Engineering highly-exposed nickel nanoparticles within a nitrogen-doped carbon matrix for efficient CO2 electroreduction to CO

Abstract

Ni single-atom catalysts have been widely explored for CO₂ reduction, however, their practical application is often hampered by complex synthesis and instability at high current densities. In this context, well-dispersed nickel nanoparticles present a compelling alternative, offering both facile fabrication and robust performance. Herein, a hierarchical catalyst comprising nickel nanoparticles encapsulated within a nitrogen-doped carbon shell on a hollow-rod carbon substrate (denoted as Ni_NP-BCN@C) was designed. The hollow-rod architecture maximizes the exposure of nickel nanoparticles as active sites, while the nitrogen-doped carbon shell effectively modulates the electronic environment of the metallic Ni, suppressing the competing hydrogen evolution reaction and promoting CO₂ activation. The catalyst exhibits exceptional CO₂-to-CO conversion, with a Faradaic efficiency exceeding 90% at −0.83 V vs. RHE in an H-cell and remarkable stability over 32 h. When evaluated in a flow-cell configuration, it achieves a CO Faradaic efficiency > 98% at a current density of 300 mA·cm⁻², corresponding to a high turnover frequency of ∼93,579 h⁻¹. In situ Fourier transform infrared spectroscopy revealed intensified bands for key intermediates (*COOH and COO⁻), confirming enhanced CO₂ adsorption and activation. This work showcases a scalable and efficient catalyst design, highlighting the synergy between structural engineering and electronic modulation for advanced CO₂ electroreduction.