Atomically Dispersed Transition Metals on Carbon Nanotubes with Ultrahigh Loading for Selective Electrochemical Carbon Dioxide Reduction

Single-atom catalysts (SACs) are the smallest entities for catalytic reactions with projected high atomic efficiency, superior activity, and selectivity; however, practical applications of SACs suffer from a very low metal loading of 1-2 wt%. Here, a class of SACs based on atomically dispersed transition metals on nitrogen-doped carbon nanotubes (MSA-N-CNTs, where M = Ni, Co, NiCo, CoFe, and NiPt) is synthesized with an extraordinarily high metal loading, e.g., 20 wt% in the case of NiSA-N-CNTs, using a new multistep pyrolysis process. Among these materials, NiSA-N-CNTs show an excellent selectivity and activity for the electrochemical reduction of CO₂ to CO, achieving a turnover frequency (TOF) of 11.7 s^-1 at -0.55 V (vs reversible hydrogen electrode (RHE)), two orders of magnitude higher than Ni nanoparticles supported on CNTs.