Sprayed\nOil–Water Microdroplets as a Hydrogen\nSource

Abstract

Liquid\nwater provides the largest hydrogen reservoir on the earth’s\nsurface. Direct utilization of water as a source of hydrogen atoms\nand molecules is fundamental to the evolution of the ecosystem and\nindustry. However, liquid water is an unfavorable electron donor for\nforming these hydrogen species owing to its redox inertness. We report\noil-mediated electron extraction from water microdroplets, which is\neasily achieved by ultrasonically spraying an oil–water emulsion.\nBased on charge measurement and electron paramagnetic resonance spectroscopy,\ncontact electrification between oil and a water microdroplet is demonstrated\nto be the origin of electron extraction from water molecules. This\ncontact electrification results in enhanced charge separation and\nsubsequent mutual neutralization, which enables a ∼13-fold\nincrease of charge carriers in comparison with an ultrapure water\nspray, leading to a ∼16-fold increase of spray-sourced hydrogen\nthat can hydrogenate CO₂ to selectively produce CO. These\nfindings emphasize the potential of charge separation enabled by spraying\nan emulsion of liquid water and a hydrophobic liquid in driving hydrogenation\nreactions.