As an alternative energy, hydrogen can be converted into electrical energy via direct electrochemical conversion in fuel cells. One important drawback of full cells is the sluggish oxygen reduction reaction (ORR) promoted by the high-loading of platinum-group-metal (PGM) electrocatalysts. Fe-N-C family has been received extensive attention because of its low cost, long service life and high oxygen reduction reaction activity in recent years. In order to further enhance the ORR activity, the synthesis method, morphology regulation and catalytic mechanism of the active sites in Fe-N-C catalysts are investigated. This paper reviews the research progress of Fe-N-C from nanoparticles to single atoms. The structure-activity relationship and catalytic mechanism of the catalyst are studied and discussed, which provide a guidance for rational design of the catalyst, so as to promote the more reasonable design of Fe-N-C materials.

The identification of highly active heterogeneous catalysts to replace their homogeneous counterparts remains a challenge in the case of organic catalysts, especially polymers, in highly viscous reaction systems. In this work, we designed and synthesized a novel, solid-supported, and heterogeneous pseudo-single atom Pt catalyst with high activity and recyclability. Superparamagnetic Fe₃O₄-SiO₂ core–shell nanoparticles (NPs) were used as the substrate. The functionalization of the SiO₂ shell with silane coupling agents containing vinyl groups allows stabilizing Pt on the SiO₂ surface through complexation. The as-prepared pseudo-single atom Pt displays high activity in the hydrosilylation of allyl-terminated polyether with polymethylhydrosiloxane and could be easily collected by applying a magnetic field. The Pt/vinyl/SiO₂/Fe₃O₄ catalyst can be reused for up to four reaction cycles without appreciable decrease in activity. This work demonstrates a novel strategy for the design of pseudo-single atom noble metal catalysts for processes in high-viscosity media.