The finding of new metal alloyed nanocrystals (NCs) with high catalytic activity and low cost to replace PtRu NCs is a critical step toward the commercialization of fuel cells. In this work, a simple cation replacement reaction was utilized to synthesize a new type of ternary Fe(1-x)PtRu(x) NCs from binary FePt NCs. The detailed structural transformation from binary FePt NCs to ternary Fe(1-x)PtRu(x) NCs was analyzed by X-ray absorption spectroscopy (XAS). Ternary Fe(35)Pt(40)Ru(25), Fe(31)Pt(40)Ru(29), and Fe(17)Pt(40)Ru(43) NCs exhibit superior catalytic ability to withstand CO poisoning in methanol oxidation reaction (MOR) than do binary NCs (FePt and J-M PtRu). Also, the Fe(31)Pt(40)Ru(29) NCs had the highest alloying extent and the lowest onset potential among the ternary NCs. Furthermore, the origin for the superior CO resistance of ternary Fe(1-x)PtRu(x) NCs was investigated by determining the adsorption energy of CO on the NCs' surfaces and the charge transfer from Fe/Ru to Pt using a simulation based on density functional theory. The simulation results suggested that by introducing a new metal into binary PtRu/PtFe NCs, the anti-CO poisoning ability of ternary Fe(1-x)PtRu(x) NCs was greatly enhanced because the bonding of CO-Pt on the NCs' surface was weakened. Overall, our experimental and simulation results have indicated a simple route for the discovery of new metal alloyed catalysts with superior anti-CO poisoning ability and low usage of Pt and Ru for fuel cell applications.
Cadmium selenide is a II−VI semiconductor model system known for its nanoparticle preparation, growth mechanism, luminescence properties, and quantum confinement studies. For the past 2 decades, various thermodynamically stable "magic-size nanoclusters (MSCs)" of CdSe have been observed, isolated, and theoretically calculated. Nevertheless, none of the proposed structures were experimentally confirmed due to the small crystal domains beyond the diffraction limit. With a combination of nondestructive SAXS, WAXS, XRD, XPS, EXAFS, and MAS NMR techniques, we were able to verify the phase transformation, shape, size dimension, local bonding, and chemical environments of (CdSe) 13 nanoclusters, which are indicative of a paired cluster model. These experimental results are consistent with the size, shape, bond lengths, dipole moment, and charge densities of the proposed "paired-tubular geometry" predicted by computational approaches. In this article, we revisit the formation pathway of the mysterious (CdSe) 13 nanoclusters and propose a paired cluster structure model for better understanding of II−VI semiconductor nanoclusters.
Well-dispersed, highly stable PtRu nanoparticles of ca. 2-3 nm on carbon mesoporous materials (PtRu-CMMs) were synthesized directly using SBA-15 mesoporous silica as the template, furfuryl alcohol and trimethylbenzene as the primary carbon source, and platinum and ruthenium acetylacetonates as the cofeeding metal and carbon precursors. Results obtained from X-ray diffraction and X-ray photoelectron spectroscopy show that the Pt metal in the PtRu-CMMs was present in the form of a face-centered cubic (fcc) crystalline structure and the alloyed PtRu nanoparticles were composed mainly of Ru oxides, Ru(0), and Pt(0) metals. Further studies by X-ray absorption spectroscopy confirmed that a highly alloyed state of the PtRu nanoparticles is responsible for the superior electrocatalytic performance observed for the PtRu-CMMs, as compared to typical commercial electrocatalysts. The Pt 50 Ru 50 -CMM sample was found to possess the best electrocatalytic performance and long-term durability and should appeal to direct methanol fuel cell applications as anodic electrodecatalyst.
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