Ammonia is considered a promising hydrogen carrier due to its high hydrogen density and liquefaction temperature. Considering that the energy efficiency generally decreases as chemical conversion is repeated, it is more efficient to directly use ammonia as a fuel for fuel cells. However, catalysts in direct ammonia fuel cells have the critical issues of sluggish ammonia oxidation reaction (AOR) rate and poisoning of reaction intermediates. In particular, the use of precious metal as cathodic catalysts has been limited due to ammonia crossover and poisoning. In this study, we introduce Fe-based single-atom catalysts with selective activity for the oxygen reduction reaction (ORR) even in the presence of ammonia. As the Fe content increased, the single-atom structure of the catalysts changed into Fe nanoparticles or carbides. Among our Fe–N–C catalysts, FeNC-50 with a Fe loading amount of 0.34 wt% showed the highest ORR performance regardless of the ammonia concentration. In particular, the difference in activity between the catalysts increased as the concentration increased. The FeNC-50 catalyst showed remarkable stability after 1000 cycles. Therefore, we believe that single-atom dispersion is an important factor in the development of stable non-precious catalysts with high activity and inactivity for the ORR and AOR, respectively.

Untargeted metabolomic fingerprinting is a discovery tool for the identification of metabolites associated with the response to dietary and environmental perturbations. Direct analysis in real-time mass spectrometry (DART MS) promises to be a powerful analytical technique for high-throughput metablome analysis of insect. In this study, we used the DART MS technique to find tracers related to the origin of small brown planthopper (Laodelphax striatellus), and conducted a untargeted metabolomic fingerprinting on the wings and exoskeleton in Chinese and domestic collectives. This paper showed that DART MS metabolomic fingerprinting represents a rapid and powerful analytical strategy enabling distinguish of two different origin’s small brown planthoppers by recording metabolomic fingerprints.