Noble metals (e.g., platinum) are often used as catalysts in the oxygen reduction reaction (ORR) of fuel cell cathodes. However, the drawbacks, such as the high cost, easy to be poisoned by CO, and poor stability, obviously limit their industrialization and application. Therefore, it is urgent to develop a new type of oxygen reduction catalysts to replace platinum.
Nitrogen-doped porous carbon supported single atom catalysts (SACs) have become one of the most promising alternatives to precious metal catalysts in ORR due to their unique geometric/electronic structures and outstanding performances, especially the Fe/Co SACs. However, most of them involve tedious pre- and/or post-treatments, especially derived from porphyrin-based materials, which would increase the operation difficulty, even mislead the relationship between structures and activities of the catalysts.
Therefore, the rational design of synthesis route, the achievement of the high efficiency in electrocatalytic reactions and the exploration of the catalytic mechanism and active sites, have become one of the research focus of SACs in fuel cells.
Very recently, the group of Professor Hongbing Ji and Dr. Xiaohui He in Fine Chemical Industry Research Institute of Sun Yat-sen University demonstrated a facile precursor-dilution strategy to prepare nitrogen-doped porous carbon supported Fe SACs through the Schiff-based reaction via co-polycondensation of amino-porphyrin materials, followed by pyrolysis at high temperature.
According to the aberration corrected high-angle annular dark-field scanning transmission electron microscopy and synchrotron radiation, which determined that the Fe atom was atomically dispersed in the support and forming a FeN4O-like structure. It is superior to commercial 20 wt% Pt/C in terms of ORR activities, stability, and methanol resistance in alkaline condition, and moderate ORR activities under the acidic condition.
The structure-activity relationship and catalytic mechanism of the catalyst was further verified by KSCN poisoning, CO poisoning and catalytic activity comparison with reference sample (pure carbon supports without metal loadings, iron nanoclusters, and iron nanoparticles), which confirmed that the active centers of electrocatalytic oxygen reduction were atomically dispersed Fe species.