Promoting Electroreduction of CO2 and NO3− to Urea via Tandem Catalysis of Zn Single Atoms and In2O3-x

Urea electrosynthesis from co-electrolysis of CO₂ and NO₃⁻ (UECN) offers an innovative route for converting waste CO₂/NO₃⁻ into valuable urea. Herein, Zn single atoms anchored on oxygen vacancy (OV)-rich In₂O_3-x (Zn₁/In₂O_3-x) are developed as a highly active and selective UECN catalyst, delivering the highest urea yield rate of 41.6 mmol h⁻¹ g⁻¹ and urea-Faradaic efficiency of 55.8% at −0.7 V in flow cell, superior to most previously reported UECN catalysts. In situ spectroscopic measurements and theoretical calculations unveil the synergy of In/Zn₁ sites and OVs in promoting the UECN process via a tandem catalysis mechanism, where Zn₁-OV site activates NO₃⁻ to form ^*NH₂ while In-OV site activates CO₂ to form ^*CO. The formed ^*CO spontaneously migrates from the In-OV site to the nearby Zn₁-OV site and then couples with ^*NH₂ to generate ^*CONH₂ which is ultimately converted into urea.