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–Nx 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 °C (Ni SAC-800) to 1000 °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–Nx 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 VRHE) compared to that of Ni SAC-800 (FECO = 40.76% at −0.8 VRHE). Moreover, Ni SAC-1000 based on the flow cell system showed a higher current density (∼200 mA cm−2) compared to that of the H-type cell system (∼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.