Bipolar Nanoimpact Transients: Controlling the Redox Potential of Nanoparticles in Solution

In the bulk solution phase the electrical potential of a single metallic nanoparticle can be controlled by its local chemical environment. In this work it is demonstrated how this nanoparticle "redox"potential determines - in the case of platinum - the surface functionality of the nanomaterial. Specifically we report that in the aqueous solution phase the surface adsorption of hydrogen onto the platinum interface is inhibited by the addition of iodine to the solution. The iodine does not competitively inhibit the hydrogen deposition, but rather alters the nanoparticle potential, making it comparatively oxidizing. This work evidences this behavior through single nanoparticle electrochemistry and supports these results with characterization using ex-situ energy dispersive X-ray analysis. We show how the electrochemical response depends on the chemical "redox"state of the nanoparticle in the solution phase; this leads to the first reported example of a bipolar single nanoparticle event characterized by the single nanoparticle impact current transient initially being reductive before switching after ca. 50 ms to being oxidative.