A MOF-derived Pyrrolic N-stabilized Ni Single Atom Catalyst for Selective Electrochemical Reduction of CO2 to CO at High Current Density

Electrochemical reduction of CO2 to chemical fuels with a transition metal-based single atom catalyst (SAC) offers a promising strategy to reduce CO2 with high catalytic selectivity. To date, the study of atomically dispersed SACs has been mainly conducted by using a conventional H-type cell system with limited solubility of CO2 in aqueous electrolytes, resulting in large overpotentials and low current density. Here, we reported a pyrrolic N-stabilized Ni SAC with low-coordinated Ni-N-x sites by thermal activation of Ni ZIF-8, which was tested in a 3-compartment microfluidic flow cell system at the industrial level. When the pyrolysis temperature increased from 800 degrees C (Ni SAC-800) to 1000 degrees C (Ni SAC-1000), the content ratio of pyrrolic N/pyridinic N increased from 0.37 to 1.01 as well as the coordination number of Ni in Ni-N-x sites decreased from 3.14 to 2.63. Theoretical calculations revealed that the synergistic effect between the high content ratio of pyrrolic N and low-coordinated Ni can decrease the energy barrier for the desorption of *CO during the CO2RR. Therefore, Ni SAC-1000 exhibited superior catalytic performances with high CO selectivity (FECO = 98.24% at -0.8 V-RHE) compared to that of Ni SAC-800 (FECO = 40.76% at -0.8 V-RHE). Moreover, Ni SAC-1000 based on the flow cell system showed a higher current density (similar to 200 mA cm(-2)) compared to that of the H-type cell system (similar to 20 mA cm(-2)). As a result, this study experimentally demonstrated that the pyrrolic N-stabilized and low-coordinated Ni SAC-1000 in the microfluidic flow cell reactor provides great chances for scaling up the productivity of the CO2RR at the industrial level.