(705g) Unveiling the Role of Transition-Metal Dopants in Ni(OH)2/NiOOH-Catalyzed Urea Oxidation

Urea is a common waste in agriculture runoff and has also been proposed as a splitting target in urea electrolysis to achieve hydrogen production from wastewater. However, the overpotential of electrochemical urea oxidation reaction (UOR) is high due to the complicated six-electron transfer oxidation process on most metal catalysts, the competition with OER further limits catalyst options for UOR. The most promising and studied catalysts for UOR are Ni-based catalysts. Previous theoretical and experimental studies have been focused on NiOOH step-edges as active sites for UOR. Here we focus on the more abundant basal-type sites on NiOOH for UOR and study the effects of metal doping on the transition from Ni(OH)₂ to NiOOH and urea oxidation pathway using density functional theory (DFT) calculations. We study different Ni(OH)₂ and NiOOH (001) surfaces with oxygen vacancy and dopants including Mn, Fe, Co, and Cu and examine how the doping elements influence the Ni-catalysts transition and the urea oxidation. The introduction of Fe dopant not only facilitates the formation of catalytically active NiOOH phase, but also favors the adsorption of urea over undoped NiOOH surface, thereby significantly benefitting the overall UOR. Moreover, we gain a fundamental understanding of the competition between UOR and OER and how the dopants influence the reaction selectivity. This work sheds light on the structure-property relationship of Ni-catalysts in urea oxidation and provides design principles for functional Ni-based materials, which will help accelerate the development of efficient UOR catalysts.