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 microenvironment 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-N_x -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 coordination microenvironment modulation (MEM) of SACs for CO₂ utilization.