A simple facet-based method for single crystal electrochemical study

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Abstract

In this paper, we demonstrate a simple facet-based method for single crystal electrochemical study. Based on the design of a simple and proper electrochemical cell using a cone-shaped pipette tip, one of the natural (1 1 1) facets of a Au single crystal bead has been directly used for electrochemical measurements. Since the processes of orientating, cutting and mechanical polishing are avoided, misorientation and mechanical damage to single crystal surface can be eliminated and reliable data are expected. The advantages of the method have been proved by the nice cyclic voltammogram of Ag underpotential deposition (UPD), a system that has shown large discrepancy in cyclic voltammograms reported by different laboratories due to the dissimilarity of the surface state. The sharp and reversible UPD peaks from the facet-based measurements resemble the best of the reported data in the literature. The method can be extended to (1 1 1) surfaces of some other metals.

Introduction

The progress in single crystal electrochemistry has benefited from the technique of preparing well-defined Pt single crystal electrode invented by Clavilier et al. [1]. In this technique, one end of a Pt wire is melted in hydrogen–oxygen flame to form a single crystal bead of about 3 mm diameter, exposing eight natural (1 1 1) facets in octahedral configuration and several smaller (1 0 0) facets. The single crystal bead is then cut at a specific orientation followed by mechanical polishing and temperature or flame annealing to obtain a sufficiently large and smooth single crystal surface for electrochemical measurement via hanging meniscus. Following the same procedure, other noble metals such as Au, Ir, Rh and Pd can also be prepared [2]. This method has enabled electrochemists to prepare clean and well-defined single crystal electrodes in their own laboratories in an economical and practical way, and thus promoted substantially the development of single-crystal electrochemistry. Direct use of one of the natural facets of the single crystal bead has also provided an essential basis for many in situ STM measurements [3], the width of the terraces is from several hundred nanometers to around 1 μm.

However, the above method of preparing single crystal surface for electrochemical measurement involves several steps. Considerably long time is usually spent to prepare one electrode, and much experience is needed. Even though, misorientation and scratches introduced in the process of cutting and polishing is unavoidable like commercial massive single crystal electrodes. Especially when the researchers do not have enough experience, the quality of single crystal electrode cannot be guaranteed. For example, diversities of cyclic voltammograms for the UPD of Ag on Au(1 1 1), which cannot be negligible, were reported in the literature [4]. Therefore, more easily handled methods are highly desirable for more precise single crystal electrochemical measurements.

As has been mentioned earlier, the carefully prepared single crystal beads have eight (1 1 1) facets in an octahedral configuration and several (1 0 0) facets. If these facets can be directly used for electrochemical measurements like for in situ STM measurements, the processes of orientating, cutting and polishing are not needed. Thus not only can time be saved in a great deal, but also the problem of misorientation and mechanical damage can be avoided. However, with conventional electrochemical cells, electrochemical measurements cannot be conducted on such a small natural facet because electrolyte will also contact the other parts of the bead surface near the facet. Therefore a properly designed cell configuration for electrochemical measurements on single crystal facets becomes the key of this approach.

Here we present a simple experimental setup to carry out electrochemical measurements on single crystal facets. We mention that though a similar approach has been conducted on Pt beads and good results from the (1 1 1) facet and the (1 1 0) and (1 0 0) regions were obtained which agreed well with those on the larger cut faces of these orientations of a crystal [5], no experimental details were given. The cyclic voltammogram of the oxidation behavior of Au(1 1 1) surface is performed to check the quality of the electrode and calculate the actual surface area. Ag underpotential deposition on Au(1 1 1) is then reinvestigated, which had been characterized by a certain degree of irreproducibility from different laboratories [4]. The results from cyclic voltammograms are compared with those in literature and prove that the method works well for single crystal electrochemical studies.

Section snippets

Experimental

The experimental setup for electrochemical measurement using the facet of a single crystal bead is shown in Fig. 1a. The single crystal bead prepared using Clavilier’s method is about 3 mm in diameter. The bead was fixed on an Au foil with one of the (1 1 1) facets facing upwards and serving as the working electrode. A pipette tip was used as the electrochemical cell, which was a standard polypropylene pipette tip for use with pipettor. The pipette tip was purchased from Shanghai Sangon Biological

The electrochemical behavior of Au(1 1 1) facet

The electrochemical behavior of Au(1 1 1) in aqueous sulfuric acid solution have been extensively investigated [6], [7], [8]. At the potential region of oxide formation, single crystal electrodes of different index show characteristic peaks corresponding specifically to the orientation of the single crystal surface, which serve as the fingerprints for judging the orientations as well as the quality of the single crystal electrodes. Here the cyclic voltammogram of the oxidation process is used to

Conclusions

We have demonstrated a single crystal bead’s facet-based method, which is simple, yet accurate for single crystal electrochemical study. Reliable data from perfect Au(1 1 1) surfaces have been obtained, clarifying the conclusions drawn from previously reported literature. This method can be extended to (1 1 1) surfaces of some other noble metals. In addition to more sufficient oxygen removal, the experimental setup can be improved further, for example, the position and the type of the reference

Acknowledgements

This work was supported by the Natural Science Foundation of China (NSFC Nos. 20273056, 20303013, 20433040) and the Special Funds for Major State Basic Research Project of China (“973” Project No. 2002CB211804).

References (15)

  • J. Clavilier et al.

    J. Electroanal. Chem.

    (1980)
  • K. Itaya

    Prog. Surf. Sci.

    (1998)
  • V. Rooryck et al.

    J. Electroanal. Chem.

    (2000)
  • H. Angerstein-Kozlowska et al.

    J. Electroanal. Chem.

    (1987)
  • A. Hamelin

    J. Electroanal. Chem.

    (1996)
  • M.A. Schneeweiss et al.

    Solid State Ionics

    (1997)
  • B.E. Conway

    Prog. Surf. Sci.

    (1995)
There are more references available in the full text version of this article.
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