Pt Nanoelectrodes Sealed in Quartz Capillaries Modified with Underpotential-Deposited Bismuth for Formic Acid Electrooxidation

Platinum disk nano- and micro-electrodes with radii in the range 40 nm-12.5 mu m were fabricated using quartz capillaries and the laser-puller assisted approach. The hydrogen underpotential deposition (H-UPD), performed in a 0.5 M H2SO4 aqueous solution, revealed that the nanoelectrodes, with radii of 160 nm and less, displayed extraordinarily large surface areas, which in terms of roughness factors (RFs, i. e., the ratio of the real surface areas to the geometric surface areas) were in the range 1030-3600. This finding was attributed to diffusion of adsorbed species at the Pt/quartz interface along portions of the Pt wires sealed within the glass. RFs between 2 and 3 were instead found at the microelectrodes. Similar results were also obtained with underpotential-deposited metallic bismuth. In this case, diffusion of Bi adatoms onto the Pt surface was hindered to some extent, providing a RF value of 172. Bi-modified Pt nano- and micro-electrodes were employed to study the electrooxidation of HCOOH, which is of interest in the field of fuel cells. It was found that the nanoelectrode displayed higher activity towards the electrooxidation of HCOOH and tolerance to CO poisoning, compared to the microelectrode.