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+0.3 V (vs. RHE). Many nuclei were created, however, in the potential region where hydrogen adsorption took place, i.e. more negative than +0.3 V. EQCM measurement showed that the surface mass was steadily increased during the potential scan as far as the cathodic current flowed even in the potential region where hydrogen adsorption took place. The abrupt surface mass decrease and increase were observed, however, when the potential was stepped from +0.4 V (hydrogen desorbed state) to +0.1 V (hydrogen adsorbed state) and from +0.1 to +0.4 V, respectively, showing the desorption and adsorption of PdC142− complex from the electrode surface upon hydrogen adsorption and desorption, respectively. These results support the model that the PdCl42− complex plays an important role to inhibit the three-dimensional growth and facilitate the two-dimensional growth.
doi:10.1016/S0022-0728(02)00643-5 
Copyright © 2002 Published by Elsevier Science B.V. All rights reserved.
Mechanism for nucleation and growth of electrochemical palladium deposition on an Au(111) electrode
Received 8 October 2001;
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Abstract
The initial kinetics of electrochemical deposition of palladium on an Au(111) electrode in 0.1 M H2SO4 solution containing K2PdCl4 have been investigated quantitatively by cyclic voltammetry (CV) and potentiostatic current transient measurements. A cathodic current maximum was observed in the initial stage of Pd deposition process in 0.1 mM K2PdCl4 solution. The analysis shows that the deposition of palladium in this solution proceeds by an instantaneous nucleation and two-dimensional (2D) growth mode. When the concentration of K2PdCl4 became higher, a potential-dependent cathodic current ‘plateau’ after the current maximum was observed. Simple nucleation-growth models cannot fit the transients in the region of the ‘current plateau’. The present current transient results were discussed in comparison with the results obtained by in situ scanning tunneling microscopy (STM).
Author Keywords: Electrodeposition; Underpotential deposition (upd); Au(111) electrode; Palladium; Cyclic voltammetry; Transient methods; Kinetics; Nucleation
