A high-energy hydrogen radical initiates efficient electrosynthesis of urea from CO2 and N2

Abstract

The electrochemical co-reduction of CO2 and N2 to urea presents a sustainable alternative to conventional synthesis but faces substantial challenges. Here we design a catalyst by anchoring the ionic liquid (IL) 1-ethyl-2,3-dimethylimidazolium bromide onto a CuBi surface. The IL@CuBi catalyst delivers an exceptional Faradaic efficiency toward urea (FEurea) of 73.0% and a current density of 27.4 mA cm−2 in an H-type cell, with a production rate of 124.7 μmol cm−2 h−1. Detailed study indicates that during the co-reduction process, Emmim+ cations on IL@CuBi are first reduced to Emmim· radicals, which transfer electrons to H+ to generate H· radicals. This relayed electron-transfer pathway for H· radical generation bypasses the conventional formation from surface-adsorbed *H intermediates, thereby effectively suppressing the hydrogen evolution reaction. The generated H· radicals, acting as high-energy bullets, directly participate in subsequent hydrogenation steps, thereby substantially reducing the free energy barrier and enhancing reaction kinetics.