Sustainable plasma-catalytic bubbles for hydrogen peroxide synthesis

Abstract

Hydrogen peroxide (H₂O₂) is a green oxidant widely used in various fields, from water treatment to rocket propellant. Currently, H₂O₂ is predominantly manufactured via the anthraquinone process, which requires large infrastructure investments and high energy consumption. In this study, an argon plasma-catalytic bubble process was designed to generate underwater plasma bubbles for efficient delivery of reactive species for H₂O₂ synthesis, using only water as a reactant and solar radiation as the renewable energy source. The process demonstrates unprecedented energy efficiency by employing a plasma-bubble catalytic reactor capable of operation in two discharge modes, i.e., glow and spark discharges, and using dual reactors within a single AC-circuit to mitigate energy losses around the ground electrode. The results suggest that the principal route of H₂O₂ generation is from the combination of dissolved ˙OH radicals at the plasma–liquid interface (PLI) of the forming bubbles. The dissolution of H₂O₂ formed in the gas phase also contributes to aqueous H₂O₂ generation, especially when employing humid argon. By employing a secondary reactor to utilise the lost energy around the low-voltage electrode and integrating a strongly interfacial-coupled 2D-TiO₂/2D-g-C₃N₄ photocatalyst in the glow discharge area, the achieved H₂O₂ production rate and energy efficiency of the system are 164.6 mg h⁻¹ and 9.0 g kW h⁻¹, respectively. This study provides new insights for sustainable and decentralised H₂O₂ production, and the proposed strategy can be further developed as a stand-alone or auxiliary technology in green and sustainable chemistry.