New Insights into Fundamental Electron Transfer from Single Nanoparticle Voltammetry.

The reductive redox behavior of oxygen in aqueous acid solution leading first to adsorbed superoxide species at single palladium coated multiwalled carbon nanotubes (of length ca. 5 μm and width 130 nm) is reported. The small dimensions of the electroactive surface create conditions of high mass-transport permitting the resolution of electrode kinetic effects. In combination with new theoretical models, it is shown that the physical location of the formed product within the double layer of the electrode profoundly influences the observed electron transfer kinetics. This generically important result gives new physical insights into the modeling of the many electrochemical processes involving adsorbed intermediates.