Abstract
Surface disorder and random roughness of electrode surfaces are discussed in terms of Euclidean and fractal models. Roughness development at different metals results from two contributions operating in opposite directions, namely shadowing between growing clusters which leads to rough surfaces, and surface diffusion phenomena which tend to smooth surface irregularities. The second contribution depends on the specific mobility of the deposited metal atoms, the temperature, and the electrolyte composition. Monte Carlo simulations based upon nucleation and growth models show that the growth processes controlled by either surface reactions or mass transport of reacting species, including surface diffusion, produce compact deposits with a weak surface disorder. Conversely, the growth process under mass transport control involving a negligible surface diffusion generates open structures with a strong surface disorder. Rough metal deposits exhibiting a fractal behaviour are considered. The fractal dimension provides a quantitative description of the degree of disorder, the growth mechanism and the reactivity of those surfaces in relation to electrocatalysis.
Highlights
Surface disorder and random roughness of electrode surfaces are discussed in terms of Euclidean and fractal models
Electrocatalytic reactions at solid electrodes involve the participation of adsorbed species acting either as a short half life intermediate or as a poison depending on the electrochemical system
Only in recent years could an explanation of the specific reactivity of the Pt electrode in terms of the metal surface be advanced[2-41 because of the progress made on the structure of solid surfaces, and the possibility of obtaining electrochemical data complemented by in situ surface analysis and scanning tunnelling microscopy (STM) at the atomic level[S] for extremely clean and well-defined single crystal electrochemical systems
Summary
Electrocatalytic reactions at solid electrodes involve the participation of adsorbed species acting either as a short half life intermediate or as a poison depending on the electrochemical system. Only in recent years could an explanation of the specific reactivity of the Pt electrode in terms of the metal surface be advanced[2-41 because of the progress made on the structure of solid surfaces, and the possibility of obtaining electrochemical data complemented by in situ surface analysis and scanning tunnelling microscopy (STM) at the atomic level[S] for extremely clean and well-defined single crystal electrochemical systems. These advances have shortened the gap existing between heterogeneous catalysis and electrocatalysis[6], as they made it possible to know the type and the density of intrinsic and extrinsic defects at solid electrode surfaces, and to follow more precisely the dynamic behaviour of several adsorbates of electrocatalytic interest. This information constitutes part of the basic physicochemical framework for the design of real solid electrode surfaces of interest for electrocatalysis
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