Sensitivity of Electrochemical Adlayer Structure to the Metal Crystallographic Orientation: Potential-Dependent Iodide Adsorption on Au(100) in Comparison with Other Low-Index Surfaces

Abstract

The potential-dependent ordered atomic structures formed for iodide adsorption on Au(100) from dilute aqueous alkali iodide electrolytes as discerned by means of in-situ scanning tunneling microscopy (STM) are reported and compared to the corresponding behavior of the other two low-index faces, Au(111) and (110) . As in related studies, emphasis is placed on linking the microscopic structural information to the voltammetric and other macroscopic electrochemical response, including the use of 'potentiodynamic' STM tactics where real-space images are acquired during appropriate electrode potential steps or sweeps. While relatively low iodide coverages, theta sub I approx. 0.1, are sufficient to lift the hexagonal Au(100) reconstruction, yielding large ordered (1 x 1) domains by ca-0.6 V vs SCE, ordered iodide adlayers are formed only above -0.2 V. A compressible incommensurate (2 sq rt 2 x p sq rt 2) phase (theta sub I, approx. 0.46 - 0.49) is observed between ca -0.2 and 0 V, which reverts to a distinct (2 sq rt of 2 x sq rt of 2)R45 deg structure (theta sub I approx. 0. 5) featuring uniform binding in twofold bridging sites. Interestingly, while the latter structure is retained locally at higher potentials, it is interspersed with narrow (3-4 atom wide) strips having a rotated hexagonal pattern. The latter becomes increasingly dense, and eventually dominant, towards higher potentials. This microscopically nonuniform (or spatially modulated ) phase is noteworthy as well as unusual; the corresponding iodine phases on Au(111) and (110) display, as is common, structural uniformity at a given potential.

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Document Details

Document Type
Technical Report
Publication Date
Feb 01, 1994
Accession Number
ADA276714

Entities

People

  • Fan-chen Liu
  • Gregory J. Edens
  • Michael J. Weaver
  • Xiaoping Gao

Organizations

  • Purdue University

Tags

Communities of Interest

  • Energy and Power Technologies
  • Materials and Manufacturing Processes

DTIC Thesaurus Topics

  • Acquisition
  • Adsorption
  • Capacitance
  • Chemistry
  • Crystal Structure
  • Data Acquisition
  • Electrochemistry
  • Electrodes
  • Geometry
  • Measurement
  • Packing Density
  • Periodic Variations
  • Phase
  • Phase Transformations
  • Physical Chemistry
  • Transitions
  • Two Dimensional

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  • Electrochemical Surface Science
  • Materials Science and Engineering.

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  • Space