Unlike the well-defined long-range order that characterizes crystalline metals, the atomic arrangements in amorphous alloys remain mysterious at present. Despite intense research activity on metallic glasses and relentless pursuit of their structural description, the details of how the atoms are packed in amorphous metals are generally far less understood than for the case of network-forming glasses. Here we use a combination of state-of-the-art experimental and computational techniques to resolve the atomic-level structure of amorphous alloys. By analysing a range of model binary systems that involve different chemistry and atomic size ratios, we elucidate the different types of short-range order as well as the nature of the medium-range order. Our findings provide a reality check for the atomic structural models proposed over the years, and have implications for understanding the nature, forming ability and properties of metallic glasses.

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Pyrolyzed transition metal based porphyrins present an attractive alternative to state of the art Pt-based electrocatalysts for fuel cell applications based on their comparatively low cost. Unfortunately, the large array of precursors and synthetic strategies has led to considerable ambiguity regarding the specific structure/ property relationships that give rise to their activity for oxygen reduction. Specifically, considerable debate exists in actual chemical structure of the pyrolyzed reaction centers, and their relationship to membranedamaging peroxide yield. In this manuscript a comprehensive electrochemical and spectroscopic study of pyrolyzed CoTMPP produced via a self-templating process is presented. The resulting electrocatalysts are not carbon-supported, but are highly porous self-supported pyropolymers. Rotating ring disk electrode measurements showed that the materials pyrolyzed at 700 °C exhibited the highest performance, whereas pyrolysis at 800 °C resulted in a significant increase in the peroxide yield. X-ray photoelectron spectroscopy and Co L and K edge extended X-ray absorption fine structure (EXAFS) studies confirm that the majority of the Co-N 4 active site has broken down to Co-N 2 at 800 °C. Application of ∆µ analysis (an X-ray absorption near-edge structure difference technique) to the in situ Co K edge EXAFS data allowed for direct spectroscopic observation of the geometry of O ads on the pyropolymer active sites. The specific geometrical adsorption of molecular oxygen with respect to the plane of the Co-N x moieties highly influences the oxygen reduction reaction pathway. The application of the ∆µ technique to other transition metal based macrocycle electrocatalyst systems is expected to provide similarly detailed information.

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We have characterized the icosahedral short-range order in amorphous solids using local environment probes. Such topological local order is pronounced even in an amorphous alloy that does not form quasicrystalline phases upon crystallization, as demonstrated by the extended x-ray absorption fine structure and x-ray absorption near-edge structure of a Ni-Ag amorphous alloy analyzed through reverse Monte Carlo simulations.

Self-ordered, highly oriented arrays of titanium-niobium-zirconium mixed oxide nanotube films were fabricated by the anodization of Ti(35)Nb(5)Zr alloy in aqueous and formamide electrolytes containing NH(4)F at room temperature. The nanostructure topology was found to depend on the nature of the electrolyte and the applied voltage. Our results demonstrate the possibility to grow mixed oxide nanotube array films possessing several-micrometer-thick layers by a simple and straightforward electrochemical route. The fabricated Ti-Nb-Zr-O nanotubes showed a ∼17.5% increase in the photoelectrochemical water oxidation efficiency as compared to that measured for pure TiO(2) nanotubes under UV illumination (100 mW/cm(2), 320-400 nm, 1 M KOH). This enhancement could be related to a combination of the effect of the thin wall of the fabricated Ti-Nb-Zr-O nanotubes (10 ± 2 nm) and the formation of Zr oxide and Nb oxide layers on the nanotube surface, which seems to slow down the electron-hole recombination in a way similar to that reported for Grätzel solar cells.

Simulations of platinum oxidation in literature have yet to fully replicate an experimental cyclic voltammogram. In this manuscript a mechanism for platinum oxidation is proposed based upon the results of in operando X-ray absorption spectroscopy, where it was found that PtO2 is present at longer hold times. A new method to quantify extended X-ray absorption fine structure data is presented, and the extent of oxidation is directly compared to electrochemical data. This comparison indicated that PtO2 was formed at the expense of an initial oxide species. From previous literature studies it can be concluded that the rate of platinum oxidation is not a function of only potential and coverage. To that end, the concept of a heterogeneous oxide layer was introduced into the model, whereby place-exchanged PtO2 structures of varying energy states are formed through a single transition state. This treatment allowed, for the first time, the simulation of the correct current-potential behavior at varying scan rates and upper potential limits.

An unresolved question for the layered oxides is: what is the optimum value of y in the formula LiNi y Mn y Co 1-2y O 2 for energy storage at moderate reaction rates? Here we report a systematic study of the specific capacity, rate capability and cycle life of Li x-Ni y Mn y Co 1-2y O 2 (y ¼ 0.5, 0.45, 0.4, and 0.333). The voltage of the Li/y ¼ 0.333 couple crosses over those of lower cobalt content for x < 0.55, as the Co redox begins to get involved. This early involvement of cobalt, rather than just Ni, leads to a slightly smaller specific capacity for y ¼ 0.333 than for LiNi y Mn y Co 1-2y O 2 with y > 0.333 when charging above 4 V. Overall the y ¼ 0.4 material has the optimum properties, having the highest theoretical capacity, less of the expensive cobalt and yet rate capabilities and capacity retention comparable to the y ¼ 0.333 material.