Controlled Synthesis of a Vacancy‐Defect Single‐Atom Catalyst for Boosting CO 2 Electroreduction

The reaction of precursors containing both nitrogen and oxygen atoms with Ni II under 500 °C can generate a N/O mixing coordinated Ni‐N 3 O single‐atom catalyst (SAC) in which the oxygen atom can be gradually removed under high temperature due to the weaker Ni−O interaction, resulting in a vacancy‐defect Ni‐N 3 ‐V SAC at Ni site under 800 °C. For the reaction of Ni II with the precursor simply containing nitrogen atoms, only a no‐vacancy‐defect Ni‐N 4 SAC was obtained. Experimental and DFT calculations reveal that the presence of a vacancy‐defect in Ni‐N 3 ‐V SAC can dramatically boost the electrocatalytic activity for CO 2 reduction, with extremely high CO 2 reduction current density of 65 mA cm −2 and high Faradaic efficiency over 90 % at −0.9 V vs. RHE, as well as a record high turnover frequency of 1.35×10 5  h −1 , much higher than those of Ni‐N 4 SAC, and being one of the best reported electrocatalysts for CO 2 ‐to‐CO conversion to date.