Catalyst-Free Carbon Dioxide Conversion in Water Facilitated by Pulse Discharges

By inducing CO₂-pulsed discharges within microchannel bubbles and regulating thus-forming plasma microbubbles, we observe high-performance, catalyst-free coformation of hydrogen peroxide (H₂O₂) and oxalate directly from CO₂ and water. With isotope-labeled C¹⁸O₂ as the feedstock, peaks of H₂¹⁸O¹⁶O and H₂¹⁶O₂ observed by ex situ surface-enhanced Raman spectra indicate that single-atom oxygen (O) from CO₂ dissociations and H₂O-derived OH radicals both contribute to H₂O₂ formation. The global plasma chemistry modeling suggests that high-density, energy-intense electron supply enables high-density CO₂^- (aq) and HCO₂^- (aq) formation and their subsequent coupling to produce oxalate. The enhanced solvation of CO₂, facilitated by the efficient transport of CO ionic species and CO, is demonstrated as a crucial benefit of spark discharges interacting with water at the bubble interface. We expect this plasma microbubble approach to provide a novel power-to-chemical avenue to convert CO₂ into valuable H₂O₂ and oxalic acid platform chemicals, thus leveraging renewable energy resources.