The Air–Water Interface of Condensed Water Microdroplets does not Produce H2O2

Abstract

Recent reports on the production of hydrogen peroxide (H2O2) on the surface of condensed water microdroplets without the addition of catalysts or additives have sparked significant interest. The underlying mechanism isspeculated to be ultrahigh electric fields at the air-water interface;smaller droplets present higher interfacial area and produce higher (detectable) H2O2 yields. Herein, we present an alternative explanation for these experimental observations. We compare H2O2 production in water microdroplets condensed from vapor produced via (i) heating water to 50–70℃ and (ii) ultrasonic humidification (as exploited in the original report). Water microdroplets condensed after heating do not show any enhancement in the H2O2 level in comparison to the bulk water, regardless of droplet size or the substrate wettability. In contrast, those condensed after ultrasonic humidification produce significantly higher H2O2 quantities. We conclude that the ultrasonication of water contributes to the H2O2 production, not droplet interfacial effects.