Deciphering Redox Pathways in Aqueous Microdroplets: Simultaneous Production of Hydrogen Peroxide, Hydrogen, and Organics from Ethyl Palmitate as Renewable Feedstock

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Abstract Ultrasonication of biphasic mixtures involving water and oil forms water microdroplets, offering a promising platform that spontaneously generates hydrogen peroxide and hydrogen gas. However, the redox mechanisms underpinning these transformations are poorly understood, and most existing studies rely heavily on petroleum-derived alkanes like hexadecane. Herein, we introduce a sustainable alternative by utilizing ethyl palmitate, a renewable and plant-based oil as the organic phase. We move beyond the reactive microdroplet narrative to provide a mechanistic framework that captures redox transformations in sonicated emulsive water microdroplets (SEWMs). We demonstrate the catalyst-free production of hydrogen peroxide (∼12 mM) and hydrogen gas (∼0.75 μmol) via reduction and simultaneous oxidation of ethyl palmitate into value-added organic products (generating millimolar amounts of methanol, ethanol, methanediol, oxydimethanol, formic acid, and acetic acid), thus completing a redox coupled process within the microdroplet environment. Bright-field microscopy imaging analyses reveal that increased droplet populations and decreased droplet size correlate with higher reactivity. Furthermore, H2O2 and H2 formation exhibits anticorrelated trends, indicating competing interfacial reaction pathways and tunable product selectivity by varying the gaseous environment during ultrasonication. Together, these findings expand microdroplet chemistry to plant-based oil systems and highlight SEWMs as a renewable platform for sustainable redox chemical transformations.

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