Advances in Catalytic Electrooxidation of Urea: A Review

Abstract

The urea oxidation reaction (UOR) is technologically important for the development of a renewable energy infrastructure. Urea electrolysis (UE) can be used to produce hydrogen much more cost‐effectively than water electrolysis, as it theoretically requires 93% less energy. Urea can also be used as fuel in direct urea fuel cells (DUFCs), instead of H2, and thus serve as an efficient hydrogen carrier. This review addresses the UOR in neutral, acidic, and alkaline electrolytes, with special emphasis on the latter. Recent developments in Ni‐based catalysts for urea oxidation (UO) in alkaline electrolytes are discussed in detail, highlighting proposed reaction mechanisms and intermediates, based on experimental and computational results. Various catalytic designs used to mitigate the UO kinetic barriers, including the use of transition metal oxides and alloys, as well as tailored surface support materials, and discuss their application in UE and DUFCs are presented. The significant challenges impeding advances in urea electrocatalysis, in addition to emerging research areas in this field, are also discussed.

Strategies for designing more efficient electrocatalysts towards the urea oxidation reaction

“…In fact, till now, few acidic UOR catalysts have been reported. 72 Since NaCl is one of the main components in real urine, urea oxidation in neutral NaCl medium was also investigated before. 73,74 For neutral UOR performed in NaCl electrolyte, Cl − is first oxidized to Cl 2 , and then the obtained Cl 2 is disproportionated to produce HClO and Cl − .…”

An Unveiled Electrocatalysis Essence of NiCo Hydroxides through in Situ Raman Spectroscopy for Urea Oxidation

“…Nitrogen‐based fuels such as ammonia and urea have also been well accepted as clean energy carriers with high‐energy densities. [ 7–9 ] To this end, the electrochemical utilization of urea for providing electrons for reductive half reactions, that is, urea oxidation reaction (UOR; CO(NH 2 ) 2 + 6OH − = N 2 + CO 2 + 5H 2 O + 6e − ), has been attracting extensive attention.…”

One-pot hydrothermal synthesis of Co–Ni hexacyanoferrate nanocuboids on Ni-foam as efficient catalysts for oxygen evolution and urea oxidation reactions

“…It is largely limited by its slow kinetics and requirement of high voltages and catalysts to promote the reaction [1,2]. The OER can be promoted by replacing the anodic oxidation reaction with other oxidation reactions, such as the oxidation of urea, methanol, and ethanol, which require less potential than the OER [3][4][5][6][7][8]. The electrolysis of urea offers much easier access to hydrogen owing to its lower overpotential (0.37 V) compared to the electrolysis of water (1.23 V) and high gravimetric concentration (6.71%) of hydrogen.…”