Mesoscopic Transport Effects in Electrocatalytic Reactions

Transport effects may not only influence the rate of electrocatalytic reactions, but also the product distribution. The underlying effects were studied under well-defined reaction and transport conditions, using nanostructured Pt/glassy carbon electrodes, which consist of ordered arrays of electrocatalytically active Pt nanostructures on a planar glassy carbon substrate. The effect of varying the density of the Pt nanostructures or the electrolyte flow rate on the reaction characteristics and product distribution was investigated for appar-ently simple electrocatalytic reactions such as CO oxidation, methanol oxidation and oxygen reduction. It is shown that reduc-ing the Pt coverage leads to an increase of the relative amount of the reaction intermediates. Similar effects are obtained for increas-ing the electrolyte flow rate. The results are discussed on a molecu-lar scale in terms of the ‘desorption − re-adsorption − reaction’ model which we had introduced recently (Y.E. Seidel et al., Fara