The polarization behavior of platinum and iridium In 2PbO · SiO2 melts was investigated between 850° and 900°C using cyclic voltammetry and current-reversal chronopotentiometry. With respect to a Pb|2PbO · SiO2 reference potential, the melt decomposed anodically at 0.64V in agreement with reported values obtained from two electrode measurements. Under anodic polarization, the evolution of O2 increased exponentially. Platinum oxidized to form PtO2 and iridium oxidized to form IrO2 and, what is believed to be, Pb2Ir2O7-x. The reactions involving PtO2 occurred at potentials in excess of its equilibrium Pt|PtO2 potential whereas reactions of IrO2 were very close to the Ir|IrO2 potential. An approximate value for the free energy of formation of Pb2Ir2O7-x was estimated to be −310 kJ/mol at 900°C which is consistent with conditions of its synthesis in air. The redox behavior of Pb|Pb2+ metal on Pt and Ir was equivalent to that of a reversible lead electrode. Lead alloyed with platinum to form a liquid (Pt, Pb) solution and solid Pt3Pb.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Renewable Energy, Sustainability and the Environment
- Surfaces, Coatings and Films
- Materials Chemistry