One-step Formation of Urea from Carbon Dioxide and Nitrogen Using Water Microdroplets

Water (H₂O) microdroplets are sprayed onto a graphite mesh covered with a CuBi₂O₄ coating using a 1:1 mixture of N₂ and CO₂ as the nebulizing gas. The resulting microdroplets contain urea [CO(NH₂)₂] as detected by both mass spectrometry and ¹³C nuclear magnetic resonance. This gas-liquid-solid heterogeneous catalytic system synthesizes urea in one step on the 0.1 ms time scale. The conversion rate reaches 2.7 mmol g⁻¹ h⁻¹ at 25 °C and 12.3 mmol g⁻¹ h⁻¹ at 65 °C, with no external voltage applied. Water microdroplets serve as the hydrogen source and the electron transfer medium for N₂ and CO₂ in contact with CuBi₂O₄. Water-gas and water-solid contact electrification are speculated to drive the reaction process. This strategy couples N₂ fixation and CO₂ utilization in an ecofriendly process to produce urea, converting a greenhouse gas into a value-added product.