ISSN 1023-1935, Russian Journal of Electrochemistry, 2006, Vol. 42, No. 4, pp. 381–392. © MAIK “Nauka /Interperiodica” (Russia), 2006. Original Russian Text © A.V. Rudnev, E.B. Molodkina, A.I. Danilov, Yu.M. Polukarov, J.M. Feliu, 2006, published in Elektrokhimiya, 2006, Vol. 42, No. 4, pp. 432–444. 381 INTRODUCTION The processes of adsorption and electrochemical nucleation of metals on foreign substrates are of applied and fundamental importance [1–3]. Studying them is of pressing moment, for the modification of electrode surfaces with nanosize objects (monolayers, islet films, quantum dots, and conductors) is a major field of development in electrochemical nanotechnol- ogy. The process of copper electrocrystallization with multistep discharge of ions is extensively used in the industry and is of interest as a model system in studies of complex electrochemical processes. Initial steps of copper electrodeposition on various electrodes have been explored rather comprehensively ([1–22] and references therein). Our research into the mechanism of formation of adatom layers and nucle- ation of copper on polycrystalline Pt electrodes and sin- gle-crystals of Pt(hkl) and Au(111) [10–22] demon- strated that specific adsorption of oxygen-containing compounds (copper oxides, hydroxide ions, sulfate anions, hydrogen peroxide reduction products) on the positively charged surface of platinum electrodes accel- erates the reduction of copper ions, adsorption of ada- toms, and three-dimensional nucleation; it also exerts an influence on the concentration of copper(I) ions in the processes of discharge and ionization of copper. Adsorption of acetonitrile (AcN) on platinum was explored rather thoroughly with the aid of cyclic volta- mmetry and various kinds of spectroscopy. Acetonitrile is relatively stable on smooth polycrystalline platinum in a broad range of potentials [23]; it is frequently used as an organic aprotic solvent when studying the struc- ture of the electrical double layer (EDL) on assorted electrodes, the kinetics and mechanism of charge trans- port and the mechanism of electrochemical reactions [24–30]. On the platinum surface, chemisorbed acetonitrile may come in contact with the substrate through an elec- tron pair of the nitrogen atom (position I) or when two atoms (carbon, nitrogen of the CN group) are in contact with two platinum atoms (position II) [27, 31]. The lat- ter position is more probable at potentials that are more negative than the potential of zero charge (PZC). Increasing the potential leads to reorientation of mole- cules of AcN into position I and its additional adsorp- tion. As far as the estimates of the authors of [27] go, the PZC for Pt(111) and Pt(100) in acetonitrile is equal to ~0.25 V (NHE). Kinetics of Underpotential Deposition and Nucleation of Copper on the Pt(111) Face in the Presence of Acetonitrile A. V. Rudnev, a E. B. Molodkina, a A. I. Danilov, a, z Yu. M. Polukarov, a and J. M. Feliu b a Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Leninskii pr. 31, Moscow, 119991 Russia b Institute of Electrochemistry, University of Alicante, Alicante, Spain Received November 18, 2005 Abstract—The kinetics of underpotential deposition, three-dimensional nucleation, and growth of copper deposits at cathodic overpotentials on a Pt(111) electrode in solutions containing 0.5 M H 2 SO 4 , 10 mM CuSO 4 , and 0–200 mM acetonitrile (AcN) is studied by the cyclic voltammetry, potentiostatic current transients, and scanning probe microscopy methods. At low volume concentrations of acetonitrile ([AcN] ≤ 4 mM), adsorbed acetonitrile molecules accelerate the formation of a co-adsorption lattice of copper adatoms with anions due to local electrostatic effects at the charged interface. At higher concentrations, the underpotential deposition pro- cess is hampered, but the desorption of copper adatoms occurs at potentials more positive than those at low ace- tonitrile concentrations. This effect is attributed to a stabilizing action of acetonitrile molecules situated on the layer of copper adatoms and, in part, on platinum. At [AcN] = 0.4–40 mM, adsorbed acetonitrile molecules accelerate the growth of the bulk copper deposit, but the nucleation stage is hindered. The dependence of the copper amount on the deposition potential at [AcN] = 40 mM exhibits a maximum at 0.15–0.17 V. This effect was previously observed in weakly acid solutions (pH 1.7–3.0) containing no acetonitrile. The maximum rate of the deposit growth corresponds to an optimum number of crystallites (which is not too great) and an optimum distance between the growing centers in conditions of mixed kinetics “diffusion + electron transfer.” A substan- tial number of complexes Cu(I)–AcN forms at high acetonitrile concentrations. DOI: 10.1134/S102319350604015X Key words: copper, Pt(111), adsorption, nucleation, acetonitrile z Corresponding author, email <danilov@phyche.ac.ru>