Issue 9, 2024

Busting the myth of spontaneous formation of H2O2 at the air–water interface: contributions of the liquid–solid interface and dissolved oxygen exposed

Abstract

Recent reports on the spontaneous formation of hydrogen peroxide (H2O2) at the air–water and solid–water interfaces challenge our current understanding of aquatic chemistry and have ramifications on atmosphere chemistry models, surface science, and green chemistry. Suggested mechanisms underlying this chemical transformation include ultrahigh instantaneous electric fields at the air–water interface and the oxidation of water and reduction of the solid at the solid–water interface. Here, we revisit this curious problem with NMR spectroscopy (with an H2O2 detection limit ≥50 nM) and pay special attention to the effects of nebulizing gas, dissolved oxygen content, and the solid–water interface on this chemical transformation in condensed and sprayed water microdroplets. Experiments reveal that the reduction of dissolved oxygen at the solid–water interface predominantly contributes to the H2O2 formation (not the oxidation of hydroxyl ions at the air–water interface or the oxidation of water at the solid–water interface). We find that the H2O2 formation is accompanied by the consumption (i.e., reduction) of dissolved oxygen and the oxidation of the solid surface, i.e., in the absence of dissolved oxygen, the formation of H2O2(aq) is not observed within the detection limit of ≥50 nM. Remarkably, the tendency of the solids investigated in this work towards forming H2O2 in water followed the same order as their positions in the classic Galvanic series. These findings bust the prevailing myths surrounding H2O2 formation due to the air–water interface, the ultrahigh electric fields therein, or the micro-scale of droplets. The hitherto unrealized role of the oxidation of the solid surface due to dissolved oxygen in the formation of H2O2 is exposed. These findings are especially relevant to corrosion science, surface science, and electrochemistry, among others.

Graphical abstract: Busting the myth of spontaneous formation of H2O2 at the air–water interface: contributions of the liquid–solid interface and dissolved oxygen exposed

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Article information

Article type
Edge Article
Submitted
05 dec 2023
Accepted
22 jan 2024
First published
24 jan 2024
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY license

Chem. Sci., 2024,15, 3093-3103

Busting the myth of spontaneous formation of H2O2 at the air–water interface: contributions of the liquid–solid interface and dissolved oxygen exposed

M. A. Eatoo and H. Mishra, Chem. Sci., 2024, 15, 3093 DOI: 10.1039/D3SC06534K

This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. You can use material from this article in other publications without requesting further permissions from the RSC, provided that the correct acknowledgement is given.

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