3D Hierarchical NiCo Layered Double Hydroxide Nanosheet Arrays Decorated with Noble Metal Nanoparticles for Enhanced Urea Electrocatalysis

Abstract

The electrocatalysis of urea represents an important potential as an efficient technology for sustainable energy development. This anodic reaction generates hydrogen or electrical power through direct electrooxidation of urea molecules, but is greatly inhibited by its slow kinetics. Therefore, tailoring highly efficient, earth‐abundant, and durable electrocatalysts for urea oxidation reaction (UOR) is a fundamental for the enhancement of green energy conversion technologies. Herein, we report a scalable synthetic strategy to construct three‐dimensional (3D) nickel‐cobalt layered double hydroxide nanosheet arrays (NiCo−LDH NSAs) with silver (Ag0) or gold (Au0) and palladium (Pd0) intercalants as high performance catalysts for UOR. Experimental results suggest that the interlayer spacing of multi‐anions LDH NSAs can effectively afford synergetic effects of increased electrochemical surface area, better exposure of catalytically active sites, and favorable adsorption energy of urea molecules. As expected, the deposition of noble metal nanoparticles (NPs) could successfully modulate the electronic structure, delivering a rise to significantly improved UOR activity. Specifically, the Au/NiCo−LDH hybrid exhibits a superior electro‐catalytic performance toward urea electrooxidation with a highest current. These findings offer an effective pathway to prepare potential earth‐abundant electrocatalysts for direct urea fuel cells (DUFCs).

Carbon Anchored Epitaxially Grown Nickel Cobalt‐Based Carbonate Hydroxide for Urea Electrooxidation Reaction with a High Activity and Durability

“…Moreover, the performance of pure NiCo CHs was also tested under similar conditions. Both catalytic layers exhibit redox peaks ascribed to the redox reactions of Ni 2+ /Ni 3+ and Co 2+ /Co 3+ /Co 4+ . It is worth to note that the redox peaks of C−NiCo CHs catalyst are much larger than those of mixed NiCo CHs, implying that the composite possesses a higher electrochemical activity.…”

“…Figure B shows the CVS of multicomponent C−NiCo CHs and mixed NiCo CHs catalysts in 1 M KOH aqueous solution with 0.33 M urea at 10 mVs −1 . Noticeably, the current density of both electrodes in the anodic branch could be boosted as a result of urea electrocatalysis by the redox cycling between Ni 3+ /Ni 2+ and Co 2+ /Co 3+ /Co 4+ at the catalyst/electrolyte heterointerfaces . A slight current peak can be clearly seen in the cathodic sweep, demonstrating the transformation of unreacted NiOOH species into inactive Ni(OH) 2 .…”

“…On the other hand, previous studies declared that cobalt ions also participate in the electrocatalysis process of urea, but with a humble activity originated from the occurrence of Co 4+ /Co 3+ active sites . Impressively, the porous features of the designated C−NiCo CHs composite with multiple open spaces among the adjoining nanorods ensure a facile release of formed gasses, resulting in better kinetics.…”

“…In fact, the catalysis of urea with a higher oxidation state of nickel is much favorable than Ni 2+ (Figure S8B). In addition, the cobalt doping causes structural defects and edge sites, which enable abundant electrocatalytic sites for UOR …”

Electrocatalytic Properties of 3D Hierarchical Graphitic Carbon–Cobalt Nanoparticles for Urea Oxidation

“…Then, there was no enhancement in current intensity above 0.3 M, suggesting saturation kinetics at the CoGC electrode. 73 The linear relation was found to be i (mA) = 0.83492 × C urea (mM) + 0.26012 and correlation R 2 = 0.90 ( Figure S3 ).…”