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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 CO to CO, achieving a turnover frequency (TOF) of 11.7 s at -0.55 V (vs reversible hydrogen electrode (RHE)), two orders of magnitude higher than Ni nanoparticles supported on CNTs.

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A flexible, dictyophora-like sponge of porous N-doped carbon microtubes demonstrates excellent electrocatalytic activities for both the oxygen reduction reaction and oxygen evolution reaction.

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The development of efficient Fe−N−C materials enriched with single-atom Fe sites toward the oxygen reduction reaction (ORR) is still a great challenge because Fe atoms are mobile and easily aggregate into nanoparticles during the high-temperature treatment. Herein, we proposed a facile and universal secondary-atom-assisted strategy to prepare atomic iron sites with high density hosted on porous nitrogen-doped carbon nanowires (Fe−NCNWs). The Fe−NCNWs showed an impressive half-wave potential (E 1/2 ) of 0.91 V and average kinetic current density (J K ) of 6.0 mA cm −2 at 0.9 V in alkaline media. They also held a high ORR activity in acidic solution with the E 1/2 of 0.82 V and average J K of 8.0 mA cm −2 at 0.8 V. Density functional theory calculations demonstrated that the high ORR activity achieved is originated from single-atom iron sites that decrease the energy barrier in the reaction path efficiently.

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