Real surface area measurements in electrochemistry

A scanning tunnelling microscope can image surfaces down to the atomic scale. Its very high resolution is caused by its local probing mechanism: a tunnel current which flows through the outermost atom of a scanning tip to the sample. Its invention, about ten years ago, was based on an ingenious blend of quantum physics, mechanical design and electronic control. Since then, it has proved to be a very versatile instrument. Its applications range from the characterization of surface roughness to atomic reconstructions, and from doped semiconductors to cell membranes. It can operate in ultra high vacuum, in air, in reactive gases, in corrosive solutions or at cryogenic temperatures. This paper reviews the evolution of scanning tunnelling microscopy in the first decade after its invention. Attention is focused on the basis of STM: tunnelling theory, mechanical design and modes of operation. Representative examples of applications in various fields of research are discussed.

http://idwebhost-202-73.ethz.ch/praktika/analytisch/stm/Rep%20Prog%20phys%2055,%20p1165.pdf

Scanning tunnelling microscopy

Electrochemistry at fractal surfaces

The electrooxidation of CO: a test reaction in electrocatalysis

The investigation of electrocatalytic processes involved in the electrooxidation of organic compounds became a subject of growing interest at the beginning of the 1960s. A tremendous effort was undertaken to develop fuel cells, which theoretically have the ability to directly convert the chemical energy of hydrocarbons into electrical energy without the limitations due to Carnot’s theorem (i.e., with a high energy efficiency), an advantage which is particularly attractive for autonomous power sources.1–3 In such applications the rate of conversion of the organic compound by oxidation into carbon dioxide has to be as high as possible, in order to obtain the maximum energy available from the fuel and thus the maximum efficiency. However, the incomplete oxidation of organic compounds is of great interest as well, if one considers the potential applications for organic electrosynthesis, so that many attempts have been made in this field as well. Rigorous control of the experimental conditions may allow such reactions to become highly selective, leading to the development of industrial processes based on electrochemical reactions for the production of chemicals.4,5

Electrocatalytic Oxidation of Oxygenated Aliphatic Organic Compounds at Noble Metal Electrodes

A direct scanning tunneling microscopy ex-situ determination on the nanometer scale of the topography of electrochemically highly activated platinum electrodes is presented. A correlation between catalytic activity and surface microtopography becomes evident. This result gives support to a structural model for the activated electrode surface. In the model, a volume with a pebble-like structure allows electrocatalytic processes to occur practically free of diffusion relaxation contributions under usual voltammetric conditions.

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Scanning tunneling microscopy of electrochemically activated platinum surfaces. A direct ex-situ determination of the electrode nanotopography

The surface of a number of metals such as platinum, gold, rhodium and palladium, which are of particular interest in catalytic and electrocatalytic processes, either as polycrystalline or single-crystal specimens, can be preferentially orientated by a procedure known as electrochemical faceting1–3. Here we report the first real-space observation in the nanometric range of electrochemically faceted (100)-type Pt electrodes, using scanning tunnelling microscopy (STM)4. Our findings confirm the existence of a faceted surface consisting of flat parts surrounded by ridge-type structures. At the initial stages cluster formation is observed, which subsequently develops in a preferential orientation. This constitutes direct evidence that faceting occurs through a selective electrodissolution/electrodeposition process, which probably involves a fast diffusion of metallic species either in the electrolyte or on the surface.

N. Garcia

Papers

Scanning tunneling microscopy of electrochemically activated platinum surfaces. A direct ex-situ determination of the electrode nanotopography

Surface topography of (100)-type electro-faceted platinum from scanning tunnelling microscopy and electrochemistry

Scanning Tunneling Microscopy of Electrochemically Activated Platinum Surfaces. A Direct Ex-Situ Determination of the Electrode Nanotopography