Observation of spontaneous combustion of hydrogen and oxygen in microbubbles

Experimental evidence is presented that combustion can ignite at room temperature spontaneously inside microbubbles filled with mixture of hydrogen and oxygen. We perform water electrolysis in a closed microchamber by voltage pulses of alternating polarity at repetition frequencies $≥100 kHz$ to pump the gases rapidly into the electrolyte and produce extreme supersaturation with both gases. After a delay of $300−600 μs$⁠, we observe stroboscopically microbubbles of $5−20 μm$ in diameter that appear in between the electrodes for several microseconds. Each event is accompanied by a pressure jump of $0.1−1 bar$ that is measured interferometrically. The pressure jumps are attributed to combustion of the gases in the microbubbles.