A Generalized Electrochemical Aggregative Growth Mechanism

Abstract

The early stages of nanocrystal nucleation and growth are still an active field of research and remain unrevealed. In this work, by the combination of aberration-corrected transmission electron microscopy (TEM) and electrochemical characterization of the electrodeposition of different metals, we provide a complete reformulation of the Volmer-Weber 3D island growth mechanism, which has always been accepted to explain the early stages of metal electrodeposition and thin-film growth on low-energy substrates. We have developed a Generalized Electrochemical Aggregative Growth Mechanism which mimics the atomistic processes during the early stages of thin-film growth, by incorporating nanoclusters as building blocks. We discuss the influence of new processes such as nanocluster self-limiting growth, surface diffusion, aggregation, and coalescence on the growth mechanism and morphology of the resulting nanostructures. Self-limiting growth mechanisms hinder nanocluster growth and favor coalescence driven growth. The size of the primary nanoclusters is independent of the applied potential and deposition time. The balance between nucleation, nanocluster surface diffusion, and coalescence depends on the material and the overpotential, and influences strongly the morphology of the deposits. A small extent of coalescence leads to ultraporous dendritic structures, large surface coverage, and small particle size. Contrarily, full recrystallization leads to larger hemispherical monocrystalline islands and smaller particle density. The mechanism we propose represents a scientific breakthrough from the fundamental point of view and indicates that achieving the right balance between nucleation, self-limiting growth, cluster surface diffusion, and coalescence is essential and opens new, exciting possibilities to build up enhanced supported nanostructures using nanoclusters as building blocks.

Potentiostatic electrodeposition of Pt on GC and on HOPG at low loadings: Analysis of the deposition transients and the structure of Pt deposits

“…1a) the nucleation maximum is preceded by a pronounced current decay at low deposition times. Similar decaying current transients at deposition times exceeding those characteristic of the double layer charging, have also been reported in the literature [20,33,34]. Analysis of the deposition transients for Pt (IV) in logarithmic coordinates (Fig.…”

“…Recently, Ustarroz proposed the so-called "generalized electrochemical aggregative growth mechanism" [33], comprising nucleation of metal clusters, their growth to a critical (limited by adsorption) size, followed by their surface diffusion, aggregation, coalescence, and recrystallization. Since, diffusion on the support surface must depend on its type and topography, the similarity of the deposition transients on the GC and HOPG supports in this We assume that secondary crystals nucleate at the surface of Pt particles, whose primary growth beyond a certain size is hindered by adsorption of either chloride ions (in this work at potentials E d > 0.060 V vs. RHE), or hydrogen adatoms (E d < 0.060 V vs. RHE when the H UPD coverage is high).…”

Nucleation and Aggregative Growth of Palladium Nanoparticles on Carbon Electrodes: Experiment and Kinetic Model

“…30 Such features are abundant on the ZYB grade HOPG used, but absent from the TEM grid, which may explain the slower kinetics that are evident when the TEM grid is used as the electrode. The TEM images acquired in this study suggest that an aggregative mechanism operates in the electrochemical nucleation and growth of metal NPs, 13,27,28 wherein NPs form and aggregate into larger nanostructures. Assuming that all nanostructures are generated from NPs, which is reasonable based on the TEM images, and that all NPs have spherical shapes, N0 can also be estimated from the total charge of the reduction current-time curves according to equation (1):…”

Magnetic fields in electrochemistry: The Lorentz force. A mini-review

“…[33,36] Electrodeposition performed on TEM grids by Ustarroz et al has shown that the nucleation sites originate from the assembly of tiny mobile subnuclei. [37] Therefore, the fact that experiments performed in magnetic fields produce a larger number of particles would imply that the early nuclei are somehow stabilized by the field, with growth setting in before they are able to assemble. The physical basis of this magnetic influence on nucleation is not clear, although the subsequent growth may be influenced by micro-MHD, as suggested by Aogaki.…”