Origin of the “Excursion Peak” during cycling voltammetry of Pb–Sn alloys

• Behavior of the excursion peak of lead–tin alloys was investigated.
• Cracks appear in the corrosion layer during the peak generation.
• Behavior in different experimental conditions supports cracks as origin of the peak.
• Tin influence on the peak is connected with its influence on the corrosion layer.

The behavior of the excursion peak in different experimental conditions for lead–tin alloys has been investigated. The appearance of cracks in corrosion layers during the excursion peak formation has been proven with SEM images. These fractures are believed to reveal the metallic lead which undergoes oxidation, causing the generation of the excursion peak. Influence of acid concentration, scan rate and temperature on the peak shape and potential shift was investigated. It has been concluded that the rate of excursion peak generation reaction is lower than the rate of lead dioxide reduction to lead sulfate. Increase in scan rate gives similar effects as decrease in acid concentration. Higher temperature greatly increases the excursion peak size. The tin content in Pb–Sn alloys has been shown to influence the peak, which is the biggest for 1% tin content. Described results have been found to be consistent with the assumed mechanism of corrosion layer cracking.