Electrochemistry of PdCl2 at glassy carbon electrode in 1-Ethyl-3-methylimidazolium chloride ionic liquid

Abstract

Electrodeposition of palladium from ionic liquids has not been actively studied although this new class of electrolytes offer certain important advantages. Further, the application of rotating disc technique for kinetic studies in ionic liquids is scarce, and absent from the studies on Pd. In this work, the rotating disc electrode (RDE) technique was used to study the electrochemistry of PdCl2 dissolved in 1-ethyl-3-methylimidazolium chloride [EMIM][Cl] ionic liquid. Glassy carbon (GC) served as working electrode. The standard electrochemical techniques, such as cyclic voltammetry(CV), linear sweep voltammetry(LSV), chronopotentiometry(CP) and chronoamperometry(CP) were used under rotating and stationary conditions, at standard 100C. CV revealed two cathodic (C1 and C2) and two anodic (A1 and A2) current peaks. We are proposing that both cathodic current peaks belong to the same reduction of PdCl42− reaction, split into two by electrode surface morphology changes; C1 and C2 representing electroreduction of Pd on GC and Pd on Pd, respectively. The first anodic current peak (A1) is not well understood, but the second (A2) clearly distinguishes electrodissolution of Pd with thin film geometry. According to Levich and Levich-Koutecky analysis the first reduction step (C1) is the mixed kinetics, while the second (C2) is the mass transfer controlled. Diffusion coefficients estimated are of ~10−7cm2/s order.Concerning the stages of nucleation and growth of Pd, for the nucleation stage a 2D-instantatneous nucleation mechanism is proposed. The growth is aggregative, made of numerous Pd nanoclusters, consequently not fitting any of the 2D and 3D-growth models.