Nucleation and growth of Pd nanoparticles during electrocrystallization on pencil graphite

The aim of present study was to investigate the mechanism of palladium electrodeposition on a pencil graphite surface from an aqueous solution containing 1 mM PdCl2 and 500 mM H2SO4. Cyclic voltammetry revealed that the electrodeposition process proceeds via an initial underpotential deposition (UPD) and subsequently, it follows by the overpotential deposition (OPD) under diffusion control. Current transients showed a complex deposition trend, i.e. the electrodeposition of Pd includes at least three stages: adsorption on the surface, and two types of nucleation courses; two-dimensional (2D) and three-dimensional (3D) which limited by the lattice incorporation of Pd adatoms and the diffusion of Pd ions, respectively. Therefore the electrocrystallization of Pd on pencil graphite conforms to the Stranski–Krastanov growth mechanism. Furthermore, theoretical models were applied to evaluate each of above mentioned stages for different electrode potentials and to estimate the electrochemical parameters of Pd electrodeposition. The micrographs of electrodeposited Pd at relatively high frequency of the nucleation rate, illustrated a well dispersed Pd nanoparticles with a relatively narrow size distribution.

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► Pd nanoparticles deposition follows Stranski–Krastanov growth mechanism.
► The process includes three stages: adsorption, 2D and 3D nucleation.
► Each single Pd atom adsorbed on the nucleation site can grow spontaneously.
► A uniform distribution of Pd nanoparticles with average size of 33 nm was achieved.