Nanoparticle Collision Responses Controlled by Surface Adsorption

We present a mechanistic investigation into the collision behavior of individual platinum nanoparticles (Pt NPs) on a carbon ultramicroelectrode (UME) within a hydrazine (N2H4) solution. Our findings demonstrate that the collision response is characterized by a sharp, microsecond-long current spike followed by a steady-state current signal. The data indicate that the initial current spike results from the rapid oxidation of N2H4 molecules pre-adsorbed on the nanoparticle surface. Conversely, the subsequent steady-state current is attributed to the continuous catalytic oxidation of protonated hydrazine (N2H5+), which involves a deprotonation and adsorption step on the platinum surface. As each N2H5+ molecule releases five protons (H+) upon complete oxidation, a significant local pH drop is anticipated around the nanoparticle. This pH change, in turn, constrains the steady-state oxidation current observable from each colliding particle. Our study highlights the crucial role of hydrazine adsorption and local pH variations in the observed collision response of the nanoparticles.