Electrochemical Measurement of Hydrogen and Nitrogen Nanobubble Lifetimes at Pt Nanoelectrodes

Abstract

The lifetimes of individual H2 and N2 nanobubbles, electrochemically generated at Pt nanoelectrodes (7–85 nm-radius), have been measured using a fast-scan electrochemical technique. To measure lifetime, a stable single H2 or N2 bubble is first generated by reducing protons or oxidizing hydrazine, respectively, at the Pt nanoelectrode. The electrode potential is then rapidly stepped (<100 μs) to a value where the bubble is unstable and begins to dissolve by gas molecule transfer across the gas/water interface and diffusion. The electrode potential is immediately scanned back to values where the bubble was initially stable. Depending on the rate of this second voltammetric scan, the initial bubble may or may not have time to dissolve, as is readily determined by the characteristic voltammetric signature corresponding to the nucleation of a new bubble. The transition between these regimes is used to determine the bubble's lifetime. The results indicate that dissolution of a H2 or N2 nanobubble is, in part, limited by the transfer of molecules across the gas/water interface. A theoretical expression describing mixed diffusion/kinetic control is presented and fit to the experimental data to obtain an interfacial gas transfer rate of ∼10−9 mol N−1 s−1.