Atomically dispersed Fe-N-C catalysts with highly symmetric FeN₄ structures have emerged as promising candidates for the electrocatalytic oxygen reduction reaction (ORR) and related industrial applications, such as hydrogen fuel cells and zinc-air batteries. However, immobilizing active sites on commonly used carbon supports (e.g., XC-72, activated carbon, and carbon nanotubes) often leads to mass transfer limitations, resulting in reduced efficiency and increased costs. In this work, we achieve the in-situ formation of topological carbon defects around FeN₄ moieties via a multi-step carbonization strategy, yielding a TDNC@Fe₁ catalyst with a unique structural configuration. Benefiting from the robust coupling between atomically dispersed Fe-N₄ active sites and topologically defective N-doped carbon (TDNC), the resultant TDNC@Fe₁ catalyst exhibits a remarkable half-wave potential of 0.901 V in 0.1 M KOH, outperforming commercial Pt/C (0.857 V) and most reported catalysts in the literature. Through a combination of advanced microstructural characterization techniques and density functional theory (DFT) calculations, we reveal that the symbiotic interaction between topological carbon defects and atomic Fe sites plays a crucial role in enhancing ORR activity and improving zinc-air battery performance.

Single atom catalysts have been recognized as potential catalysts to fabricate electrochemical biosensors, due to their unexpected catalytic selectivity and activity. Here, we designed and fabricated an ultrasensitive dopamine (DA) sensor based on the flower-like MoS₂ embellished with single Ni site catalyst (Ni-MoS₂). The limit of detection could achieve 1 pM in phosphate buffer solution (PBS, pH = 7.4), 1 pM in bovine serum (pH = 7.4), and 100 pM in artificial urine (pH = 6.8). The excellent sensing performance was attributed to the Ni single atom axial anchoring on the Mo atom in the MoS₂ basal plane with the Ni-S₃ structure. Both the experiment and density functional theory (DFT) results certify that this structural feature is more favorable for the adsorption and electron transfer of DA on Ni atoms. The high proportion of Ni active sites on MoS₂ basal plane effectively enhanced the intrinsic electronic conductivity and electrochemical activity toward DA. The successful establishment of this sensor gives a new guide to expand the field of single atom catalyst in the application of biosensors.