Electrocatalytic Reduction of Oxygen at Single Platinum Nanowires

Abstract

Here we report the preparation and electrochemical characterization of single Pt nanowire electrodes with radii ranging from 25 to 130 nm for their electrocatalytic activity toward the oxygen reduction reaction (ORR). Ultralong Pt nanowires were prepared by a laser pulling process. Single Pt nanowire electrodes were fabricated by metal deposition and lithography patterning to expose just a small portion (10–20 μm in length) of the nanowire for electrocatalytic studies. These wires were characterized thoroughly using cyclic voltammetry, under potential deposition of copper, and scanning electron microscopy. We have shown that their electrocatalytic activity toward ORR slightly decreases as the nanowire radius is reduced as measured by the onset potential. Additionally, the current density for the ORR decreases and the mass activity increases as the wire becomes smaller. The faradaic current was modeled on single nanowire electrodes, and the current was found to match the experimental value with outer-sphere redox species. However, significant variance was shown between the modeled ORR current and the measured value. The deviation of the ORR current on the wires is likely due to the presence of F– ions on Pt and the increased adsorption energy of oxygenated species, thus leading to a hindering of the reaction kinetics of the catalytic process. This is confirmed by Tafel plots where the slope is seen to change at a lower potential as compared to bulk polycrystalline Pt.