# Highly energetic phenomena in water electrolysis

## TL;DR

This paper reports on extreme energetic phenomena in water electrolysis within microsystems, where rapid voltage changes produce nanobubbles that can undergo spontaneous combustion, potentially enabling microscopic internal combustion engines.

## Contribution

It reveals the occurrence of spontaneous combustion of nanobubbles in water electrolysis, demonstrating a novel energetic process with potential for microscopic engine development.

## Key findings

- Observation of bubble growth up to 300 um in 50 us
- Detection of mechanical work from bubble combustion
- Identification of spontaneous ignition at room temperature

## Abstract

Water electrolysis performed in microsystems with a fast change of voltage polarity produces optically invisible nanobubbles containing H2 and O2 gases. In this form the gases are able to the reverse reaction of water formation. Here we report extreme phenomena observed in a millimeter-sized open system. Under a frequency of driving pulses above 100 kHz the process is accompanied by clicking sounds repeated every 50 ms or so. Fast video reveals that synchronously with the click a bubble is growing between the electrodes which reaches a size of 300 um in 50 us. Detailed dynamics of the system is monitored by means of a vibrometer by observing a piece of silicon floating above the electrodes. The energy of a single event is estimated as 0.3 uJ and a significant part of this energy is transformed into mechanical work moving the piece. The observations are explained by the combustion of hydrogen and oxygen mixture in the initial bubble with a diameter of about 40 um. Unusual combustion mechanism supporting spontaneous ignition at room temperature is responsible for the process. The observed effect demonstrates a principal possibility to build a microscopic internal combustion engine.