HCl Intake via Nanobubbles Induces Redox Radicals for Aqueous Cl2 and H2 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 Cl₂ and H₂ 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 Cl₂ content at approximately 18 mmol L⁻¹, while gas chromatography verified H₂ formation. This study demonstrates that bubbling redox-active gases through aqueous solution can activate water reactivity, leading to the conversion of the gases themselves.