Study of spillover effects with the rotating disk electrode

Abstract

An analysis is presented of spillover effects on electrochemical reactions taking place at catalyst centres, by using the rotating disk electrode technique. The equations are derived for the current response of a dispersion of catalyst centres supported on a rotating disk by assuming two parallel contributions: one limited by the convective–diffusive transport, and the other by spillover. The spillover contribution arises as a result of the adsorption of active species on the support and surface diffusion towards the catalyst centres. It is assumed that the dissolved concentration of species on the rotating disk surface is homogeneous, which is shown to be better accomplished at high enough rotation rates and small catalyst centres. The Levich equation for a continuous disk electrode appears as a limiting case at high coverages or high spillover. A factor ( B sp /2 zF), with well defined physical meaning, can be obtained from rotating disk experiments to characterise quantitatively the influence of the spillover effect on the electrochemical reaction. Examples of application to real systems are shown, including hydrogen oxidation reaction and oxygen reduction over platinum nanoparticles and molecular catalyst centres. It is shown that the rotating disk technique can be used to obtain quantitative information of spillover effects on electrochemical reactions.