Reversed I1Cu4 single- atom sites for superior neutral ammonia electrosynthesis with nitrate

Electrochemical ammonia (NH3) synthesis from nitrate reduction (NITRR) offers an appealing solution for addressing environmental concerns and the energy crisis. However, most of the developed electrocatalysts reduce NO3- to NH3 via a hydrogen (H*)- mediated reduction mechanism, which suffers from undesired H*- H* dimerization to H2, resulting in unsatisfactory NH3 yields. Herein, we demonstrate that reversed I1Cu4 single- atom sites, prepared by anchoring iodine single atoms on the Cu surface, realized superior NITRR with a superior ammonia yield rate of 4.36 mg h -1 cm-2 and a Faradaic efficiency of 98.5% under neutral conditions via a proton- coupled electron transfer (PCET) mechanism, far beyond those of traditional Cu sites (NH3 yield rate of 0.082 mg h -1 cm-2 and Faradaic efficiency of 36.5%) and most of H*- mediated NITRR electrocatalysts. Theoretical calculations revealed that I single atoms can regulate the local electronic structures of adjacent Cu sites in favor of stronger O- end- bidentate NO3 - adsorption with dual electron transfer channels and suppress the H* formation from the H2O dissociation, thus switching the NITRR mechanism from H*- mediated reduction to PCET. By integrating the monolithic I1Cu4 single- atom electrode into a flow- through device for continuous NITRR and in situ ammonia recovery, an industrial- level current density of 1 A cm-2 was achieved along with a NH3 yield rate of 69.4 mg h -1 cm-2. This study offers reversed single- atom sites for electrochemical ammonia synthesis with nitrate wastewater and sheds light on the importance of switching catalytic mechanisms in improving the performance of electrochemical reactions.