A MOF-derived pyrrolic N-stabilized Ni single atom catalyst for selective electrochemical reduction of CO2 to CO at high current density

Abstract

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 °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–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 (FE_CO = 98.24% at −0.8 V_RHE) compared to that of Ni SAC-800 (FE_CO = 40.76% at −0.8 V_RHE). 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.