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Research was conducted to examine the elastic field and the interaction energy associated with surface steps and adatoms. A harmonic model is proposed that presents a number of considerable advantages when compared to continuum models of Embedded Atom Method (EAM) simulations. Results are in good agreement with atomic EAM simulation results as well as the far-field predictions of continuum elastic theory.

Historically, there have been two general approaches for understanding alloy passivation behavior. One involves study of the composition and crystal structure of the passive film and the other is concerned with how the composition and structure of the metallic alloy dictates the formation of the film. Herein we describe a recently developed theory based on a conjecture of Sieradzki and Newman connected to percolation theory and use the theory to model the passivation behavior of a series of Cu-Rh alloys. Our results are in quantitative agreement with the predictions of this theory. We discuss how the theory elucidates the important role of short-range order in understanding how composition affects the details of the passivation process. [ABSTRACT FROM AUTHOR]

Several thermodynamic analyses are conducted to explain the construction and the electrochemical stability as exhibited by the various elemental metal nanoparticles. The case of Pt is taken to demonstrate the significance and validity of the method.

The electrochemical scanning tunneling microscopy is utilized to directly examine the stability of individual Pt nanoparticles as a function of applied potential. The results obtained have significant implications for understanding the stability of Pt and Pt alloy catalysts in fuel cell architectures, and for the stability of nanoparticles in general.

We report on a study of morphology evolution following de-lithiation of Li-Pb alloys, produced by the electrochemical lithiation of Pb particulate and sheet electrodes. Electrochemical titration and time of flight measurements were performed in order to determine the intrinsic diffusivity of Li, D̄Li, as a function of alloy composition, which ranged from 10-12-10-10 cm²s-1. Morphology evolution was studied under conditions of galvanostatic and potentiostatic dealloying. For the particulate electrodes, we observed dealloyed morphologies corresponding to Kirkendall voids, negative dendrites, void nodules and conventional bicontinuous nanoporous structures. In the case of Pb sheets, similar dealloyed morphologies were obtained under galvanostatic dealloying conditions, however, in the case of potentiostatic dealloying, we did not observe the formation of large volume bicontinuous nanoporous structures. For Pb sheets lithiated to a composition corresponding to the Li8Pb3 phase and galvanostatically dealloyed at current densities ~1mAcm-2, voltage oscillations were observed with periods of 70-90 s and amplitudes ranging from 20-130 mV. Current oscillations were also observed for potentiostatic dealloying at 1 V vs Li+/Li. The possible mechanism of these oscillations is discussed and attributed to a salt film precipitation and lift-off process. [ABSTRACT FROM AUTHOR]

Dealloying under conditions of high homologous temperature, TH, (or high intrinsic diffusivity of the more electrochemically reactive component) is considerably more complicated than at low TH since solid-state mass transport is available to support this process. At low TH the only mechanism available for dealloying a solid is percolation dissolution, which results in a bicontinuous solid-void morphology for which nanoporous gold serves as the prototypical example. At high TH, there is a rich set of morphologies that can evolve depending on alloy composition and the imposed electrochemical conditions, including negative or void dendrites, Kirkendall voids and bi-continuous porous structures. We report on a study of morphology evolution upon delithiation of Li-Sn alloys, produced by the electrochemical lithiation of Sn sheets. Electrochemical titration and time of flight measurements were performed in order to determine the intrinsic diffusivity of Li, ...Li, as a function of alloy composition, which ranged from ~5 x 10-8 - 4 x 10-12 cm²s-1. The activation energy for ...Li was measured in the temperature range 30-140°C and found to be 37.4, 37.9 and 22.5 kJ/mole, respectively for the phases Li2Sn5, LiSn and Li7Sn3. Morphology evolution was studied under conditions of fixed dealloying potential and fixed current density and our results are summarized by the introduction of dealloying morphology diagrams that reveal the electrochemical conditions for the evolution of the various morphologies. [ABSTRACT FROM AUTHOR]