Encapsulated Nickel Nanowires Inside Plasma-treated Single-Walled Carbon Nanotubes for Urea Oxidation

This study demonstrates a robust approach for producing Ni and Au nanowires (NWs) encapsulated by single-walled carbon nanotubes (SWCNTs), achieving lengths up to 1.2 µm. The process involves nitrogen plasma treatment to create defects in the SWCNTs, followed by the nanotubes filling with the metal precursor and its subsequent reduction. Simulations of carbon nanotube irradiation are performed to investigate the relationship between nitrogen kinetic energy and defect formation under the irradiation, revealing conditions that promote efficient nickel encapsulation. Structural analysis confirmed defect sizes ranging from 3.6 to 9.2 Å, suitable for metal precursor entry. Ni NWs exhibited excellent electrocatalytic activity in urea oxidation reactions (UOR), achieving a specific activity of 1150 A g^-1 at 1.7 V vs. reversible hydrogen electrode (RHE) in 2 M urea and stable performance over 1000 cycles. Comparative simulations of urea adsorption energies showed that nickel-filled SWCNTs enhance adsorption (-0.35 eV) when compared to pure graphene surface (-0.2 eV), demonstrating a synergistic effect of nickel and carbon structures. The role of defects in enhancing urea adsorption has also been analyzed. This work highlights the potential of SWCNTs as nano-reactors for producing high-performance catalytic materials. The findings emphasize the importance of controlled defect engineering and thermal treatment in optimizing nanowire synthesis for advanced catalytic and functional applications.