Haloplumbate salts as reagents for the non-aqueous electrodeposition of lead

Abstract

Cyclic voltammetry experiments on the Pb(II) salts, [PPh₄][PbX₃] (X = Cl, Br, I) in CH₂Cl₂ solution ([PPh₄]X supporting electrolyte) at a Pt disk electrode show reproducible nucleation and stripping features consistent with reduction to elemental Pb. The reduction potential shifts to less cathodic from Cl (−0.40 V) → Br (−0.27 V) → I (−0.19 V vs. Ag/AgCl), in line with the Pb–X bond strengths decreasing. Potentiostatic electrodeposition using [PPh₄][PbCl₃] in CH₂Cl₂ leads to growth of a thin film of crystalline Pb onto planar TiN electrodes, confirmed by SEM, EDX and XRD analysis. Electrodeposition under similar conditions onto a planar Au electrode leads to deposition of elemental Pb, accompanied by some alloying at the substrate/film interface, with XRD analysis confirming the formation of AuPb₂ and AuPb₃. Transferring the [PPh₄][PbCl₃] reagent into supercritical CH₂F₂ (17.5 MPa and 360 K) containing [PPh₄]Cl led to very limited solubility of the Pb reagent; using [NⁿBu₄]Cl as a supporting electrolyte caused an increase in solubility, although still lower than in liquid CH₂Cl₂. Cyclic voltammetry experiments (Pt disk) using this electrolyte also show voltammetry consistent with Pb deposition, however the low solubility of the lead salt in scCH₂F₂ meant that electrodeposition onto a planar TiN substrate was not possible.