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.

Although pyrolysis of precursors is a common technique to prepare SACs, it is still a challenge to fabricate stable SACs due to their easy migration and agglomeration during this process. The key point is to develop suitable strategy to prevent metal aggregation, thus promoting the fabrication of single metal atoms to enhance the activity. 

In a study published in Research, a research team led by Prof. CAO Rong and Prof. HUANG Yuanbiao from Fujian Institute of Research on the Structure of Matter (FJIRSM) of the Chinese Academy of Sciences proposed to fabricate single-metal-atom catalyst via migration-prevention strategy. 

The researchers reported that polyaniline (PANI) was in situ inserted in the pores of iron porphyrinic-based MOF PCN-224(Fe) as a proof of concept. During pyrolysis process, the nitrogen-riched polymer PANI in the pores of PCN-224(Fe) as protective fence can prevent the aggregation of the adjacent iron species between the pores.  

Moreover, the high content of nitrogen in PANI can behave as metal trapper to catch the escaped Fe during pyrolysis process, thus produced abundant single-atom Fe-Nx sites.

They found that PANI@PCN-224(Fe)-900 turns out to be one of the most excellent oxygen reduction reaction (ORR) catalyst in both alkaline and acidic electrolyte, even surpassing commercial Pt/C because of the above-mentioned unique features. 

This study brings up a facile and general synthesis strategy to design SACs, which can guide the subsequent design of future generations of SACs. 

The migration-prevention strategy to fabricate single-atom Fe. (Image by Prof. CAO’s Group)