Spontaneous chemical reactions between hydrogen and oxygen in nanobubbles

TL;DR

This paper reviews the unique behavior of nanobubbles containing hydrogen and oxygen gases generated electrochemically, highlighting their rapid disappearance due to spontaneous combustion reactions in nanoscopic volumes, challenging classical combustion theory.

Contribution

It introduces a surface-assisted mechanism explaining spontaneous reactions in nanobubbles, providing new insights into their rapid combustion and explosive behavior.

Findings

Nanobubbles smaller than 200 nm contain H2 and O2 gases.

These nanobubbles disappear quickly via spontaneous combustion.

A surface-assisted mechanism explains the reactions and explosions.

Abstract

Bulk nanobubbles (NBs) generated electrochemically by short voltage pulses of alternating polarity behave differently from those produced by regular methods. Only bubbles smaller than $200\;$nm are formed in the process and their concentration is very high. Moreover, the bubbles containing both H2 and O2 gases disappear quickly via the combustion reaction, although the reaction in such a small volume cannot happen according to the classical combustion theory. Experimental facts about these unusual NBs are reviewed and current understanding of the observed phenomena is provided. Visualisation methods of a cloud of NBs above the electrodes are briefly discussed. Experimental signatures demonstrating the reaction between the gases in NBs are considered. A surface-assisted mechanism proposed for the combustion reactions in restricted volumes with a high surface-to-volume ratio is discussed. It it explained how the same mechanism may describe the audible explosion of microbubbles, that is observed in certain circumstances.