Study of the formation and quick growth of thick oxide films using platinum nanoelectrodes as a model electrocatalyst

Recent advances in the development and application of nanoelectrodes

Nanoelectrodes have key advantages compared to electrodes of conventional size and are the tool of choice for numerous applications in both fundamental electrochemistry research and bioelectrochemical analysis. This Minireview summarizes recent advances in the development, characterization, and use of nanoelectrodes in nanoscale electroanalytical chemistry. Methods of nanoelectrode preparation include laser-pulled glass-sealed metal nanoelectrodes, mass-produced nanoelectrodes, carbon nanotube based and carbon-filled nanopipettes, and tunneling nanoelectrodes. Several new topics of their recent application are covered, which include the use of nanoelectrodes for electrochemical imaging at ultrahigh spatial resolution, imaging with nanoelectrodes and nanopipettes, electrochemical analysis of single cells, single enzymes, and single nanoparticles, and the use of nanoelectrodes to understand single nanobubbles.

Mobility and Reactivity of Oxygen Adspecies on Platinum Surface

The adsorption and mobility of oxygen adspecies on platinum (Pt) surface are crucial for the oxidation of surface-absorbed carbon monoxide (CO), which causes the deactivation of Pt catalyst in fuel cells. By employing nanoelectrode and ultramicroelectrode techniques, we have observed the surface mobility of oxygen adspecies produced by the dissociative adsorption of H2O and the surface reaction between the oxygen adspecies and the preadsorbed CO on the Pt surface. The desorption charge of oxygen adspecies on a Pt nanoelectrode has been found to be in proportion to the reciprocal of the square root of scan rate. Using this information, the apparent surface diffusion coefficient of oxygen adspecies has been determined to be (5.61 ± 0.84) × 10(-10) cm(2)/s at 25 °C. During the surface oxidation of CO, two current peaks are observed, which are attributed to CO oxidation at the Pt/electrolyte interface and the surface mobility of the oxygen adspecies on the adjacent Pt surface, respectively. These results demonstrate that the surface mobility of oxygen adspecies plays an important role in the antipoisoning and reactivation of Pt catalyst.

Electrochemical Generation of a Hydrogen Bubble at a Recessed Platinum Nanopore Electrode

We report the electrochemical generation of a single hydrogen bubble within the cavity of a recessed Pt nanopore electrode. The recessed Pt electrode is a conical pore in glass that contains a micrometer-scale Pt disk (1-10 μm radius) at the nanopore base and a nanometer-scale orifice (10-100 nm radius) that restricts diffusion of electroactive molecules and dissolved gas between the nanopore cavity and bulk solution. The formation of a H2 bubble at the Pt disk electrode in voltammetric experiments results from the reduction of H(+) in a 0.25 M H2SO4 solution; the liquid-to-gas phase transformation is indicated in the voltammetric response by a precipitous decrease in the cathodic current due to rapid bubble nucleation and growth within the nanopore cavity. Finite element simulations of the concentration distribution of dissolved H2 within the nanopore cavity, as a function of the H(+) reduction current, indicate that H2 bubble nucleation at the recessed Pt electrode surface occurs at a critical supersaturation concentration of ∼0.22 M, in agreement with the value previously obtained at (nonrecessed) Pt disk electrodes (∼0.25 M). Because the nanopore orifice limits the diffusion of H2 out of the nanopore cavity, an anodic peak corresponding to the oxidation of gaseous and dissolved H2 trapped in the recessed cavity is readily observed on the reverse voltammetric scan. Integration of the charge associated with the H2 oxidation peak is found to approach that of the H(+) reduction peak at high scan rates, confirming the assignment of the anodic peak to H2 oxidation. Preliminary results for the electrochemical generation of O2 bubbles from water oxidation at a recessed nanopore electrode are consistent with the electrogeneration of H2 bubbles.