Exploring highly efficient platinum single-atom (Pt1) catalysts for oxygen reduction reaction (ORR) is desired to greatly reduce the catalysts costs of polymer electrolyte membrane (PEM) fuel cells. Herein, based on a nitrogen-doped active carbon (N-doped Black Pearl, NBP), an atomically dispersed Pt-based electrocatalyst is first prepared via a hydrothermal ethanol reduction method with Pt content of about 5 wt % (Pt1/NBP), and it shows high selectivity for the two-electron oxygen reduction pathway. Through further high-temperature pyrolysis, the coordination environment of these isolated Pt atoms is reconstructed to form uniquely nitrogen-anchored platinum single-atom active sites (Pt1@Pt/NBP) for a highly efficient four-electron oxygen reduction pathway. The obtained Pt1@Pt/NBP catalyst presents excellent ORR performance and stability as well as fast ORR kinetics at a high potential region. As a cathode catalyst of a PEM fuel cell, Pt1@Pt/NBP demonstrates 8.7 times higher mass activity than the commercial Pt/C at a cell voltage of 0.9 V.

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Corrosion of carbon support is one of the most crucial causes of the degradation of polymer electrolyte membrane fuel cells (PEMFCs) utilizing carbon-supported platinum nanoparticles (Pt/C) as a catalyst. To mitigate carbon corrosion, Pt is alloyed with iridium (Ir), which is catalytically active for the oxygen evolution reaction (OER), with various compositions of Pt x Ir y . The carbon-supported Pt x Ir y alloy catalysts (Pt x Ir y /C) show slightly lower initial activity for the oxygen reduction reaction (ORR) than Pt/C. However, the ORR activities of the Pt x Ir y /C catalysts increase with repeating potential cycles from 1.0 to 1.5 V RHE , while Pt/C exhibits a rapid decay in the ORR activity and a mixture of Pt/C and Ir/C (Pt/C + Ir/ C, Pt-to-Ir ratio of 85:15) maintains its initial activity. After 5k potential cycles, the mass activity of Pt 85 Ir 15 was 0.071 A mg PGM −1 , which is significantly higher than that of Pt/C (0.017 A mg PGM −1 ) and Pt/C + Ir/C (0.039 A mg PGM −1 ). These results can be attributed to the atomically distributed Ir in Pt 85 Ir 15 . Clearly, carbon corrosion occurs in Pt/C and in Pt-rich regions of Pt/C + Ir/C, whereas the carbon support in Pt 85 Ir 15 /C is effectively protected from corrosion. As a result, the greatest amount of CO 2 emission is detected as coming from Pt/C, followed by Pt/C + Ir/C and Pt 85 Ir 15 /C. During the potential cycles, high-index Pt facets are formed on the surface of Pt 85 Ir 15 /C, leading to an increase in the ORR activity. When employed as cathode catalysts of a PEMFC, Pt 85 Ir 15 /C exhibits improved durability compared to Pt/C and Pt/C + Ir/C under high-voltage cycles to 1.5 V (5k cycles). This work demonstrates that the atomic distribution of Ir in Pt is an effective strategy for mitigating corrosion of the carbon support and to enhance the durability of PEMFCs exposed to high potentials.

Biocompatible magnetic fluids are applied for medical diagnosis and therapy. In this work, magnetic particles were prepared and then were coated with various 2nd surfactants for obtaining the water-based magnetic fluids by chemical coprecipitation. Toxicity of each fluid sample was estimated using SpragueDawley rats. Finally, the used samples resulted in severe toxic reactions through in vitro, indicating that all samples can not be seen as biocompatible agents or suggesting the possibilities of another effects.1 Introduction Recently, the synthesis of magnetic materials in nanoscale has become a field of intense study due to the novel mesoscopic properties shown by particle dimension located in the transition region between atoms and bulk solids. Based on their unique physical, thermal, and mechanical properties, superparamagnetic nanoparticles offer a high potential for several applications in different areas such as ferrofluids, color imaging, magnetic refrigeration, detoxification of biological fluids, magnetically controlled transport of anti-cancer drugs, magnetic resonance imaging contrast enhancement and magnetic cell separation [1][2][3][4].A difficulty related to the nature of ferrofluids is that the nanoparticles with a large ratio of surfacearea to volume tend to agglomerate in order to reduce their surface energy by strong magnetic dipoledipole attraction between particles. Therefore, one of the main problems in producing stable magnetic fluid is to prevent the agglomeration during synthesis and coating processes [5]. Since ionic magnetic fluids are usually toxic materials, the coated layer using a biological molecule such as citrate would provide some protection against toxicity [6].Thus, the purpose of this work was to investigate the toxicity of each surfactant coated magnetic fluid through intravenous administration in Sprague-Dawley rats.

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