Exploring the Mechanisms of Spontaneous Combustion of H_2/O_2 in Nanobubbles Generated by Water Electrolysis

摘要

Previously in our experimental work, a micro-thermal sensor (resistance thermometer) was fabricated to measure the amount of heat produced during the combustion of the H_2/O_2 gases inside the nanobubbles produced by the application of square alternating current (AC) pulses in deionized water and it was observed that the combustion occurred only above a threshold frequency of 15 kHz. Thus in this work, molecular dynamic simulations were conducted to better understand the mechanisms that contribute towards the spontaneous combustion of the H_2/O_2 gases. First, non-reactive simulations were conducted to determine the surface tension of water as a function of the concentration of the dissolved gaseous molecules (O_2), which would in turn help to predict the pressure inside the nanobubbles under supersaturation conditions. Knowing the bubble pressure is a prerequisite for understanding the mechanisms behind the spontaneous combustion of the H_2/O_2 gases. The surface tension of water containing four different supersaturation concentrations (S) of O_2 gas molecules was computed and was found to decrease with an increase in the supersaturation ratio. Next, reactive simulations were conducted based on the first-principles derived reactive force field, ReaxFF. The ignition of the H_2/O_2 gases as a function of the number of initial H radicals available in the system was studied. Without any H radicals, no ignition was detected at 300 K and P = 50 atm but with the addition of H radicals, dissociation of the H_2/O_2 molecules was observed.