Gram-scale synthesis of single-atom metal–N–CNT catalysts for highly efficient CO2 electroreduction†

Abstract

Single-atom catalysts (SACs) have attracted much interest for electrochemical CO₂ reduction because of their high metal utilization and excellent catalytic activity. However, the practical applications of SACs were restricted by the low production yield. Herein, we developed a facile synthetic strategy for fabricating metal–nitrogen–carbon nanotube (M–N–CNT, M = Ni, Co, Cu, Fe, Mn, Zn, Pt, or Ru) SACs at scale (>1 g) by direct pyrolysis of metal cations, phenanthroline and CNTs at high temperature. The pyrolysis leads to forming coordinated Ni–N active sites anchored on CNTs. The prepared Ni–N–CNT catalyst with a remarkable Ni loading of 2 wt% determined by ICP exhibits the highest activity for CO₂-to-CO conversion with a high faradaic efficiency of 94% and excellent stability. Aberration-corrected high-angle annular dark-field transmission electron microscopy, X-ray photoelectron spectroscopy and X-ray absorption spectroscopy confirm the presence of isolated Ni single atoms in Ni–N–CNT, which act as the active centers for CO₂ electroreduction while the CNT support offers fast pathways for electron and mass transports. This work laid foundations for future practical applications in CO₂ electroreduction, oxygen reduction reactions, water splitting and nitrogen reduction and beyond.