Single-atom catalysts (SACs) have attracted broad research interest as they combine the merits of both homogeneous and heterogeneous catalysts, such as maximized atom utilization efficiency, highly catalytic activity and recyclability. However, it is still a great challenge to fabricate stable SACs because of their easy migration and agglomeration.

In a study published online in ACS Energy Letters, the research group led by Prof. CAO Rong at Fujian Institute of Research on the Structure of Matter (FJIRSM) of Chinese Academy of Sciences developed a simple ionothermal method to fabricate atomically dispersed Fe−N_x species on porous porphyrinic triazine-based frameworks (FeSAs/PTF) with high Fe loading up to 8.3 wt %.

The researchers performed spherical aberration-corrected transmission electron microscopy to prove the atomically dispersed iron atoms and exclude the existence of iron nanoparticles. Through element mapping, they revealed that elements Fe, N and C were homogeneously distributed over the entire catalyst.

In addition, they conducted X-ray absorption near-edge structure (XANES) and extented X-ray absorption fine structure (EXAFS) to further prove the atomically dispersed iron atoms and determine the coordination environment of Fe species. It turned out that each Fe atom in FeSAs/PTF-600 is coordinated with four nitrogen atoms, thus forming the Fe-N₄ active sites.

The as-prepared catalyst FeSAs/PTF-600 synthesized at 600 ^oC with atomically dispersed Fe-N₄ active sites and good electrical conductivity exhibited highly efficient activity, methanol-tolerance and superstability for oxygen reduction reaction (ORR) in both alkaline and acidic conditions.

This study brought up a facile and general synthesis strategy to design SACs with exact atomistic structure of the active sites, and further established a definitive correlation between the active sites and catalytic properties, which can guide the subsequent design of future generations of SACs.