Low-coordinated Ni-N₁-C₃ sites atomically dispersed on hollow carbon nanotubes for efficient CO₂ reduction

Low-coordinated single atom catalysts compared to M-N₄ are appealing in optimized electronic structure for CO₂ electro-reduction, but the preparation is still very challenging. Herein, a novel single Ni atom catalyst with Ni-N₁-C₃ configuration is in-situ evolved on curved carbon nanotubes. The obtained Ni-N₁-C₃ catalyst exhibits a superior CO Faradaic efficiency of 97% and turnover frequency of 2,890 h⁻¹ at −0.9 V versus the reversible hydrogen electrode, as well as long-term stability over 45 h. High current densities exceeding 200 mA·cm⁻² and CO Faradaic efficiency of 99% are achieved in flow-cell. Moreover, in-situ potential- and time-dependent Raman spectra identify the key intermediates of *COOH and *CO during CO₂-to-CO conversion. Theoretical calculations reveal that the upward-shifted d-band center and charge-rich Ni sites of Ni-N₁-C₃ facilitate the electron transfer to *COOH and thus reduce the *COOH formation energy barrier. This work demonstrates a strategy for modulating the coordination environment for efficient CO₂ reduction.