Kinetics and mechanism of palladium electrodeposition on graphite electrode by impedance and noise measurements

The kinetics of palladium electrocrystallization from 0.01 M Pd(NH3)4Cl2, NH4Cl, and NH4OH bath (pH = 10) is studied by means of cyclic voltammetry (CV), impedance spectroscopy (EIS) and electrochemical noise (EN). Crossovers in cyclic voltammograms demonstrate that the deposition of palladium proceed via a nucleation/growth. A model for palladium deposition with multi-step mechanism is proposed to account for electrode kinetics. Electrodeposition mechanism takes place trough interfacial reactions with reaction intermediates. Parameters of impedance model in this system can be calculated from the fitting of experimental data to the Faradaic impedance function derived theoretically. With the aid of an equivalent circuit it is possible to determine the charge transfer resistance and the resistance and the capacity of lattice formation. The electrochemical noise is shown to originate from the random birth of edges and therefore birth rate of monolayers was obtained.

► Electrodeposition of palladium proceeds via a nucleation/growth mechanism.
► A model for palladium deposition with multi-step mechanism is proposed.
► Faradaic impedance function of model was derived.
► Kinetic parameters of model was calculated from the impedance function.