Ni-based electrocatalysts for urea oxidation reaction: mechanism, catalyst design strategies and future perspectives

Abstract

Untreated urea-rich wastewater exerts severe adverse impacts on both the environment and human health, prompting extensive attention towards the urea oxidation reaction (UOR) as a sustainable technology to generate clean energy in recent years. UOR has a thermodynamic advantage over oxygen evolution reaction (OER) (1.23 V vs reversible hydrogen electrode, RHE) and only requires 0.37 V (vs RHE), which is considered as an effective alternative to H₂ production by water electrolysis. However, the inevitable kinetic slowness and complex adsorption/desorption during process, hindering its practical application. Most traditional catalysts utilized for the UOR are comprised of precious metals, resulting in limited economic viability. Inspired by natural ureases, Ni-based catalysts have emerged as promising alternatives owing to their rich deposits, low cost, and the regulated d orbitals of transition metal Ni, demonstrating considerable potential for UOR. Currently, numerous studies have explored Ni-based hydroxides, oxides, chalcogenides, and phosphides in alkaline solutions. In this review, we will explore the UOR reaction mechanism and summarize the catalyst design strategies of various Ni-based catalysts recently, especially Ni-MOF, which has been rarely discussed before. Then, the broad prospects of UOR in practical applications are summarized. Finally, based on the design strategies and performance comparisons discussed above, the challenges and prospects facing the future development of Ni-based electrocatalysts for the UOR will be presented.