Oxide-oxide galvanic displacement reactions: Effect of the concentration of the ions released by the sacrificial oxide

Abstract

• Effect of ions released in oxide-oxide galvanic displacement reactions was studied. • Displacement between PbO 2 and Mn 2+ or Co 2+ were used as model reactions. • Secondary mixed oxides produced at higher [Pb 2+ ] were richer in Pb. • Other effects of [Pb 2+ ] on secondary oxide growth depended on divalent cation. Galvanic displacement reactions between a solid oxide and a dissolved metal cation are interesting processes for the preparation of oxide nanoparticles or electrocatalytic layers consisting of secondary mixed oxides. Their mechanism is not yet fully clarified. The composition of the secondary mixed oxides and their growth rate depend on many physical and chemical variables. In the present study, we have focused on the effects of the concentration of the ions released from the sacrificial oxide to the solution, when they are intentionally added to reaction media. We have studied the displacement of sacrificial PbO 2 by either Mn 2+ or Co 2+ cations in acetate solution that contained variable concentrations of Pb 2+ , using electrochemical methods, SEM-EDS and XPS. The evolution of the open circuit potential of the systems was monitored during the reactions. We have found that, for both divalent cations, increasing concentrations of Pb 2+ ions in the acetate solutions caused the formation of mixed oxides richer in Pb. Effects on growth rate and equilibrium potential were different for Mn 2+ and Co 2+ .