Mixed ionic–electronic conduction and electrochemical behavior of the lead and molybdenum ions in the lead–molybdate–germanate glasses

The structure, ionic conduction and electrochemical performance of a lead–molybdate–germanate glass with the 10MoO3 ∙ 90[7GeO2 ∙ 3PbO] composition were studied by means of cyclic voltammetry, electrochemical impedance spectroscopy, FTIR, UV–Vis and EPR spectroscopy. The cyclic voltammogram exhibits three distinct maxima attributed to the reduction of Ag+ 1 to Ag0, Mo+ 5 to Mo+ 4 and Pb+ 2 to Pb0. Nyquist diagram of the complex impedance shows two semicircles which appear in the high and small frequency region and a smaller arc in the intermediate frequency domain corresponds to the Warburg diffusion or/and mass transport impedance of the cell. Analyzing the Nyquist plots of the complex impedance for different silver nitrate electrolyte solution was found good sensing properties of these cells.Spectroscopic data investigations on glass after cyclic voltammetry show some modifications such as: i) the number of [PbO4] and [MoO6] structural units increases; ii) molybdenum ions appear in the different valence states (Mo+ 3, Mo+ 4, Mo+ 5, Mo+ 6).Our results suggest a mixed ionic–electronic conduction process and a larger mobility of the ions species in the glasses. Then, the modifier lead and molybdenum ions are able to migrate under an applied electric field and are responsible for mixed ionic–electric conduction in ternary molybdenum–lead–germanate glasses.

► The oxidation/reduction processes at the glass/silver nitrate interface
► Molybdenum and lead ions exist in glass in more valence states.
► After cyclic voltammetry some Mo+ 6 ions convert to Mo+ 5 ions.