Coupling NiMn-Layered Double Hydroxide Nanosheets with NiCo₂S₄ Arrays as a Heterostructure Catalyst to Accelerate the Urea Oxidation Reaction

Abstract

The rational design of advanced transition-metal-based electrocatalysts with a heterostructure is a promising strategy for the promotion of the urea oxidation reaction (UOR) for energy-conservation technologies, but achieving a sufficiently high performance remains a challenge. In this work, we report a dramatic improvement in the UOR performance of a heterostructured electrocatalyst that combines NiMn-layered double hydroxide (LDH) nanosheets with NiCo2S4 arrays via a series of facile hydrothermal fabrication steps. Due to the high-flux electron transfer pathways at the close-contact interface, abundant active sites, and unique three-dimensional (3D) architecture, the NiCo2S4@NiMn LDH heterostructure grown on nickel foam exhibits a low potential of 1.37 V at a current density of 100 mA·cm–2 and a low Tafel slope of 43.8 mV·dec–1. More impressively, the proposed electrocatalyst demonstrates robust stability of more than 25 h at a current density of 50 mA·cm–2 with a negligible decrease in activity. In addition, density functional theory calculations reveal that the interface engineering within the heterostructure is beneficial for the adsorption and activation of urea molecules and the improvement of the sluggish UOR dynamics. The dissociation of adsorbed CO(NH2)2* into CO* and NH* intermediates on the heterostructured NiMn LDH is also facilitated by electronic coupling with NiCo2S4, resulting in superior UOR performance.

CoFe-Layered Double Hydroxide Needles on MoS2/Ni3S2 Nanoarrays for Applications as Catalysts for Hydrogen Evolution and Oxidation of Organic Chemicals

“…Due to the increasing environmental concerns and global demand for sustainable energy, it is imperative to investigate alternative sources of eco-friendly and renewable energy as a substitute for conventional fossil fuels. − Electrolysis of water has received significant attention owing to its potential to continuously produce hydrogen and replace fossil fuels through a sustainable process. − However, the efficiency of water electrolysis is often hindered by the sluggish oxygen evolution reaction (OER), which is inhibited by the steps of O–O bond formation and O–H bond breaking with slow reaction kinetics. − In recent years, oxidation reactions of organic molecules (such as urea, ethanol, and hydrazine) have been considered an alternative to OER owing to favorable thermodynamic potentials. − The urea oxidation reaction (UOR) exhibits better thermodynamic favorability than OER, with a lower theoretical potential ( E = 0.37 V vs the reversible hydrogen electrode (RHE)) compared to that of OER ( E = 1.23 V vs RHE). − However, the process of urea electro-oxidation still involves a complex six-electron-transfer step, which also imposes significant limitations on the reaction kinetics. , It is worth noting that one urea molecule comprises an electron-donating amino group (−NH 2 ) and an electron-withdrawing carbonyl group (–CO), which tends to adsorb onto distinct catalytic sites to generate crucial intermediates (CO* and NH*) upon breaking the CO bond. , It plays a vital role in the electro-oxidation reaction of urea. Hence, it is imperative to design a rational electrocatalyst to promote the dissociation of urea.…”