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

The electrochemical urea oxidation reaction (UOR) to N2 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 NOx− usually dominates over its oxidation to N2 at Ni(OH)2‐based anodes...

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Published in:Angewandte Chemie International Edition 2022-09, Vol.61 (39), p.e202209839-n/a
Main Authors: Tatarchuk, Stephen W., Medvedev, Jury J., Li, Feng, Tobolovskaya, Yulia, Klinkova, Anna
Format: Article
Language:English
Subjects:
Catalysts
Computer applications
Cyanates
Electrocatalysis
Electrochemistry
Electrolysis
Nickel
Nickel compounds
Nitrogen oxides
Nitrogen removal
Overoxidation
Oxidation
Reaction Mechanism
Reaction mechanisms
Selectivity
Urea
Urea Electrolysis
Ureas
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Summary:The electrochemical urea oxidation reaction (UOR) to N2 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 NOx− usually dominates over its oxidation to N2 at Ni(OH)2‐based anodes. Furthermore, detailed reaction mechanisms of UOR remain unclear, hindering the rational catalyst design. We found that UOR to NOx− on Ni(OH)2 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 NOx− and N2 follows two distinct vacancy‐dependent pathways. We also demonstrate that the reaction selectivity can be steered towards N2 formation by altering the composition of the catalyst, e.g., doping the catalyst with copper (Ni0.8Cu0.2(OH)2) increases the faradaic efficiency of N2 from 30 % to 55 %. Urea electrooxidation to N2 is a promising anodic process for producing renewable fuels at the cathode. However, Ni(OH)2‐catalyzed urea oxidation predominantly produces a ≈1 : 1 mixture of nitrite+cyanate, with N2 being a minor product. A mechanistic analysis suggests that the binding site availability for both N atoms in urea is crucial for reaction selectivity. Doping Ni(OH)2 with Cu significantly suppresses the cyanate+nitrate pathway.
ISSN:1433-7851
1521-3773
DOI:10.1002/anie.202209839