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The nucleation rate of single O2 nanobubbles at Pt nanoelectrodes

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Lohse,  Detlef
Max Planck Institute for Dynamics and Self-Organization, Max Planck Society;

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Citation

Moreno-Soto, A., German, S. R., Ren, H., van der Meer, D., Lohse, D., Edwards, M. A., et al. (2018). The nucleation rate of single O2 nanobubbles at Pt nanoelectrodes. Langmuir, 34(25), 7309-7318. doi:10.1021/acs.langmuir.8b01372.


Cite as: https://hdl.handle.net/21.11116/0000-0001-6D9F-3
Abstract
Nanobubble nucleation is a problem that affects efficiency in electrocatalytic reactions, since those bubbles can block the surface of the catalytic sites. In this article, we focus on the nucleation rate of $\mathrm{O_2}$ nanobubbles resulting from electrooxidation of $\mathrm{H_2O_2}$ at Pt disk nanoelectrodes. Bubbles form almost instantaneously when a critical peak current, $i_\mathrm{nb}^\mathrm{p}$, is applied, but for lower currents, bubble nucleation is a stochastic process in which the nucleation (induction) time, $t_\mathrm{ind}$, dramatically decreases as the applied current approaches $i_\mathrm{nb}^\mathrm{p}$, a consequence of the local supersaturation level, $\zeta$, increasing at high currents. Here, by applying different currents below $i_\mathrm{nb}^\mathrm{p}$, nanobubbles take some time to nucleate and block the surface of the Pt electrode at which the reaction occurs, providing a means to measure the stochastic $t_\mathrm{ind}$. We study in detail the different conditions in which nanobubbles appear, concluding that the electrode surface needs to be pre-conditioned for achieving reproducible results. We also measure the activation energy for bubble nucleation, $E_\mathrm{a}$, which varies in the range from 6 to 30 $kT$, and, assuming a spherical-cap-shaped nanobubble nucleus, we determine the footprint diameter $L=8-15$ nm, the contact angle to the electrode surface $\theta=135-155^\circ$ and the number of $\mathrm{O_2}$ molecules contained in the nucleus (50 to 900 molecules).