Browsing by Author "Marshall, AT"

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    Electrochemical CO2 reduction on Au cluster-based electrodes: investigating the role of nafion ionomer
    (The Electrochemical Society, 2023-07-25) Sharma, SK; Johannessen, B; Golovko, VB; Marshall, AT
    The performance of electrocatalytic CO2 reduction (CO2RR) depends not only on the catalytic material but also on the neighbouring chemical environment around the active sites. The surrounding local environment can perturb the electronic properties of active sites and alter the adsorption/desorption behaviour of reactant/intermediate/product, thus changing CO2RR characteristics. Herein, we studied electrochemical reduction of CO2 onto supported atomically precise [Au9(PPh3)8](NO3)3 clusters and observed an unusual increase in catalytic activity over time. Additionally, electrochemical activation of the electrodes by applying a more negative potential was found to improve activity of the electrode. Investigations using UV–vis and X-ray absorption spectroscopy revealed that these observations may be attributed to the interaction of the Nafion ionomer with the catalytic Au9 clusters. These interactions may cause partial blocking of the Au9 active sites, and the prolonged application of negative potentials leads to favourable interface reconstructions. In addition, a method was developed to minimise the interaction between the Au9 clusters and Nafion ionomer by first depositing a layer of carbon black followed by dropcasting the active catalyst. Our study highlights that polymeric binders modulate the electronic properties of the electrocatalysts, which can change the product distribution during CO2 electrolysis. © 2023 The Author(s). Published on behalf of The Electrochemical Society by IOP Publishing Limited.
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    Electron and ion microprobe analysis of calcium distribution and transport in coral tissues
    (Company of Biologists, 2007-07-15) Marshall, AT; Clode, PL; Russell, RA; Prince, KE; Stern, R
    It is shown by x-ray microanalysis that a gradient of total intracellular Ca concentration exists from the outer oral ectoderm to the inner skeletogenic calicoblastic ectoderm in the coral Galaxea fascicularis. This suggests an increase in intracellular Ca stores in relation to calcification. Furthermore, Ca concentration in the fluid-filled space of the extrathecal coelenteron is approximately twice as high as in the surrounding seawater and higher than in the mucus-containing seawater layer on the exterior of the oral ectoderm. This is indicative of active Ca2+ transport across the oral epithelium. Polyps were incubated in artificial seawater in which all 40Ca was replaced by 44Ca. Imaging Ca2+ transport across the epithelia by secondary ion mass spectroscopy (SIMS) using 44Ca as a tracer showed that Ca2+ rapidly entered the cells of the oral epithelium and that 44Ca reached higher concentrations in the mesogloea and extrathecal coelenteron than in the external seawater layer. Very little Ca2+ was exchanged in the mucocytes, cnidocytes or zooxanthellae. These observations again suggest that Ca2+ transport is active and transcellular and also indicate a hitherto unsuspected role in Ca2+ transport for the mesogloea. © 2007, Company of Biologists
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    Influence of carbon support on the pyrolysis of cobalt phthalocyanine for the efficient electroreduction of CO2
    (American Chemical Society, 2022-11-14) Hamonnet, J; Bennington, MS; Johannessen, B; Hamilton, JL; Brooksby, PA; Brooker, S; Golovko, VB; Marshall, AT
    Understanding the nature of the reactive sites of CO2reduction catalysts is crucial to developing efficient and selective materials to help mitigate the greenhouse effect. In this research, materials based on cobalt phthalocyanine supported by carbon black and pyrolyzed at various temperatures under argon are fabricated and tested for CO2electroreduction. The results show that the high reactivity of the catalysts for the electroreduction of CO2to CO is maintained for materials prepared at temperatures up to 700 °C, with CO Faradaic efficiencies of >85% and CO current densities consistently at >40 mA cm-2at -0.86 V vs RHE. The materials annealed up to 900 °C are also remarkably active, with CO Faradaic efficiencies of >40% and CO current densities of >12 mA cm-2. The combination of X-ray diffraction, infrared and Raman spectroscopies, and X-ray absorption analysis show that the annealed materials exhibit chemical structures drastically different from those of the original CoPC and unsupported pyrolyzed catalyst while highlighting the role of the carbon black support in the formation of active species. These results give crucial insight into the reactive structure of CoPC and open the way for the development of pyrolyzed Co-N4macrocycles as a new class of materials efficient for the electroreduction of CO2,. © 2022 American Chemical Society.
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    Multiple metal accumulation within a manganese-specific genus
    (Botanical Society of America, 2013-04) Fernando, DR; Marshall, AT; Forster, PI; Hoebee, SE; Siegele, R
    Premise of the study: Plants that strongly accumulate metals may be practically beneficial, and also serve as novel resources for increasing fundamental understanding of plant biology. Australian Gossia (Myrtaceae) species are delineated by a conspicuous affinity for the heavy metal manganese (Mn), which is a micronutrient crucial to photosynthesis. This genus includes several Mn hyperaccumulators such as G. bidwillii. Unusually, in G. bidwillii foliar Mn is most highly concentrated in photosynthetic cells, an observation thus far restricted to foliar-Mn accumulation in Mn hyperaccumulators. Recent discovery that several of these Gossia species accumulate other metals in addition to Mn will enable investigation as to whether primary sequestration of metals in photosynthetic tissues is restricted to Mn. Methods: Gossia species known to accumulate nickel (Ni) or aluminum (Al) in addition to Mn were sampled in the field. Complementary proton- and electron-probe data were combined to evaluate in vivo microdistribution patterns of excessively accumulated foliar metals. • Key results: It was discovered that in addition to Mn and Ni, Gossia fragrantissima accumulated foliar zinc (Zn) and cobalt (Co), with Mn, Ni, and Co most highly localized in mesophyll cells and Zn primarily located in the upper epidermis. In G. hillii, Mn and Al were highly concentrated in the palisade and epidermis, respectively. Conclusions: This investigation provides evidence that the primary disposal of excess foliar metals in photosynthetic cells is not exclusive to Mn. It offers rare intrageneric perspective on metal compartmentation, pointing to significant variation among tonoplastal metal transporters associated with detoxification. © 2013, Botanical Society of America.
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    Structure and transformation of oxy-hydroxide films on Ni anodes below and above the oxygen evolution potential in alkaline electrolytes
    (Elsevier, 2015-06-20) Mellsop, SR; Gardiner, A; Johannessen, B; Marshall, AT
    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.