Crystallographically vacancy-induced MOF nanosheet as rational single-atom support for accelerating CO₂ electroreduction to CO

To attain a circular carbon economy and resolve CO2 electroreduction technology obstacles, single-atom catalysts (SACs) have emerged as a logical option for electrocatalysis because of their extraordinary catalytic activity. Among SACs, metal-organic frameworks (MOFs) have been recognized as promising support materials because of their exceptional ability to prevent metal aggregation. This study shows that atomically dispersed Ni single atoms on a precisely engineered MOF nanosheet display a high Faradaic efficiency of approximately 100% for CO formation in H-cell and three-compartment microfluidic flow-cell reactors and an excellent turnover frequency of 23,699 h(-1), validating their intrinsic catalytic potential. These results suggest that crystallographic variations affect the abundant vacancy sites on the MOF nanosheets, which are linked to the evaporation of Zn-containing organic linkers during pyrolysis. Furthermore, using X-ray absorption spectroscopy and density functional theory calculations, a comprehensive investigation of the unsaturated atomic coordination environments and the underlying mechanism involving CO* preadsorbed sites as initial states was possible and provided valuable insights.