Nickel-Catalyzed Urea Electrolysis: From Nitrite and Cyanate as Major Products to Nitrogen Evolution.

The electrochemical urea oxidation reaction (UOR) to N represents an efficient route to simultaneous nitrogen removal from N-enriched waste and production of renewable fuels at the cathode. However, the overoxidation of urea to NO usually dominates over its oxidation to N at Ni(OH) -based anodes. Furthermore, detailed reaction mechanisms of UOR remain unclear, hindering the rational catalyst design. We found that UOR to NO on Ni(OH) is accompanied by the formation of near stoichiometric amount of cyanate (NCO ), which enabled the elucidation of UOR mechanisms. Based on our experimental and computational findings, we show that the formation of NO and N follows two distinct vacancy-dependent pathways. We also demonstrate that the reaction selectivity can be steered towards N formation by altering the composition of the catalyst, e.g., doping the catalyst with copper (Ni Cu (OH) ) increases the faradaic efficiency of N from 30 % to 55 %.