Abstract
Electrochemical oxidation of urea (UOR) is critical in the removal of urea from wastewater and energy conservation and storage. Nickel-based catalysts are widely used for urea-ORR, but in all cases, the nickel must be hybridized with carbon materials to improve its conductivity. In this manuscript, we demonstrate the synthesis of a nickel-decorated carbon nanotube (Ni-NCNT) by simple microwave pyrolysis of Dabco (1,4-diazabicyclo[2.2.2]octane)-based coordination polymer frameworks (CPF). The surface structure, morphology and chemical composition of Ni-NCNT were characterized by Raman spectrum, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy and energy-dispersive X-ray spectroscopy (EDS) analysis. SEM studies showed micrometer-long bamboo-shaped CNTs with nickel nanoparticles anchored to the walls and inside the nanotubes. A structural study by TEM and Raman spectra showed that carbon nanotubes are rich in defects due to the presence of nitrogen, and this was confirmed by energy-dispersive X-ray spectroscopy (EDS) maps. When applied as electrocatalysts in urea oxidation reactions (UOR), our newly developed Ni-NCNT shows excellent electrocatalytic activity and stability, making it a versatile catalyst in energy generation and mitigating water contamination.
Highlights
With increasing urbanization, there is a tremendous increase in the release of urearich wastewater, which is harmful to the environment and public health
Careful high-resolution transmission electron microscopy (TEM) analysis of CNTs (Figure 1d) revealed that the nanotubes had partitioned, but inter-connected hollow compartments and the walls of the tubes were curved with defects in the outermost few layers, whereas the inner walls were defect-free and irregular shaped nickel nanoparticles were core-shell structured with thin carbon coating
The shells were uniform in thickness and estimated to be in the range of 27–32 layers, with the outer 3–4 layers showing a d-spacing of 0.36 nm, whereas the remaining inner layers had a d-spacing of 0.34 nm, typical of graphite (002) planes
Summary
There is a tremendous increase in the release of urearich wastewater, which is harmful to the environment and public health. When compared to other liquid fuels, urea possesses excellent oxidation thermodynamics, and the primary urea oxidation reaction (UOR) and the half-wave potential determine the performance of DUFC. The electrochemical technique is very promising for urea oxidation and elimination; the reaction kinetics of urea oxidation are relatively slow due to the so-called ‘six-electron transfer process’ occurring at the anode [10,11]. Noble metal catalysts such as Pt [12,13] and Ru [14]-based catalysts can improve the catalytic performance of urea oxidation, but their high cost and scarcity limit their large-scale industrial application, which necessitates the need to find more efficient and cost-effective electrocatalysts for UOR
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