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The composition and structure of multimetallic nanostructures can be tailored to enhance electrocatalytic properties. This work reports a seed-mediated synthesis of novel multimetallic dendritic core-frame and frame nanostructures with a rhombic dodecahedral shape for enhanced methanol oxidation reaction (MOR). The synthesis involves insitu formation of Cu seeds and the subsequent selective deposition of Pt and Ru on the edges and vertices of the Cu seeds to generate CuPt and CuPtRu dendritic core-frame nanostructures. The core-frame nanostructures undergo a post acetic acid etching process to form the frame nanostructures. While transmission electron microscopy reveals the morphology and elemental distribution of the nanostructures, X-ray diffraction patterns confirm the alloy compositions of dendritic frames for both the core-frame and frame nanostructures. Compared to the bimetallic CuPt nanostructures, the trimetallic CuPtRu nanostructures lower the onset potential and completely suppress the peak current in the reverse scan for MOR. The CuPtRu alloyed frame nanostructures are the best to prevent Ru leaching compared to the CuPtRu core-frame nanostructures and PtRu catalysts. X-ray photoelectron spectroscopy reveals that all three elements become more electron rich in the frame nanostructures. Further refining the composition ratio of the CuPtRu alloyed dendritic frame nanostructures can lead to more efficient catalysts at a lower cost for MOR.

Disentangling the primary order parameter from secondary order parameters in phase transitions is critical to the interpretation of the transition mechanisms in strongly correlated systems and quantum materials. Here we present a study of structural phase transition pathways in superionic Cu2S nanocrystals that exhibit intriguing properties. Utilizing ultrafast electron diffraction techniques sensitive in both momentum-space and the time-domain, we distinguish the dynamics of crystal symmetry breaking and lattice expansion in this system. We are able to follow the transient states along the transition pathway and so observe the dynamics of both the primary and secondary order parameters. Based on these observations we argue that the mechanism of the structural phase transition in Cu2S is dominated by the electron-phonon coupling. This mechanism advances the understanding from previous results where the focus was solely on dynamic observations of the lattice expansion.

1D metal nanostructures exhibit unique properties due to their high aspect ratio for use in many applications including electrocatalysis. This work develops a solution-based approach to 1D multimetal nanostructures with tunable surface structures by combining the two processes of coreduction and galvanic replacement. In this approach, noble metals of Pt and Ru are reduced in the presence of in situ formed Cu seeds. At high concentrations of noble metal precursors, coreduction dominates over galvanic replacement, leading to overgrowth of ultrafine, particulate, or branched structures on the surface of the 1D nanostructures. The surface roughness and composition can be tuned by varying the concentrations of noble metal precursors. The electrochemical reactivity is not only affected by the surface roughness (i.e., the size of particulates and the level of branches) but also the surface composition (i.e., the amount of Pt content). For trimetallic nanostructures, the alloy composition prevents the dissolution of Ru thereby improving electrocatalytic stability of the catalyst under acidic conditions. The structure-property study reveals that the surface structure plays an important role in tailoring the electrocatalytic property of a catalyst.

The optimal functionalities of materials often appear at phase transitions involving simultaneous changes in the electronic structure and the symmetry of the underlying lattice. It is experimentally challenging to disentangle which of the two effects--electronic or structural--is the driving force for the phase transition and to use the mechanism to control material properties. Here we report the concurrent pumping and probing of Cu2S nanoplates using an electron beam to directly manipulate the transition between two phases with distinctly different crystal symmetries and charge-carrier concentrations, and show that the transition is the result of charge generation for one phase and charge depletion for the other. We demonstrate that this manipulation is fully reversible and nonthermal in nature. Our observations reveal a phase-transition pathway in materials, where electron-induced changes in the electronic structure can lead to a macroscopic reconstruction of the crystal structure.

We developed a quantitative model that agrees with, and provides simple parameters to quantify, experimental measurements of AgNPs' antimicrobial activity.

Direct methanol fuel cells commonly utilize platinum based catalysts due to their efficiency for methanol oxidation (MOR). Platinum based electrocatalysts are limited by intermediates adsorbing onto the electrocatalyst’s surface.1 Methanol oxidation forms multiple intermediate species, which are integral in generating electrons that drive the fuel cell.2 The production of intermediate species can also slow down reaction kinetics, while specific intermediate species can strongly adsorb onto active sites along the platinum catalyst surface reducing the number of MOR reactive sites. In order to remove the adsorbed intermediates, the MOR onset potential will shift to a more oxidizing potential.1These limitations can be addressed by developing a durable electrocatalyst that resists CO poisoning, maintains efficiency for MOR, and reduces the onset potential of methanol oxidation. An electrocatalyst comprised of nanomaterials could address some of these limitations, due to their synthetically tunable properties. Nanomaterials can be tailored to possess the ideal composition, morphology, and surface roughness for the catalysis of specific reactions. Previous studies have shown that Pt-based nanomaterials are efficient electrocatalysts, and their activity can be attributed to energetically favorable surface facets, as well as synergistic properties of alloys, specifically electronic and geometric effects.3 Geometric effects allow for the contraction or expansion of the nanomaterial’s crystal lattice, altering its electrochemical activity for a specific fuel.4 Electronic effects occur when the center d-band shifts, weakening the bond to the adsorbed species. In the case of MOR, the oxidation of CO would become more energetically favorable.1 These effects improve the resistance of intermediate poisoning, as well as the activity of the electrocatalyst by freeing more reactive sites. These effects can also influence the activity of pair sites in platinum alloyed nanomaterials, through the bifunctional mechanism.1 , 3 , 5 Previous work by our group investigated the effect of anisotropic alloyed nanostructures electrochemical activity, which demonstrated that the platinum-copper nanodendrites can enhance the MOR activity, while maintaining the dendritic morphology of the nanostructures.1 Current research focuses on the development of multimetallic nanostructures with various morphologies, surface roughness, as well as investigating each nanomaterial’s electrocatalytic activity. Multimetallic nanostructures are formed by first synthesizing copper nanomaterials. Then platinum and ruthenium precursor salts can alloy and co-reduce onto the vertices and edges of the copper nanomaterials, through galvanic replacement and co-reduction mechanisms. The morphology, porosity, surface roughness, and composition of these ruthenium-platinum-copper nanomaterials can be synthetically tailored. Platinum and ruthenium were chosen as secondary alloying metals with copper due to their binding energy for species such as –CO, -OH.6 During the synthetic process pair sites between Pt, Cu, and Ru will form, which could improve resistance towards intermediate poisoning and activity for MOR. The activity of these supportless electrocatalysts will be evaluated by cyclic voltammetry and chronoamperometry. The electrochemical surface area, the charging double layer capacitance, surface diffusion, the efficiency for MOR, and the resistance for CO for each electrocatalyst will be evaluated. Additionally, the morphological and electrochemical durability of each multimetallic nanomaterial in electrolyte and analyte will also be studied in this work. As previously discussed the pair site can affect the electrocatalytic activity for MOR; this work will also study the influence of the nanomaterial's copper core on the electrocatalytic properties. 1. Chen, A.; Holt-Hindle, P., Platinum-Based Nanostructured Materials: Synthesis, Properties, and Applications. Chemical Reviews 2010, 110(6), 3767-3804. 2. Cohen, J. L.; Volpe, D. J.; Abruna, H. D., Electrochemical determination of activation energies for methanol oxidation on polycrystalline platinum in acidic and alkaline electrolytes. Physical Chemistry Chemical Physics 2007, 9(1), 49-77. 3. Lee, H.-Y.; Vogel, W.; Chu, P. P.-J., Nanostructure and Surface Composition of Pt and Ru Binary Catalysts on Polyaniline-Functionalized Carbon Nanotubes. Langmuir 2011, 27(23), 14654-14661. 4. Wang, J. X.; Ma, C.; Choi, Y.; Su, D.; Zhu, Y.; Liu, P.; Si, R.; Vukmirovic, M. B.; Zhang, Y.; Adzic, R. R., Kirkendall Effect and Lattice Contraction in Nanocatalysts: A New Strategy to Enhance Sustainable Activity. Journal of the American Chemical Society 2011, 133(34), 13551-13557. 5. Sun, X.; Li, D.; Ding, Y.; Zhu, W.; Guo, S.; Wang, Z. L.; Sun, S., Core/Shell Au/CuPt Nanoparticles and Their Dual Electrocatalysis for Both Reduction and Oxidation Reactions. Journal of the American Chemical Society 2014, 136(15), 5745-5749. 6. Rossmeisl, J.; Ferrin, P.; Tritsaris, G. A.; Nilekar, A. U.; Koh, S.; Bae, S. E.; Brankovic, S. R.; Strasser, P.; Mavrikakis, M., Bifunctional anode catalysts for direct methanol fuel cells. Energy & Environmental Science 2012, 5 (8), 8335-8342.

The effects of using polydopamine (PDA) coated Cu nanoparticles (PDA-Cu) as a filler in the polytetrafluoroethylene (PTFE) topcoat of a PDA/PTFE dual-layer coating are investigated, where the PDA is used as an adhesive basecoat. Tribological tests show that the addition of PDA-Cu in PTFE increases the wear life of PDA/PTFE by a factor of two, approximately three orders of magnitude greater than that of pure PTFE without a PDA basecoat. This increase in wear life is achieved without compromising the low coefficient of friction characteristic of pure PTFE. Scratch tests show that the PDA-Cu filler improves adhesion between the PTFE and the PDA, preventing large scale delamination and also increases the toughness of the coating, preventing ruptures at lower loads.

Platinum materials are traditionally utilized as the standard electrocatalysts in direct methanol fuel cells; however, platinum is hindered by CO poisoning, which is an intermediate of methanol oxidation.1 CO adsorption to platinum active sites causes slow kinetics for methanol oxidation (MOR), and requires higher onset potential for the removal of adsorbed CO and commencement of methanol oxidation.1 Bimetallic Pt-based nanomaterials can function as efficient electrocatalysts due to the synergistic properties of alloys, specifically electronic and geometric effects.2 Electronic effects occur when the center d-band is shifted upwards, weakening the bond to the adsorbed CO, allowing for easier oxidation of CO.1 The geometric effects allow for the contraction or expansion of their crystal lattice, resulting in the alternation of the electrochemical activity for a specific fuel.3 When platinum is alloyed with either copper or ruthenium, the electrocatalysts can become more tolerant to CO adsorption.2 , 4 In addition, the bifunctional alloys can enhance electrocatalytic activity for MOR. An oxygenated species (-OH) favorably adsorb onto the additional metal, aids in the oxidation of CO adsorbed on platinum.1 Anisotropic nanostructures can increase the electrochemical activity while maintaining the stability of catalysts. Additionally, nanomaterials possess tunable surface area, morphologies, and surface facets that enable the formation of a catalyst with enhanced electrocatalytic activity.5 , 6 We have demonstrated that the platinum-copper nanodendrites can enhance the MOR activity and maintain the dendritic morphology of the nanostructures.7 In this work, we synthesize binary and ternary metallic nanotubes and study their activity for MOR. Bimetallic nanostructures are formed first by alloying platinum precursor salts with copper nanowires through the galvanic replacement and co-reduction mechanisms. This process forms hollow platinum-copper nanotubes with controllable surface roughness. To further improve the activity for MOR, we alloy ruthenium into platinum-copper nanostructures. The morphology, surface roughness, and composition of these ruthenium-platinum-copper nanotubes can be synthetically tuned by controlling the precursor ratio, reaction time, and reaction temperature. The electrochemical activity for MOR will be evaluated by cyclic voltammetry and chronoamperometry to characterize the electrochemical surface area, the efficiency for MOR, the tolerance for CO, and the stability of the electrocatalysts in acidic media. The enhanced activity of these multimetallic nanostructures as supportless electrocatalysts for MOR will be discussed. 1. Chen, A.; Holt-Hindle, P., Platinum-Based Nanostructured Materials: Synthesis, Properties, and Applications. Chemical Reviews 2010, 110 (6), 3767-3804. 2. Lee, H.-Y.; Vogel, W.; Chu, P. P.-J., Nanostructure and Surface Composition of Pt and Ru Binary Catalysts on Polyaniline-Functionalized Carbon Nanotubes. Langmuir 2011, 27 (23), 14654-14661. 3. Wang, J. X.; Ma, C.; Choi, Y.; Su, D.; Zhu, Y.; Liu, P.; Si, R.; Vukmirovic, M. B.; Zhang, Y.; Adzic, R. R., Kirkendall Effect and Lattice Contraction in Nanocatalysts: A New Strategy to Enhance Sustainable Activity. Journal of the American Chemical Society 2011, 133 (34), 13551-13557. 4. Sun, X.; Li, D.; Ding, Y.; Zhu, W.; Guo, S.; Wang, Z. L.; Sun, S., Core/Shell Au/CuPt Nanoparticles and Their Dual Electrocatalysis for Both Reduction and Oxidation Reactions. Journal of the American Chemical Society 2014, 136 (15), 5745-5749. 5. Koenigsmann, C.; Zhou, W.-p.; Adzic, R. R.; Sutter, E.; Wong, S. S., Size-Dependent Enhancement of Electrocatalytic Performance in Relatively Defect-Free, Processed Ultrathin Platinum Nanowires. Nano Letters 2010, 10 (8), 2806-2811. 6. Li, M.; Liu, P.; Adzic, R. R., Platinum Monolayer Electrocatalysts for Anodic Oxidation of Alcohols. The Journal of Physical Chemistry Letters 2012, 3 (23), 3480-3485. 7. Taylor, E.; Chen, S.; Tao, J.; Wu, L.; Zhu, Y.; Chen, J., Synthesis of Pt–Cu Nanodendrites through Controlled Reduction Kinetics for Enhanced Methanol Electro-Oxidation. ChemSusChem 2013, 6 (10), 1863-1867.