Formation of Palladium Complex at Carbon Paste Surface in Chloride Solution as Studied by Cyclic Voltammetry

Abstract

The deposition and dissolution of palladium at non-modified carbon paste electrode (CPE) is studied by cyclic voltammetry in chloride solutions (c ≥ 0.5 M KCl and pH 3 to 6). The Pd0 is deposited from tetrachloropalladate solution by potential cycles from E ≥ 0 V (vs Ag/AgCl) or positive potentials up to -0.5 V or by potentiostatic treatment at E ≤ 0 V. Oxidation peaks appear during potential sweep to positive direction after the preceding deposition of Pd. The appearance of two anodic peaks depends mainly on the amount of Pd0 deposited. The peak at about +0.1 V is caused by the dissolution of a palladium mono- or submonolayer, whereas the oxidation peak at more positive potentials is attributed to the dissolution of Pd from a palladium multilayer. After palladium deposition and potential sweep to positive potentials E > +0.8 V (or potentiostatic treatment at E > +0.8 V), a cathodic peak appears at about 0 V and corresponding anodic peak at +0.1 V. It is concluded that these peaks are caused by reduction and oxidation of the chloropalladate surface complex formed during preceding application of anodic potentials. Reaction schemes of PdII/Pd0 and chloropalladate complex are discussed.