Substantially improved efficiency and selectivity of carbon dioxide reduction by superior hydrated electron in microdroplet

The photochemical conversion of CO₂ into valuable fuels faces challenges of low efficiency and poor selectivity. Hydrated electrons (e_aq^-), with their extremely negative reduction potential, are promising CO₂-reducing agents, yet their short lifetime limits selectivity and high-energy-density product formation. Herein, we show that microdroplet interfaces with strong electric fields (10⁹ volts per meter) substantially extend the lifespan of e_aq^- generated from industrial sulfite pollutants (SO₃^2-), lowering energy barriers in the CO₂ reduction reaction and enabling targeted product formation. The machine learning strategy identified microdroplet size as the key parameter controlling electric field strength, product yield, and selectivity. In our lab-based scaled-up system, microdroplets <10 micrometers improved performance by four to seven orders of magnitude over bulk-phase systems, achieving ~99% methanol selectivity. Strong interfacial electric fields stabilize intermediates and modulate carbon-oxygen bond lengths, directing pathways to high-value products. This approach enables sustainable CO₂ utilization via microdroplets, potentially producing fuels from waste.