Deciphering and Suppressing Over-Oxidized Nitrogen in Nickel-Catalyzed Urea Electrolysis

Urea electrolysis is a prospective technology for simultaneous H production and nitrogen suppression in the process of water being used for energy production. Its sustainability is currently founded on innocuous N products; however, we discovered that prevalent nickel-based catalysts could generally over-oxidize urea into NO products with ≈80 % Faradaic efficiencies, posing potential secondary hazards to the environment. Trace amounts of over-oxidized NO and N O were also detected. Using N isotopes and urea analogues, we derived a nitrogen-fate network involving a NO -formation pathway via OH -assisted C-N cleavage and two N -formation pathways via intra- and intermolecular coupling. DFT calculations confirmed that C-N cleavage is energetically more favorable. Inspired by the mechanism, a polyaniline-coating strategy was developed to locally enrich urea for increasing N production by a factor of two. These findings provide complementary insights into the nitrogen fate in water-energy nexus systems.