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 (eaq-), 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 eaq- generated from industrial sulfite pollutants (SO32-), 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.