Area determination in fractal surfaces of Pt and Pt---Ru electrodes

Abstract

A fractal approach using corrugation data to calculate surface area is offered as an alternative to gas adsorption technique. The surfaces of mechanically polished polycrystals of pure Pt and Pt---Ru(40%) alloy were examined using scanning tunneling microscopy. Over a range of 0.01–10 μm lengths, three fractal dimensions were identified. Measurements made at randomly selected locations separated by distances >0.1 mm showed the existence of the three domains everywhere. However, in each domain, the fractal dimensions, D, varied from one location to another, suggesting a stochastic distribution of D. The stochastic data was used to calculate the surface area. In the pure Pt case, the area calculated on this basis correlated well with the area measured by the anodic stripping of adsorbed hydrogen. The usefulness of the fractal approach to area calculation in the Pt---Ru alloy, where the hydrogen absorption technique cannot be used, is demonstrated.