HCl Intake via Nanobubbles Induces Redox Radicals for Aqueous Cl 2 and H 2 Production Without Catalyst and Bias Applied

Abstract Bubbling is a widely used method to enhance gas hydration and dissolution in aqueous solutions. Understanding the bubble‐induced interface‐rich aqueous system is crucial for elucidating gas‐involved solution chemical reactions, yet this area remains underexplored. Here we report the formation of aqueous Cl 2 and H 2 driven by nanobubbles, achieved by introducing redox‐active HCl gas through a gas diffusion electrode without applying bias or loading catalysts. Electron paramagnetic resonance (EPR) revealed that increasing HCl intake elevates the concentration of hydroxyl radical (·OH) and hydrated electrons (e − aq ), more than an order of magnitude higher than that of feeding Ar alone. High‐resolution mass spectrometry identified spin‐trapping agent stabilized radical intermediates, including ·Cl, ClO·, and ·H. Iodometric titration estimated the equivalent Cl 2 content at approximately 18 mmol L −1 , while gas chromatography verified H 2 formation. This study demonstrates that bubbling redox‐active gases through aqueous solution can activate water reactivity, leading to the conversion of the gases themselves.