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Steven J.T.,MacDiarmid Institute for Advanced Materials and Nanotechnology | Golovko V.B.,MacDiarmid Institute for Advanced Materials and Nanotechnology | Johannessen B.,Australian SynchrotronVIC | Marshall A.T.,MacDiarmid Institute for Advanced Materials and Nanotechnology
Electrochimica Acta

Cyclic voltammetry has been used to assess the electrochemical stability of gold nanoparticle-based electrocatalysts with differing initial particle size distributions in sulphuric acid electrolyte. The electrochemically active surface area (EASA), based on the gold oxide reduction charge, revealed that the electrocatalyst containing gold nanoparticles with an initial number-weighted average diameter of 4.5 nm was stable over 100 voltammetry cycles. Conversely, the electrocatalysts based on 3.1 nm and 2.9 nm gold nanoparticles showed a continuous decrease in the EASA in line with TEM and EXAFS data which confirmed growth of the gold particles during cycling. Importantly, we find no evidence to suggest that the nature of the stabilising ligand used during the gold nanoparticle synthesis, has any effect of the electrochemical stability of gold nanoparticles. When the anodic limit of the cyclic voltammograms was limited to below the gold oxide formation potential, the nanoparticles were stable, confirming that the loss in EASA is primarily related to the dissolution and growth of gold nanoparticles associated with the Au-AuOx redox process. Interestingly, an electrocatalyst initially containing 0.8 nm diameter gold nanoclusters had a surprisingly low EASA (these clusters appear not to exhibit normal Au-AuOx redox behaviour typical for the larger gold nanoparticles), but still showed significant particle growth during the cycling as confirmed by TEM and XPS analysis. © 2015 Elsevier Ltd. All rights reserved. Source

Roberts J.,Australian National University | Gaugliardo P.,University of Western Australia | Farnan I.,University of Cambridge | Zhang M.,University of Cambridge | And 8 more authors.
Journal of Nuclear Materials

Zircons are a well-known candidate waste form for actinides and their radiation damage behaviour has been widely studied by a range of techniques. In this study, well-characterised natural single crystal zircons have been studied using Positron Annihilation Lifetime Spectroscopy (PALS). In some, but not all, of the crystals that had incurred at least half of the alpha-event damage of ∼1019 α/g required to render them structurally amorphous, PALS spectra displayed long lifetimes corresponding to voids of ∼0.5 nm in diameter. The long lifetimes corresponded to expectations from published Small-Angle X-ray Scattering data on similar samples. However, the non-observation by PALS of such voids in some of the heavily damaged samples may reflect large size variations among the voids such that no singular size can be distinguished or. Characterisation of a range of samples was also performed using scanning electron microscopy, optical absorption spectroscopy, Raman scattering and X-ray scattering/diffraction, with the degree of alpha damage being inferred mainly from the Raman technique and X-ray diffraction. The observed void diameters and intensities of the long lifetime components were changed somewhat by annealing at 700 °C; annealing at 1200 °C removed the voids entirely. The voids themselves may derive from He gas bubbles or voids created by the inclusion of small quantities of organic and hydrous matter, notwithstanding the observation that no voidage was evidenced by PALS in two samples containing hydrous and organic matter. Crown Copyright © 2016 Published by Elsevier B.V. All rights reserved. Source

Mellsop S.R.,MacDiarmid Institute for Advanced Materials and Nanotechnology | Gardiner A.,Callaghan Innovation | Johannessen B.,Australian SynchrotronVIC | Marshall A.T.,MacDiarmid Institute for Advanced Materials and Nanotechnology
Electrochimica Acta

The anodic behaviour of a nickel electrode has been investigated in KOH electrolytes below and above the oxygen evolution potential. As the literature reports a wide range of behaviours, initial repetitive cyclic voltammetry in 1 M KOH was compared to 30 wt% KOH (i.e., that used in alkaline water electrolysers) and it was found that a process in addition to the normal α-Ni(OH)2/γ-NiOOH and β-Ni(OH)2/β-NiOOH occurs in the more concentrated electrolyte. It is also confirmed that the initial hydroxide layer formed anodically from metallic nickel is not α-Ni(OH)2, but a layer which is more readily reducible than α-Ni(OH)2. At higher potentials, while in-situ XAS suggested that γ-NiOOH is not transformed to any further phase up to 0.665 V vs HgHgO in 1 M KOH, after extensive OER (at least 40 hrs) in 30 wt% at 50 mA cm-2, an additional phase can be identified by cyclic voltammetry. Overall, during galvanostatic oxygen evolution, the nickel anodes follow an ageing behaviour characterised by a brief activation period, a short period of high activity (i.e., low overpotential) followed by deactivation and eventually stable but poor activity. While no clear evidence was obtained to identify the most active phase for oxygen evolution, it is likely that this is related to β-NiOOH and confined to the very surface of the electrode. © 2015 Elsevier Ltd. Source

Ciccotosto G.D.,University of Melbourne | James S.A.,Australian SynchrotronVIC | James S.A.,CSIRO | Altissimo M.,Elettra - Sincrotrone Trieste | And 7 more authors.

The amyloid precursor protein (APP) gene family includes APP and the amyloid precursor-like proteins, APLP1 and APLP2. These proteins contain metal binding sites for copper, zinc and iron and are known to have physiological roles in modulating the metal homeostasis in brain cells. Here we report the application of X-ray fluorescence microscopy (XFM) to investigate the subcellular distribution patterns of the metal ions Cu, Zn, Fe, and Ca in individual neurons derived from APP and APLP2 knockout mice brains to further define their role in metal homeostasis. These studies add to the growing body of data that the APP family of proteins are metalloproteins that have shared as well as distinct effects on metals. As we continue to delineate the cellular effects of the APP family of proteins it is important to consider how metals are involved in their actions. © the Partner Organisations 2014. Source

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