Nitrogen-doped carbon nanotubes for regulating nickel nanoparticles towards efficient electrochemical carbon dioxide reduction.

Coating transition metal nanoparticles with the carbon layer represents a highly effective strategy to modulate electronic structure for enhanced catalytic performance. Nevertheless, it is challenging for these materials to achieve the desired catalytic activity. Here, we synthesized a series of nitrogen-doped carbon nanotubes confined nickel nanoparticles (Nix@NC) through high-temperature pyrolysis to facilitate the efficient electrochemical carbon dioxide (CO2) reduction to carbon monoxide (CO). The morphology and electronic structure of Nix@NC were effectively controlled by optimizing the carbonization temperature and precursor ratios. Notably, the Ni0.10@NC sample exhibited nearly 100% selectivity for CO, with the highest CO partial current density of 499 mA cm-2, exceeding those in most previously reported works. The characterization and electrochemical analyses revealed that the Ni nanoparticles embedded within the nitrogen-doped carbon nanotubes serve as the primary active sites. The increased electrochemical active surface area and enhanced electron transfer kinetics both contributed to improved CO production. Density functional theory (DFT) calculations further revealed that the interaction between the nitrogen-doped carbon layer and Ni nanoparticles shifted the d-band center of Ni away from the Fermi level, thereby facilitating CO desorption and suppressing the competing hydrogen evolution reaction (HER).