Electrochemical Urea Oxidation in Different Environment: From Mechanism to Devices

Abstract

Urea has been regarded as an important chemical compound in the food‐water‐energy nexus. However, the emission of urea from human activity, industrial manufacture, and agricultural fertilization into the environment has caused an ecological nitrogen imbalance. Besides addressing the environmental pollution, the applications of clean energy conversion from urea‐rich wastewater has strong potential for resource and energy recovery. Herein, we conducted a comprehensive overview of electrochemical urea oxidation reaction (UOR) for pollution control and energy harvesting. The present mechanisms and behaviors of UOR under different water matrices have been characterized and compared in detail. Additionally, the latest development of electrochemical UOR integrated into electrolyzers and fuel cells are presented. Finally, we discuss the prospects and challenges of UOR technologies, suggesting several directions for the electrochemical conversion of urea‐abundant wastewater in the near future.

Unconventional Phase Synergies with Doping Engineering Over Ni Electrocatalyst Featuring Regulated Electronic State for Accelerated Urea Oxidation

“…Besides, the electrocatalytic UOR behaviors of the noble‐metal‐based materials were also evaluated. As depicted in Figure S4, both commercial Pt/C and Pt plate (1×1 cm 2 ) exhibit negligible catalytic activities for the UOR, in accordance with previous reports [1a,f] …”

“…In the present study, our delicately proposed hcp‐MnNi/NC, with unconventional hcp phase and Mn species incorporation, is capable of performing as a type of advanced electrocatalyst for the UOR. Impressively, with outstanding activity and fast kinetics (1.30 V vs. RHE at the current density of 10 mA cm −2 and Tafel slope of 30.2 mV dec −1 ), the hcp‐MnNi/NC proposed here can favorably rival the state‐of‐the‐art UOR electrocatalysts [1f,3a,4a–c,9a,12a,28] . A detailed comparison with other recently reported UOR catalysts is given in Figure S7 and Table S1.…”

Solar‐Driven Catalytic Urea Oxidation for Environmental Remediation and Energy Recovery

“…The theoretical OCV between pair reactions of urea oxidation and oxygen reduction could be estimated as 1.147 V. Actually, many other substrates with more favorable cathodic half‐reactions can show faster reaction kinetics and better outcome voltage compared with oxygen reduction, such as hydrogen peroxide (H 2 O 2 ) and peroxymonosulfate (PMS). Employing H 2 O 2 in the basic electrolyte at the cathodic chamber elevated the theoretical OCV of a photocatalytic urea‐based fuel cell to 1.626 V while substituting with PMS reduction half‐reaction could further raise it to 2.566 V, almost twice that of oxygen or air employed as oxidant [77] . Although the practical OCV obtained at present is still far more satisfying, it demonstrates that there are more possibilities and room to improve the performance with an optimal and efficient configuration system that efficiently promotes the power density and outcome.…”

Replacing Anodic Oxygen Evolution Reaction with Organic ­Oxidation: The Importance of Metal (Oxy)Hydroxide Formation as the Active Oxidation Catalyst

“…52 Urea is rich in hydrogen content with a high energy density ~16.9 MJ L -1 . 53 The urea oxidation in the fuel cell converts the chemical energy into electricity. 53 The electrooxidation of urea results in the generation of H2 as well as it helps in the water purification by removing urea from water.…”

“…53 The urea oxidation in the fuel cell converts the chemical energy into electricity. 53 The electrooxidation of urea results in the generation of H 2 as well as it helps in the water purification by removing urea from water. 53 The electrocatalytic oxidation of benzylamine leads to the formation of oximes, imines, amides, nitriles, amine oxides, and azo compounds that are used in agrochemical, natural products, and pharmaceuticals industries.…”