Electrocatalysis under Conditions of High Mass Transport Rate: Oxygen Reduction on Single Submicrometer-Sized Pt Particles Supported on Carbon

The effect of the mass transport coefficient of reactant and product species during the oxygen reduction reaction, orr, on platinum in an acidic electrolyte has been experimentally examined and kinetically modeled. By using carbon electrodes having electroactive radii on the nanometer scale it is possible to produce single Pt particles having effective radii ranging from several micrometers to several tens of nanometers. As the mass transport coefficient is directly related to the size of these platinum particles, it is possible to examine the effect of mass transport on the orr in regions inaccessible to other experimental techniques. At the smallest of these Pt particles, mass transport coefficients equivalent to a rotating disk electrode at rotation rates (ω) of greater than 108 rpm are obtainable. Under low mass transport conditions equivalent to those obtainable using the normal rotating disk technique (i.e, ω < 10 000 rpm), oxygen reduction is seen to proceed via a four-electron reduction to water a...