Rational Fabrication of Low-Coordinate Single-Atom Ni Electrocatalysts by MOFs for Highly Selective CO2 Reduction.

Single-atom catalysts (SACs) have attracted tremendous interests due to their ultrahigh activity and selectivity. However, the rational control over coordination environment of SACs remains a grand challenge. Herein, a post-synthetic metal substitution (PSMS) strategy has been developed to fabricate single-atom Ni catalysts with different N coordination numbers (denoted Ni-Nx-C) on pre-designed N-doped carbon derived from metal-organic frameworks. When served for CO2 electroreduction, the obtained Ni-N3-C catalyst achieves CO Faradaic efficiency (FE) up to 95.6%, much superior to that of Ni-N4-C. Theoretical calculations reveal that the lower Ni coordination number in Ni-N3-C can significantly enhance COOH* formation, thereby accelerating CO2 reduction. In addition, Ni-N3-C shows excellent performance in Zn-CO2 battery with ultrahigh CO FE and excellent stability. This work opens up a new and general avenue to accurate control over coordination environment of SACs for CO2 utilization.