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Lead(IV) oxide, commonly called lead dioxide or plumbic oxide or anhydrous plumbic acid. sometimes wrongly called lead peroxide[citation needed is a chemical compound with the formula PbO2. It is an oxide where lead is in an oxidation state of +4; bond type is predominantly covalent. It is an odorless dark-brown crystalline powder which is nearly insoluble in water. It exists in two crystalline forms. The alpha phase has orthorhombic symmetry; it was first synthesized in 1941 and was identified in nature as a rare mineral scrutinyite in 1988. The more common tetragonal beta phase was first identified as the mineral plattnerite around 1845 and later produced synthetically. Lead dioxide is a strong oxidizing agent which is used in the manufacture of matches, pyrotechnics, dyes and other chemicals. It also has several important applications in electrochemistry, in particular in the positive plates of lead-acid batteries.

Applications

Lead dioxide is used in the production of matches, pyrotechnics, dyes and the curing of sulfide polymers. It is also used in the construction of high-voltage lightning arresters.

Lead dioxide is used as an anode material in electrochemistry. Beta-PbO2 is more attractive for this purpose than the alpha form because it has relatively low resistivity, good corrosion resistance even in low-pH medium, and a high overvoltage for the evolution of oxygen in sulfuric-acid- and nitric-acid-based electrolytes. Lead dioxide can also withstand chlorine evolution in hydrochloric acid. Lead dioxide anodes are inexpensive and were once used instead of conventional platinum and graphite electrodes for regenerating potassium dichromate. They were also applied as oxygen anodes for electroplating copper and zinc in sulfate baths. In organic synthesis, lead dioxide anodes were applied for the production of glyoxylic acid from oxalic acid in a sulfuric acid electrolyte.

The most important use of lead dioxide is the cathode of lead acid batteries. Its utility arises from the anomalous metallic conductivity of PbO2. The lead-acid battery stores and releases energy by shifting the equilibrium (a comproportionation) between metallic lead, lead dioxide, and lead(II) salts in sulfuric acid.

Pb + PbO2 + 2 HSO−
4 + 2 H+ → 2 PbSO4 + 2 H2O   E° = +2.05 V
Safety
Being a strong oxidant, lead dioxide is a poison when ingested. The associated symptoms include abdominal pain and spasms, nausea, vomiting, and headache. Acute poisoning can lead to muscle weakness, metallic taste, loss of appetite, insomnia, dizziness, with shock, coma and death in extreme cases. The poisoning also results in high lead levels in blood and urine. Contact with skin or eyes results in local irritation and pain.