Electrochemical quartz-crystal microbalance study of silver and copper electrodeposition on bare and iodine-covered platinum electrodes

https://doi.org/10.1016/j.jelechem.2004.02.014Get rights and content

Abstract

Electrodeposition of silver and copper on iodine-covered and bare polycrystalline Pt electrodes is studied with the electrochemical quartz-crystal microbalance (EQCM). Voltammetry of silver on the iodine-covered surface shows single deposition and stripping peaks, with masses appropriate for silver. This is an ideal calibration system, because similar interactions are present between the electrolyte and the iodine atoms in the presence and absence of silver. This system was used as a reference point to interpret the deviations from ideal mass that occur in the absence of iodine. In the absence of iodine, four distinct deposition and stripping regions are observed. A lower mass than the ideal silver mass for multilayer silver electrodeposition was attributed to smoothening of the electrode. A comparative study of the analogous copper system is also reported.

Introduction

The electrochemical quartz-crystal microbalance (EQCM) has made a significant impact in recent years as an in situ technique capable of measuring the mass increase or decrease at the electrode surface as a function of potential [1], [2]. The mass response should ideally be due only to the surface reactions; however studies have been made on the effects of solution viscosity and temperature [3], electrode orientation [4], solvent molecules at the interface [5], [6], [7], [8], mass location on the electrode [9] and surface morphology/roughness [10], [11]. Metal deposition systems have been popular targets of EQCM study, including both underpotential and overpotential deposition [12], [13], [14] with a wide variety of substrates, metals and electrolytes. These apparently simple systems can give masses that deviate from those expected based on the stoichiometry of the known deposition reaction. These deviations call into question the utility of the EQCM if they are due to effects such as those above, but if they are not due to such artifacts then they may be a source of useful information on the deposition process itself. It is important therefore to find some systems or conditions, under which artifacts are absent, to use as reference points. Here, we address these issues for silver and copper electrodeposition on iodine-covered and bare Pt electrodes.

In the case of silver electrodeposition, Vatankhah et al. [15] have recently undertaken a careful study of the conditions under which silver deposition can be used as a calibration system. They showed that reliable and consistent results can be obtained from chronopotentiometry, chronoamperometry, and cyclic voltammetry (CV) measurements extrapolated to zero sweep rate, but that deviations occur in CV measurements at higher sweep rates, e.g., 20 mV s−1. Thicker films (7–15 monolayers (ML)) were required for reliable calibration. Since their objective was to find a reliable calibration procedure, they did not investigate in detail the reasons for deviations at higher sweep rates, other than to suggest that diffusion may be playing a role. Here, we show that if the deposition occurs instead on an iodine-covered surface, deviations from the ideal mass do not occur at the same sweep rates. This result means that the deposition of silver on iodine-covered Pt may be a good system for calibrating the EQCM. It also means that the deviations from ideal mass in the absence of iodine have an origin in the growth mode of the film itself, since the effects of artifacts would be similar in the two systems. We suggest that the ideal mass for deposition in the presence of iodine is due to a consistent interaction of the iodine with the electrolyte in the presence or absence of silver, and to a layer-by-layer growth mode (constant roughness) for thicker films. In contrast, a reduction in roughness occurs as silver is deposited in the absence of iodine, which leads to a deviation from the ideal mass.

The deposition of silver on the iodine-covered surface was chosen as a comparative system because the silver is known to deposit underneath the iodine layer in the archetypal system: Ag deposition onto Pt(1 1 1)(7×7)R19.1°–I to give the “silver iodide” surface compound Pt(1 1 1)(3 × 3)AgI. This system was first discovered by Hubbard et al. [16], [17], and has since been well investigated by others ([18] and refs. therein). Available evidence suggests that introducing steps [19], changing the close-packed iodine layer to (3 × 3) [20], or changing the crystal face to Pt(1 0 0) [21] does not alter the fact that the silver deposits underneath the iodine, so that we expect this also to be true for deposition on the polycrystalline electrodes used here. The iodine layer before and after deposition should be a nearly close-packed layer exposed to the solution, so that the interactions with the electrolyte may be expected to be similar. Furthermore, the iodine layer on Pt acts as a van der Waals surface that may be used as a substrate for non-dissociative adsorption of large organic molecules [22]. In the present case, the interactions with the electrolyte are expected to be weak and non-directional.

Similar studies have been carried out for copper deposition onto iodine-covered electrodes [23], [24], [25], [26]. On single crystal surfaces, LEED indicates that the CuI structures are well ordered [23], but scanning tunneling microscopy studies performed by Baltruschat et al. [27] revealed the formation of three-dimensional islands of copper as the deposition proceeded.

Section snippets

Experimental

EQCM experiments were carried out using a glass electrochemical cell fitted with a TeflonTM quartz crystal holder similar to the design of Jerkiewicz et al. [4]. The 9-MHz crystals were purchased from Princeton Applied Research and had platinum pads (0.5 cm diameter, geometric area=0.196 cm2) deposited onto a thin titanium layer on unpolished quartz substrates. A phase-locked oscillator (Maxtek PLO-10i) drove the oscillation of the crystal. Shifts in the resonant frequency of the crystal were

Silver electrodeposition onto iodine-covered polycrystalline platinum

The current and frequency responses as a function of potential for the system with and without silver present are shown in Fig. 2. It is evident that in the absence of silver, both the current and frequency responses are small over the 0.4–1.0 V potential range, indicating little or no change in the iodine layer. There is a 5-Hz change in frequency over this potential range. This reproducible change is small compared to the changes for the silver reactions discussed below, and will be discussed

Discussion

The electrodeposition of silver on iodine-covered Pt gives a frequency change that agrees with the prediction of the Sauerbrey equation within the measurement error. It can therefore be used as a calibration system for a Pt-covered quartz crystal. The ideal mass for silver is measured over a large coverage range, from a fraction of a monolayer to more than 11 monolayers. We attribute this ideal behavior to the fact that the deposition gives a smooth deposit with the iodine layer constantly

Conclusions

Metal electrodeposition of metal cations is significantly affected by interactions between the surface and the solution brought about by changes in surface roughness accompanying the film deposition. This has been demonstrated through a comparison of silver and copper deposition onto both bare and iodine-coated electrodes. In the case of silver, the cyclic voltammogram of the coated electrode in supporting electrolyte is very simple, showing one deposition and one stripping process in the

Acknowledgements

We thank the Natural Sciences and Engineering Research Council of Canada and the University of Victoria for financial support of this research. C.J. also thanks these institutions for the award of postgraduate scholarships. We thank Dr. Gregory Jerkiewicz for useful discussions.

References (40)

  • S. Bruckenstein et al.

    Electrochim. Acta

    (1985)
  • G. Jerkiewicz et al.

    Electrochem. Commun.

    (1999)
  • G. Zilberman et al.

    Electrochim. Acta

    (2000)
  • V. Daujotis et al.

    J. Electroanal. Chem.

    (1998)
  • M.C. Santos et al.

    Electrochem. Commun.

    (2000)
  • M.R. Deakin et al.

    J. Electroanal. Chem.

    (1988)
  • A. Bund et al.

    Electrochim. Acta

    (2000)
  • G. Vatankhah et al.

    Electrochim. Acta

    (2003)
  • A.T Hubbard et al.

    J. Electroanal. Chem.

    (1983)
  • J.L. Stickney et al.

    Surf. Sci.

    (1983)
  • M. Labayen et al.

    Surf. Sci.

    (2001)
  • T. Solomun et al.

    J. Electroanal. Chem.

    (1984)
  • M. Labayen et al.

    J. Electroanal. Chem.

    (2000)
  • M. Labayen et al.

    J. Electroanal. Chem.

    (2000)
  • J.H. White et al.

    J. Electroanal. Chem.

    (1989)
  • G.M. Bommarito et al.

    J. Electroanal. Chem.

    (1994)
  • V.I. Birss et al.

    J. Electroanal. Chem.

    (1993)
  • R. Schumacher et al.

    Surf. Sci.

    (1985)
  • P.A. Thiel et al.

    Surf. Sci. Rep.

    (1987)
  • K. Shimazu et al.

    J. Electroanal. Chem.

    (1992)
  • Cited by (11)

    • Adsorption of gelatin during electrodeposition of copper and tin-copper alloys from acid sulfate electrolyte

      2014, Surface and Coatings Technology
      Citation Excerpt :

      Therefore, mechanisms for gelatin–surface interactions during copper and copper–tin electrodeposition were studied by electrochemical techniques of cyclic voltammetry and chronoamperometry in static conditions. The present work also describes the analyses of the electrochemical quartz microbalance (EQCM) technique [43,44], supplying sensitive data on mass changes associated with the deposition process and the different interactions with additives. The morphology and structure of copper and copper–tin deposits, obtained by chronoamperometry, are investigated by scanning electron microscopy (SEM), polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS), and X-ray photon electron spectroscopy (XPS).

    View all citing articles on Scopus
    View full text