Owing to the unique coordination environment and high atom utilization efficiency, single atom catalysts have been considered as an ideal artificial enzyme to mimic natural enzymes. Herein, single-atom Fe nanozyme anchored on N-doped Ti₃C₂T_x (Fe SA/N-Ti₃C₂T_x) with asymmetrically coordinated Fe-N₁C₂ configuration is synthesized by vacancy capture and heteroatom doping strategy, which exhibits excellent peroxidase-like activity. Based on the results of peroxidase catalytic kinetics and X-ray adsorption fine spectroscopy, the Fe-N₁C₂ active sites in Fe SA/N-Ti₃C₂T_x are responsible for the excellent performance. Furthermore, the developed Fe SA/N-Ti₃C₂T_x can be employed to quantitative detection of melatonin (MT), which shows a wide linear detection range (0.01–100 μM) and an excellent detection limit (7.3 nM) in buffer, 0.01–100 μM and 7.8 nM in serum samples. Our work proves that MXene-based single atoms can be promising nanozyme in the field of bioassays.

The atomic-level interfacial regulation of single metal sites through heteroatom doping can significantly improve the characteristics of the catalyst and obtain surprising activity. Herein, nickel single-site catalysts (SSCs) with dual-coordinated phosphorus and nitrogen atoms were developed and confirmed (denoted as Ni-P_xN_y, x = 1, 2 and y = 3, 2). In CO₂ reduction reaction (CO₂RR), the CO current density on Ni-P_xN_y was significantly higher than that of Ni-N₄ catalyst without phosphorus modification. Besides, Ni-P₁N₃ performed the highest CO Faradaic efficiency (FE_CO) of 85.0%–98.0% over a wide potential range of −0.65 to −0.95 V (vs. the reversible hydrogen electrode (RHE)). Experimental and theoretical results revealed that the asymmetric Ni-P₁N₃ site was beneficial to CO₂ intermediate adsorption/desorption, thereby accelerating the reaction kinetics and boosting CO₂RR activity. This work provides an effective method for preparing well-defined dual-coordinated SSCs to improve catalytic performance, targetting to CO₂RR applications.

The depletion of energy and increasing environmental pressure have become one of the main challenges in the world today. Synthetic high-efficiency catalysts bring hope for efficient conversion of energy and effective treatment of pollutants, especially, single-atom catalysts (SACs) are promising candidates. Herein, we comprehensively summarizes the atomic diffusion strategy, which is considered as an effective method to prepare a series of SACs. According to the different diffusion forms of the precursors, we review the synthesis pathways of SACs from three aspects: gas diffusion, solid diffusion and liquid diffusion. The gaseous diffusion method mainly discusses atomic layer deposition (ALD) and chemical vapor deposition (CVD), both of which carry out gas phase mass transfer at high temperatures. The solid-state diffusion method can be divided into nanoparticle transformation into single atoms and solid atom migration. Liquid diffusion mainly describes the electrochemical method and the molten salt method. We hope this review can trigger the rational design of SACs.