRDE) and quantum chemical (QC) simulations to examine the generation of intermediates produced during the oxidation of Pb(II) to PbO2. RRDE data demonstrate that PbO2 deposition and reduction involves at least two intermediates. One of them is a soluble Pb(III) species that undergoes further transformations to yield immobilized PbO2 nanoparticles. The formation of this intermediate in EC system is mediated by hydroxyl radicals (OH center dot), as was evidenced by the suppression of intermediates formation in the presence of the OH center dot scavenger para-chlorobenzoic acid. QC simulations confirmed that the oxidation of Pb(II) by OH center dot proceeds via Pb(III) species. These results show that Pb(III) intermediates play an important role in the reactions determining transitions between Pb(II) and Pb(IV) species and could impact lead release in drinking water.