Synergistic electronic structure modulation in single-atomic Ni sites dispersed on Ni nanoparticles encapsulated in N-rich carbon nanotubes synthesized at low temperature for efficient CO2 electrolysis

Abstract

Ni, N-doped carbon materials (Ni–N–C) are prosperous candidates for the electrochemical CO₂ reduction reaction (CO₂RR) due to their outstanding activity and selectivity. However, the role of the coexisting uncoordinated N-doped sites and Ni nanoparticles (Ni-NPs) in overall CO₂RR has been overlooked in prior studies. To address this gap, a low temperature synthesis method developed for Ni-NP-encapsulated Ni–N–C nanotube (Ni-NCNT) catalysts with atomically dispersed Ni–N₄ and abundant uncoordinated N-doped sites, where Ni-NPs increase the electron density on Ni–N–C nanotube through carbon network and synergistically enhances the CO₂RR activity. The systematic analysis reveals the cooperative role of Ni-NPs and uncoordinated N-doped sites in altering the electronic structure of Ni–N₄ sites. The results of control experimental studies confirm the synergistic interaction of uncoordinated N-doped sites boost the CO₂RR activity of Ni–N₄ sites. Additionally, density functional theory calculations show that the strong interaction between the Ni-NPs and Ni–N–C did not affect the electronic structures of the Ni–N₄ centers, but rather alter the electronic structure of uncoordinated pyridinic-N sites. This variation led to decreased the energy barriers of rate-limiting steps of COOH* formation on Ni–N₄ and N-doped sites, resulting in excellent CO₂RR performance.