Nucleation at liquid∣liquid interfaces: electrodeposition without electrodes

Abstract

A model has been developed for diffusion controlled electrodeposition of metallic particles at the interface between two immiscible electrolyte solutions. A rate law was derived for the case where no preferential nucleation sites are present. Palladium particles were deposited at the water 1,2-dichloroethane interface by reduction of aqueous ammonium palladate using butylferrocene in the organic phase as electron donor. Experimental results were in good agreement with the theoretical model derived. The potential dependence of the nucleation rate was found to follow a classical exponential law.

In situ XAFS Study of Palladium Electrodeposition at the Liquid/Liquid Interface

“…As discussed by Schiffrin and co-workers, the reaction is diffusion limited not only by the metal precursor in the aqueous phase but also by the organic reducing agent [28]. As nanoparticles begin to nucleate at the interface there are two factors driving the preferential forward reaction: first, the formation of a lower energy interface e.g.…”

“…Second, there is the increased likelihood of reactant interaction -initially the reactants must come in to direct contact at the interface for the electron transfer process to occur, but as the particle begins to grow there is an increased reaction cross-section, as further electron transfer processes can occur between reactants present anywhere on the surface. Therefore the particles can be considered as miniature solid bipolar electrodes adsorbed at the interface [28]. Whilst these two processes contribute to the driving force for the forward reaction, the rate may become restricted by the formation of a reactant depletion zone around the newly formed metal structure, which leads to either diffusion limited growth or the dissolution of unstable clusters.…”

“…The electrochemical deposition of Pd at the liquid/liquid interface is reliant on the application of potential in order to drive the heterogeneous electron transfer process between Pd 2+ (aq) and Fc (org) (Figure 2) [28,41]. [51], however the actual potential is also a function of the chloride ion concentration [52].…”

“…on a "conventional" electrode surface, in the sense that an electron transfer process results in the formation of a zero valent nucleus, which must rapidly grow to a certain size to become stable. The electrodeposition of a number of metals at the liquid/liquid interface has been reported in the literature including Au, Ag, Pt and Pd [21][22][23][24][25][26][27][28], as reviewed elsewhere [29]. In the case of Au nucleation it has been shown that the lack of defect sites can completely inhibit the nucleation process under certain conditions [30].…”

Modifying the liquid/liquid interface: pores, particles and deposition

“…11 The solution phase synthetic strategies are, in the main, empirical with a lack of quantitative data on how such particles are assembled-which hampers understanding of how their growth may be controlled. My research group-and others-have been developing an approach to this problem, which involves localising the deposition process to interfaces, [12][13][14] specifically to L/L interfaces (see Fig. 2).…”