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Regulating Coordination Environment of Single-Atom Ni Electrocatalysts Templated by MOF for Boosting CO2 Reduction.

A general synthesis and the coordination environment control of single-atom catalysts (SACs) remain great challenges. Herein, a general host-guest cooperative protection strategy has been developed to construct SACs by introducing polypyrrole (PPy) into a bimetallic metal-organic framework. As a representative, the introduction of Mg 2+ in MgNi-MOF-74 extends the spatial distance of adjacent Ni atoms; the PPy guests serve as N source to stabilize the isolated Ni atoms during pyrolysis. As a result, a series of single-atom Ni catalysts (named Ni SA -N x -C) with different N coordination numbers have been fabricated by regulating the pyrolysis temperature. Significantly, the Ni SA -N 2 -C catalyst, with the lowest N coordination number, achieves very high CO Faradaic efficiency (98%) and turnover frequency (1622 h -1 ), far superior to those of Ni SA -N 3 -C and Ni SA -N 4 -C, in electrocatalytic CO 2 reduction. Theoretical calculations reveal that the low N coordination number of single-atom Ni sites in Ni SA -N 2 -C is favorable to the formation of COOH* intermediate and thus accounts for its superior activity.