Electrochemical Deposition and Reoxidation of Au at Highly Oriented Pyrolytic Graphite. Stabilization of Au Nanoparticles on the Upper Plane of Step Edges

• Published in: The journal of physical chemistry. B 2003-01, Vol.107 (2), p.451-458
• Main Authors: Boxley, Chett J, White, Henry S, Lister, Tedd E, Pinhero, Patrick J
• Format: Article
• Language: English
• ISSN: 1520-6106; 1520-5207
• DOI: 10.1021/jp026496j

The electrochemical deposition and reoxidation of Au on the basal plane of highly oriented pyrolytic graphite (HOPG) immersed in a 5 mM AuCl4 -/6 M LiCl solution is reported. Scanning electron microscopy (SEM) and ex-situ atomic force microscopy (AFM) demonstrate that Au nanoparticles, ∼3.3 nm in height and ∼10 nm in diameter, are deposited at times less than ∼1 s. The density of nanoparticles, 6 × 109 cm-2, is of the same order of magnitude as the surface point defect density, suggesting that point defects act as nucleation sites for Au electrodeposition. A small subset of the Au nanoparticles (∼7%) continues to grow between 1 and 50 s, reaching a height of ∼150 nm and a diameter of ∼300 nm. At times greater than 50 s, the larger particles coalesce to yield a surface comprised of a low density (∼2 × 106 cm-2) of micrometer-size Au crystallites surrounded by Au nanoparticles. Double potential step chronocoulometric experiments demonstrate that the electrodeposition of Au is chemically irreversible, a finding supported by SEM and AFM observations of Au nanoparticles and larger crystallites on the surface after long periods of reoxidation (>3600 s). Au nanoparticles are observed to be preferentially deposited on the upper plane of step edges, a consequence of the nonuniform surface electron density that results from relaxation of the graphite lattice near steps.