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  1. Here we report on hydride-terminated (HT) electrodeposition of Pt multilayers onto ∼1.6 nm Au nanoparticles (NPs). The results build on our earlier findings regarding electrodeposition of a single monolayer of Pt onto Au NPs and reports relating to HT Pt electrodeposition onto bulk Au. In the latter case, it was found that electrodeposition of Pt from a solution containing PtCl 4 2− can be limited to a single monolayer of Pt atoms if it is immediately followed by adsorption of a monolayer of H atoms. The H-atom capping layer prevents deposition of Pt multilayers. In the present report we are interested in comparing the structure of NPs after multiple HT Pt electrodeposition cycles to the bulk analog. The results indicate that a greater number of HT Pt cycles are required to electrodeposit both a single Pt monolayer and Pt multilayers onto these Au NPs compared to bulk Au. Additionally, detailed structural analysis shows that there are fundamental differences in the structures of the AuPt materials depending on whether they are prepared on Au NPs or bulk Au. The resulting structures have a profound impact on formic acid oxidation electrocatalysis. 
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  2. In this report, density functional theory (DFT) calculations of O and OH binding energies on triatomic surface ensembles of Pd x Ir (100−x) nanoalloys successfully predicted the overall trend in experimental oxygen reduction reaction (ORR) activity as a function of nanoparticle (NP) composition. Specifically, triatomic Pd 3 ensembles were found to possess optimal O and OH binding energies and were predicted to be highly active sites for the ORR, rivaling that of Pt(111). However, DFT calculations suggest that the O binding energy increases at active sites containing Ir, thereby decreasing ORR activity. Pd x Ir (100−x) nanoalloys were synthesized using a microwave-assisted method and their activity towards the ORR was tested using rotating disk voltammetry (RDV). As predicted, the bimetallic electrocatalysts exhibited worse catalytic activity than the Pd-only NPs. The strong qualitative correlation between the theoretical and experimental results demonstrates that the activity of individual active sites on the surface of NPs can serve as a proxy for overall activity. This is a particularly useful strategy for applying DFT calculations to electrocatalysts that are too large for true first-principle analysis. 
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  3. A microwave assisted method was used to synthesize RhAu nanoparticles (NPs). Characterization, based upon transmission electron microscopy (TEM), energy dispersive spectroscopy, and powder X-ray diffraction, provided the evidence of monomodal alloy NPs with a mean size distribution between 3 and 5 nm, depending upon the composition. Extended X-ray adsorption fine-structure spectroscopy (EXAFS) also showed evidence of alloying, but the coordination numbers of Rh and Au indicated significant segregation between the metals. More problematic were the low coordination numbers for Rh; values of ca. 9 indicate NPs smaller than 2 nm, significantly smaller than those observed with TEM. Additionally, no single-particle structural models were able to reproduce the experimental EXAFS data. Resolution of this discrepancy was achieved with high resolution aberration corrected scanning TEM imaging which showed the presence of ultra-small (<2 nm) pure Rh clusters and larger (∼3–5 nm) segregated particles with Au-rich cores and Rh-decorated shells. A heterogeneous model with a mixture of ultrasmall pure Rh clusters and larger segregated Rh/Au NPs was able to explain the experimental measurements of the NPs over the range of compositions measured. The combination of density functional theory, EXAFS, and TEM allowed us to quantify the heterogeneity in the RhAu NPs. It was only through this combination of theoretical and experimental techniques that resulted in a bimodal distribution of particle sizes that was able to explain all of the experimental characterization data. 
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  4. Abstract

    Here we show that just three electrochemical scans to modest positive potentials result in substantial growth of 1–2 nm Au dendrimer‐encapsulated nanoparticles (DENs). We examined two sizes of Au DENs, denoted as G6‐NH2(Au147) and G6‐NH2(Au55), where G6‐NH2represents a sixth‐generation, amine‐terminated, poly(amidoamine) dendrimer and the subscripts, 147 and 55, represent the average number of atoms in each size of DENs.Ex situtransmission electron microscopy (TEM) andin situX‐ray absorption spectroscopy (XAS) results indicate that G6‐NH2(Au55) DENs grow to the same size as the G6‐NH2(Au147) DENs following these scans. Importantly, this growth occurs prior to the onset of detectable faradaic Au oxidation or reduction current. The observed growth in the size of the DENs directly correlates to changes in the electrocatalytic ORR activity. The key point is that after just three positive scans the G6‐NH2(Au147) and G6‐NH2(Au55) DENs are essentially indistinguishable in terms of both physical and electrocatalytic properties.

     
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