Anuratha Krishnan Shanmugam, Rinawati Mia, Wu Tzu-Ho, Yeh Min-Hsin, Lin Jeng-Yu
Department of Chemical and Materials Engineering, Tunghai University, Taichung City 40704, Taiwan.
Department of Chemical Engineering, National Taiwan University of Science and Technology, Taipei 10607, Taiwan.
Nanomaterials (Basel). 2022 Aug 27;12(17):2970. doi: 10.3390/nano12172970.
Recently, urea electrolysis has been regarded as an up-and-coming pathway for the sustainability of hydrogen fuel production according to its far lower theoretical and thermodynamic electrolytic cell potential (0.37 V) compared to water electrolysis (1.23 V) and rectification of urea-rich wastewater pollution. The new era of the "hydrogen energy economy" involving urea electrolysis can efficiently promote the development of a low-carbon future. In recent decades, numerous inexpensive and fruitful nickel-based materials (metallic Ni, Ni-alloys, oxides/hydroxides, chalcogenides, nitrides and phosphides) have been explored as potential energy saving monofunctional and bifunctional electrocatalysts for urea electrolysis in alkaline solution. In this review, we start with a discussion about the basics and fundamentals of urea electrolysis, including the urea oxidation reaction (UOR) and the hydrogen evolution reaction (HER), and then discuss the strategies for designing electrocatalysts for the UOR, HER and both reactions (bifunctional). Next, the catalytic performance, mechanisms and factors including morphology, composition and electrode/electrolyte kinetics for the ameliorated and diminished activity of the various aforementioned nickel-based electrocatalysts for urea electrolysis, including monofunctional (UOR or HER) and bifunctional (UOR and HER) types, are summarized. Lastly, the features of persisting challenges, future prospects and expectations of unravelling the bifunctional electrocatalysts for urea-based energy conversion technologies, including urea electrolysis, urea fuel cells and photoelectrochemical urea splitting, are illuminated.
近年来，尿素电解因其理论和热力学电解池电位（0.37V）远低于水电解（1.23V）以及对富尿素废水污染的整治，而被视为一种新兴的氢燃料生产可持续途径。涉及尿素电解的“氢能经济”新时代能够有效推动低碳未来的发展。近几十年来，人们探索了众多廉价且有效的镍基材料（金属镍、镍合金、氧化物/氢氧化物、硫族化物、氮化物和磷化物），作为碱性溶液中尿素电解潜在的节能单功能和双功能电催化剂。在本综述中，我们首先讨论尿素电解的基础和基本原理，包括尿素氧化反应（UOR）和析氢反应（HER），然后讨论设计用于UOR、HER以及两者反应（双功能）的电催化剂的策略。接下来，总结了上述各种用于尿素电解的镍基电催化剂（包括单功能（UOR或HER）和双功能（UOR和HER）类型）的催化性能、机理以及包括形态、组成和电极/电解质动力学等对活性增强和降低有影响的因素。最后，阐明了在解开用于基于尿素的能量转换技术（包括尿素电解、尿素燃料电池和光电化学尿素分解）的双功能电催化剂方面持续存在的挑战、未来前景和期望的特点。
