RESUMEN
In this work, we introduce composition-tunable core-shell-like PdM@Pt (Mâ¯=â¯Mn and Fe) nanoparticles (NPs) on carbon support (PdM@Pt/C) synthesized by one-pot sonochemical reactions using high-intensity ultrasonic probe (150â¯W, 20â¯kHz, with 13â¯mm solid probe) and investigate their electrocatalytic performance for oxygen reduction reaction (ORR). The core-shell-like structure of the NPs are evidenced by the elemental distribution maps obtained by energy dispersive X-ray spectroscopy equipped on scanning transmission electron microscopy. Based on the characterization data, PdM@Pt NPs were synthesized with variable elemental compositions (Pd49Fe21@Pt30, Pd17Fe31@Pt52, Pd46Mn6@Pt48 and Pd15Mn5@Pt80). All PdM@Pt samples are composed of large (~10â¯nm) and small (~3 nm) NPs, the large ones appear to be aggregates of the smaller ones, and the proportion of the larger NPs increases with the Pd content, which can be explained with the known mechanisms of sonochemical reactions of related systems. Electrochemical analyses on samples show that the ORR mass activity of PdM@Pt/C is 3-fold (normalized by Pt) and 1.7-fold (normalized by platinum group metal (PGM)) higher than those of Pt/C (commercial). All PdM@Pt/C sample show superior durability with the electrochemical surface area (ECSA) change of -4.4-+12.0% and half-wave potential change (ΔE1/2) of 8-14â¯mV after 10â¯k cycles accelerated stress test (AST) to Pt/C with ECSA change of -25.6% and ΔE1/2 of 19â¯mV.
RESUMEN
In this work, we present facile synthesis of amorphous Ni/Fe mixed (oxy)hydroxide (NiFe(H)) nanoparticles (NPs) and their electrocatalytic performance for oxygen evolution reaction (OER) in alkaline media. a-NiFe(H) NPs have received lots of attention as OER electrocatalysts with many desirable properties. By using a simple sonochemical route, we prepared amorphous Ni and Fe-alkoxide (NiFe(A)) NPs whose composition can be controlled in the entire composition range (Ni100-xFex, 0≤x≤1). These samples are composed of extremely small NiFe(A) NPs with Ni and Fe atoms homogeneously distributed. NiFe(A) NPs are readily converted into corresponding electrocatalytically active NiFe(H) NP by a simple electrochemical treatment. Electrochemical analysis data show that the OER activity of amorphous NiFe(H) samples follows the volcano-type trend when plotted against the Fe content. Ni70Fe30(H) sample showed the lowest overpotential of 292mV at 10mAcm-2geo and the lowest Tafel slope of 30.4mVdec-1, outperforming IrOx/C (326mV, 41.7mVdec-1). Our samples are highly durable based on the chronopotentiometry data at the current density of 10mAcm-2geo for 2h which show that Ni70Fe30 sample maintains the steady-state potential, contrary to the time-varying IrOx/C.
RESUMEN
Practical applications require the production and usage of metallic nanocrystals (NCs) in large ensembles. Besides, due to their cluster-bulk solid duality, metallic NCs exhibit a large degree of structural diversity. This poses the question as to what atomic-scale basis is to be used when the structure-function relationship for metallic NCs is to be quantified precisely. We address the question by studying bi-functional Fe core-Pt skin type NCs optimized for practical applications. In particular, the cluster-like Fe core and skin-like Pt surface of the NCs exhibit superparamagnetic properties and a superb catalytic activity for the oxygen reduction reaction, respectively. We determine the atomic-scale structure of the NCs by non-traditional resonant high-energy X-ray diffraction coupled to atomic pair distribution function analysis. Using the experimental structure data we explain the observed magnetic and catalytic behavior of the NCs in a quantitative manner. Thus we demonstrate that NC ensemble-averaged 3D positions of atoms obtained by advanced X-ray scattering techniques are a very proper basis for not only establishing but also quantifying the structure-function relationship for the increasingly complex metallic NCs explored for practical applications.
RESUMEN
The present study showed that ancient parasite eggs, not commonly present in soil samples from medieval Korean tombs, have been found in a very limited number of cases that satisfy certain archaeological requirements. In our paleo-parasitological examination of soil samples from medieval tombs encapsulated by a lime soil mixture barrier (LSMB), parasite eggs were more commonly detected in tombs that contained remains with clothes, hair, or brain tissue, though samples from not all such tombs contained eggs. Nonetheless, there was a close correlation between the preservation of certain types of cultural or human remains and the presence of ancient parasite eggs within medieval Korean LSMB tombs. Such remains, therefore, could be regarded as a strong predictor of well-preserved ancient parasite eggs in soil samples from LSMB tombs.