Electrodeposition of Well-Adhered Multifarious Au Particles at a Solid|Toluene|Aqueous Electrolyte Three-Phase Junction Izabela Kaminska, Martin Jonsson-Niedziolka, Agnieszka Kaminska, Marcin Pisarek, Robert Holyst, Marcin Opallo, and Joanna Niedziolka-Jonsson* Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warszawa, Poland ABSTRACT: In order to obtain uniform and reproducible surface enhanced Raman spectroscopy (SERS) platforms, a novel method for deposition of well-adhered multifarious gold particles on a tin-doped indium oxide electrode through electrogeneration at an electrode|gold compound in toluene|aqueous-electrolyte three-phase junction was developed. The electrodeposition was carried out both by double- potential-step chronoamperometry with one pulse for nucleation and one for growth of the particles, and by potentiostatic single-potential- step chronoamperometry. Both procedures give angular, multifarious Au particles with a diameter of 150 ± 40 nm. The size of the particles is independent of deposition time, after an initial growth phase, and controlled by the formation of a microemulsion at the three-phase junction. The particles are likely deposited from the microdroplets and their size is determined by the amount of gold salt in a droplet. The mechanism involves electoreduction of tetraoctylammonium tetrachloroaurate at the tin-doped indium oxide electrode followed by ion transfer across the liquid|liquid interface. The Au particles are strongly adhered to the electrode surface. The Au particle covered electrode enhances Raman scattering on the order of 10 5 -10 6 times for malachite green isothiocyanate. Surface enhanced Raman spectroscopy studies reveal that the reproducibility of the Au particle deposit is excellent both between samples (<15% RSD) and across a single sample (<12% RSD). The obtained nanoparticulate deposit was also demonstrated to show electrocatalytic activity toward dioxygen reduction. ■ INTRODUCTION The electrochemical processes at solid|liquid|liquid interfaces combine specific features of electron transfer at solid|liquid interfaces and ion transfer across liquid|liquid interfaces. 1 Typically a solid|liquid|liquid interface is realized by the deposition of a single or numerous redox active oil droplets on the electrode surface followed by immersion in an aqueous electrolyte. 2 The triple interface is formed at the circumference of the droplet(s). Immersion of a wire or plate electrode into a biphasic system, as shown in Figure 1, with one phase containing electrolyte and the other one containing redox active species, represents a more straightforward method which allows control of the position and the length of the three-phase junction. 3,4 The electrochemical generation of charge in the oil leads to ion transfer across the liquid|liquid interface to balance the excess charge. 3,5,6 If the oil phase initially contains only a neutral electroactive redox probe, the electrochemical reaction starts at the solid|liquid|liquid three-phase junction (purple square in Figure 1), where a large number of ions is available. 3,5,7-10 Although polar solvents, e.g., nitrobenzene, are used as the organic phase in most cases, there are examples of electrochemical redox reactions in nonpolar solvents such as kerosene 11 or toluene 12 followed by ion transfer. Attempts to use the solid|liquid|liquid three-phase junction as a microreactor for electropolymerization of a monomer dissolved in the organic phase have been reported previ- ously. 13-15 A similar arrangement was employed to deposit sol-gel processed hydrophobic silicate stripes 4 or films 16 on a flat surface. The organic phase serves as a source of the hydrophobic precursor while hydrated protons (the catalyst of the sol-gel process) are generated in the aqueous phase. A system consisting of droplets of an aqueous solution of copper salt deposited on an electrode surface immersed in a solution of 1,2-dichloroethane was applied for electrodeposition of metallic structures (copper rings). 14 Recently we have demonstrated the electrodeposition of a Au nanoparticulate stripe at a solid|ionic liquid|aqueous electrolyte interface. 17 Here we will show that metal particles can be deposited on an electrode surface also from a metal salt dissolved in a nonpolar solvent (Figure 1). Received: August 2, 2012 Revised: September 21, 2012 Published: October 2, 2012 Figure 1. Scheme of the electrochemical cell and formation of the Au particle stripe. Article pubs.acs.org/JPCC © 2012 American Chemical Society 22476 dx.doi.org/10.1021/jp307674k | J. Phys. Chem. C 2012, 116, 22476-22485