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

Abstract

Urea electrolysis is ap rospective technology for simultaneous H 2 production and nitrogen suppression in the process of water being used for energy production. Its sustainability is currently founded on innocuous N 2 products; however,w ed iscovered that prevalent nickel-based catalysts could generally over-oxidizeu rea into NO 2 À products with % 80 %F aradaic efficiencies,p osing potential secondary hazards to the environment. Trace amounts of over-oxidized NO 3À and N 2 Owere also detected. Using 15 Nisotopes and urea analogues,w ed erived an itrogen-fate network involving aN O 2 À -formation pathwayv ia OH À -assisted C À Nc leavage and two N 2 -formation pathwaysv ia intra-and intermolecular coupling.D FT calculations confirmed that C À Nc leavage is energetically more favorable.I nspired by the mechanism, ap olyaniline-coating strategy was developed to locally enrich urea for increasing N 2 production by af actor of two.T hese findings provide complementary insights into the nitrogen fate in water-energy nexus systems.

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

“…Furthermore, the IC traces of all reaction mixtures contained an additional peak, revealing that UOR led to the formation of another anionic product in high quantities (Figure 1c). In a recent report, this additional IC peak was assigned to carbonate [13b] . However, the IC system used in the present work was equipped with a suppressor for the carbonate anion (see product analysis details in Supporting Information, p. S2–S3), indicating that another anion was produced in a course of electrolysis.…”

“…Recently, Li et al [13b] . demonstrated another way to improve N 2 selectivity in UOR: polyaniline (PANI) over‐coating of activated NF allowed to increase N 2 FE by 15 % compared to bare NF.…”

Strategies for designing more efficient electrocatalysts towards the urea oxidation reaction

“…In fact, for nickel-based catalysts, N 2 produced from urea oxidation can be further over-oxidized to produce nitrogen oxide species, which are harmful for the environment. 166 Thirdly, though UOR activities can be significantly improved by applying these strategies to design advanced catalysts, their performances are still far from the requirements of real applications.…”

Electrochemical Urea Oxidation in Different Environment: From Mechanism to Devices

“…(Reproduced with permission from Ref. [76] Copyright 2021, Wiley). adsorbed À NH 2 species for further oxidization into primary NO 2 À products.…”