Browsing by Author "De Marco, R"

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    The application of neutron reflectometry and atomic force microscopy in the study of corrosion inhibitor films
    (Elsevier B. V., 2006-11-15) John, D; Blom, ACM; Bailey, S; Nelson, A; Schulz, JC; De Marco, R; Kinsella, B
    Corrosion inhibitor molecules function by adsorbing to a steel surface and thus prevent oxidation of the metal. The interfacial structures formed by a range of corrosion inhibitor molecules have been investigated by in situ measurements based on atomic force microscopy and neutron reflectometry. Inhibitors investigated include molecules cetyl pyridinium chloride (CPC), dodecyl pyridinium chloride (DPC), 1-hydroxyethyl-2-oleic imidazoline (OHEI) and cetyl dimethyl benzyl ammonium chloride (CDMBAC). This has shown that the inhibitor molecules adsorb onto a surface in micellar structures. Corrosion measurements confirmed that maximum inhibition efficiency coincides with the solution critical micelle concentration. Copyright © 2006 Elsevier B.V.
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    The application of neutron reflectometry and atomic force microscopy in the study of corrosion inhibitor films
    (The Bragg Institute, Australian Nuclear Science and Technology Organisation, 2005-11-27) John, D; Blom, ACM; Bailey, S; Nelson, A; Schulz, JC; De Marco, R; Kinsella, B
    In the search for new, superior and environmentally friendly corrosion inhibitor molecules, it is important to understand their mechanism of inhibition. Characterising the chemical and physical nature of the adsorbed inhibitor layer is a major part of understanding this mechanism. An accurate account of this character necessitates the use of surface analysis techniques that are capable of in-situ measurements. Ex-situ techniques are likely to cause changes either by oxidation of the metal and corrosion product film or rearrangement and loss of the inhibitor film during exposure to air and during the drying and analysis under vacuum. Neutron reflectometry in combination with atomic force microscopy provides the capability of in-situ surface analysis of thin interfacial layers. These complementary techniques make it possible to investigate the structure and orientation of molecules on a surface. which can ultimately assist in gaining an insight into the inhibitor mechanism. This paper will explore how these techniques can be used to determine the mechanism of corrosion inhibitors, with particular emphasis on surfactant molecules used to prevent carbon dioxide corrosion of steel during petroleum production. Results will be presented from experiments using the aforementioned in-situ surface analysis with generic corrosion inhibitor molecules cetyl pyridinium chloride (CPC), dodecyl pyridinium chloride (DPC), 1-hydroxyethyl-2-oleic imidazoline (OHEI) and cetyl dimethyl benzyl ammonium chloride (CDMBAC). These results will be further discussed with respect to the observed inhibition of carbon dioxide corrosion of carbon steel electrodes. © The Authors
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    Controlled one‐pot synthesis of nickel single atoms embedded in carbon nanotube and graphene supports with high loading
    (Wiley, 2020-04-09) Zhao, S; Wang, T; Zhou, G; Zhang, L; Lin, C; Veder, JP; Johannessen, B; Saunders, M; Yin, L; Liu, C; De Marco, R; Yang, SZ; Zhang, Q; Jiang, SP
    Single‐atom catalysts (SACs) have attracted much attentions due to the advantages of high catalysis efficiency and selectivity. However, the controllable and efficient synthesis of SACs remains a significant challenge. Herein, we report a controlled one‐pot synthesis of nickel single atoms embedded on nitrogen‐doped carbon nanotubes (NiSA−N−CNT) and nitrogen‐doped graphene (NiSA−N−G). The formation of NiSA−N−CNT is due to the solid‐to‐solid rolling up mechanism during the high temperature pyrolysis at 800 °C from the stacked and layered Ni‐doped g‐C3N4, g‐C3N4−Ni structure to a tubular CNT structure. Addition of citric acid introduces an amorphous carbon source on the layered g‐C3N4−Ni and after annealing at the same temperature of 800 °C, instead of formation of NiSA−N−CNT, Ni single atoms embedded in planar graphene type supports, NiSA−N−G were obtained. The density functional theory (DFT) calculation indicates the introduction of amorphous carbon source substantially reduces the structure fluctuation or curvature of layered g‐C3N4‐Ni intermediate products, thus interrupting the solid‐to‐solid rolling process and leading to the formation of planar graphene type supports for Ni single atoms. The as‐synthesized NiSA−N−G with Ni atomic loading of ∼6 wt% catalysts shows a better activity and stability for the CO2 reduction reaction (CO2RR) than NiSA−N−CNT with Ni atomic loading of ∼15 wt% due to the open and exposed Ni single atom active sites in NiSA−N−G. This study demonstrates for the first time the feasibility in the control of the microstructure of carbon supports in the synthesis of SACs. © 1999-2024 John Wiley & Sons, Inc or related companies. All rights reserved.
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    Elimination of undesirable water layers in solid-contact polymeric ion-selective electrodes
    (American Chemical Society, 2008-09-01) Veder, JP; De Marco, R; Clarke, G; Chester, R; Nelson, A; Prince, KE; Pretsch, E; Bakker, E
    This study aimed to develop a novel approach for the production of analytically robust and miniaturized polymeric ion sensors that are vitally important in modem analytical chemistry (e.g., clinical chemistry using single blood droplets, modem biosensors measuring clouds of ions released from nanoparticle-tagged biomolecules, laboratory-on-a-chip applications, etc.). This research has shown that the use of a water-repellent poly(methyl methacrylate)/poly(decyl methacrylate) (PMMA/PDMA) copolymer as the ion-sensing membrane, along with a hydrophobic poly(3-octylthiophene 2,5-diyl) (POT) solid contact as the ion-to-electron transducer, is an excellent strategy for avoiding the detrimental water layer formed at the buried interface of solid-contact ion-selective electrodes (ISEs). Accordingly, it has been necessary to implement a rigorous surface analysis scheme employing electrochemical impedance spectroscopy (EIS), in situ neutron reflectometry/EIS (NR/EIS), secondary ion mass spectrometry (SIMS), and small-angle neutron scattering (SANS) to probe structurally the solid-contact/membrane interface, so as to identify the conditions that eliminate the undesirable water layer in all solid-state polymeric ion sensors. In this work, we provide the first experimental evidence that the PMMA/PDMA copolymer system is susceptible to water "pooling" at the interface in areas surrounding physical imperfections in the solid contact, with the exposure time for such an event in a PMMA/PDMA copolymer ISE taking nearly 20 times longer than that for a plasticized poly(vinyl chloride) (PVC) ISE, and the simultaneous use of a hydrophobic POT solid contact with a PMMA/PDMA membrane can eliminate totally this water layer problem. © 2008, American Chemical Society
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    Evidence for a surface confined ion-to-electron transduction reaction in solid-contact ion-selective electrodes based on poly(3-octylthiophene)
    (American Chemical Society, 2013-11-05) Veder, JP; De Marco, R; Patel, K; Si, P; Grygolowicz-Pawlak, E; James, M; Alam, MT; Sohail, M; Lee, J; Pretsch, E; Bakker, E
    The ion-to-electron transduction reaction mechanism at the buried interface of the electrosynthesized poly(3-octylthiophene) (POT) solid-contact (SC) ion-selective electrode (ISE) polymeric membrane has been studied using synchrotron radiation-X-ray photoelectron spectroscopy (SR-XPS), near edge X-ray absorption fine structure (NEXAFS), and electrochemical impedance spectroscopy (EIS)/neutron reflectometry (NR). The tetrakis[3,5-bis(triflouromethyl)phenyl]borate (TFPB?) membrane dopant in the polymer ISE was transferred from the polymeric membrane to the outer surface layer of the SC on oxidation of POT but did not migrate further into the oxidized POT SC. The TFPB? and oxidized POT species could only be detected at the outer surface layer (≤14 ?) of the SC material, even after oxidation of the electropolymerized POT SC for an hour at high anodic potential demonstrating that the ion-to-electron transduction reaction is a surface confined process. Accordingly, this study provides the first direct structural evidence of ion-to-electron transduction in the electropolymerized POT SC ISE by proving TFPB? transport from the polymeric ISE membrane to the oxidized POT SC at the buried interface of the SC ISE. It is inferred that the performance of the POT SC ISE is independent of the thickness of the POT SC but is instead contingent on the POT SC surface reactivity and/or electrical capacitance of the POT SC. In particular, the results suggest that the electropolymerized POT conducting polymer may spontaneously form a mixed surface/bulk oxidation state, which may explain the unusually high potential stability of the resulting ISE. It is anticipated that this new understanding of ion-to-electron transduction with electropolymerized POT SC ISEs will enable the development of new and improved devices with enhanced analytical performance attributes.© 2013, American Chemical Society.
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    Evidence of a water layer in solid-contact polymeric ion sensors
    (Royal Society of Chemistry, 2008-01-01) De Marco, R; Veder, JP; Clarke, G; Nelson, A; Prince, KE; Pretsch, E; Bakker, E
    This paper presents the very first direct structural evidence for the formation of a 100 +/- 10 angstrom water layer in coated-wire polymeric-membrane ion-selective electrodes (ISEs). © 2008, Royal Society of Chemistry
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    Investigating HPA functionalized mesoporous silica materials for use as high temperature proton exchange membranes
    (Australian Institute of Nuclear Science and Engineering (AINSE), 2012-12-07) Lamb, K; De Marco, R; Jiang, SP; Peterson, VK
    High temperature (>100°C) proton exchange membrane fuel cells (HT-PEMFC) are solid energy conversion devices that electrochemically convert chemical energy (eg. from alcohols) into electricity. HT-PEMFCs are more efficient than low temperature PEMFCs due to elimination of carbon monoxide poisoning and faster oxidation kinetics. Various types of proton exchange membranes have been explored, such as nonfluorinated hydrocarbon polymers, or hybrid Nafion-based membranes. While these materials have their advantages, they dehydrate at high temperatures, leading to a significant reduction in proton conductivity. Recently, we found that heteropolyacids (HPA) such as tungstophosphiric acid (abbreviated as HPW) can be used to functionalize ordered mesoporous silica (MSN) to make nanocomposites PEMs. While these nanocomposites have shown promising preliminary results as HT-PEMs, the ways in which changes to the structure of these materials affect the proton exchange properties are largely unknown. Analysis techniques such as ex- and in-situ HR-FTIR, SAXS, SANS, and QENS will be used to build an understanding of the membrane structure and proton diffusion mechanisms of these HT-PEMs, thereby determining the best performance HPA-MSNs for use in direct alcohol fuel cells.
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    Iron single atoms on graphene as nonprecious metal catalysts forhHigh‐temperature polymer electrolyte membrane fuel cells
    (Wiley, 2019-03-13) Cheng, Y; He, S; Lu, SF; Veder, JP; Johannessen, B; Thomsen, L; Saunders, MJ; Becker, T; De Marco, R; Li, QF; Yang, SZ; Jiang, SP
    Iron single atom catalysts (Fe SACs) are the best‐known nonprecious metal (NPM) catalysts for the oxygen reduction reaction (ORR) of polymer electrolyte membrane fuel cells (PEMFCs), but their practical application has been constrained by the low Fe SACs loading (<2 wt%). Here, a one‐pot pyrolysis method is reported for the synthesis of iron single atoms on graphene (FeSA‐G) with a high Fe SAC loading of ≈7.7 ± 1.3 wt%. The as‐synthesized FeSA‐G shows an onset potential of 0.950 V and a half‐wave potential of 0.804 V in acid electrolyte for the ORR, similar to that of Pt/C catalysts but with a much higher stability and higher phosphate anion tolerance. High temperature SiO2 nanoparticle‐doped phosphoric acid/polybenzimidazole (PA/PBI/SiO2) composite membrane cells utilizing a FeSA‐G cathode with Fe SAC loading of 0.3 mg cm−2 delivers a peak power density of 325 mW cm−2 at 230 °C, better than 313 mW cm−2 obtained on the cell with a Pt/C cathode at a Pt loading of 1 mg cm−2. The cell with FeSA‐G cathode exhibits superior stability at 230 °C, as compared to that with Pt/C cathode. Our results provide a new approach to developing practical NPM catalysts to replace Pt‐based catalysts for fuel cells. © 1999-2024 John Wiley & Sons, Inc or related companies. © 2019 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
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    Is ballistic transportation or quantum confinement responsible for changes in the electrical properties of thin polymer films?
    (Royal Society Chemistry, 2012-11-26) Veder, JP; Patel, K; Lee, J; Alam, MT; James, M; Nelson, A; De Marco, R
    Resistivities of thin polymer films increase abruptly with decreasing thickness, although the corresponding decline in resistance plateaus below a certain thickness. One can jump to the incorrect conclusion that quantum confinement and surface scattering are responsible for this behaviour, and we highlight the pitfalls of committing such an error. © 2012, Royal Society of Chemistry
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    Neutron and synchrotron characterisation techniques for hydrogen fuel cell materials
    (Australian Nuclear Science and Technology Organisation, 2021-11-24) Lamb, K; Kirby, N; Bartlett, JR; Peterson, VK; Appadoo, D; Jiang, SP; De Marco, R
    Hydrogen fuel cells and other renewable energy technologies have specific materials and functional needs which can be more fully understood using neutron and synchrotron characterisation techniques. In this presentation, a materials which has applications in proton exchange membranes is studied with a variety to techniques to develop a comprehensive understanding of the functional-structural relationship. The materials used here is phosphotungstic acid (HPWA) stabilised in an ‘inert’ mesoporous silica host material. This aim of this research is to develop an understanding of the interaction between the HPWA and the silica and whether different structures or surface chemistries have advantageous or detrimental effects. Two silica symmetries used were Ia3 ̅d (face centred cubic bi-continuous) and P6mm (2D hexagonal with cylindrical pores) which were vacuum impregnated with solutions of HPWA in a range of concentrations. The resulting powder samples were then analysed using small angle x-ray scattering (SAXS), inductively coupled plasma emissions spectroscopy (ICP-OES), nitrogen gas adsorption/desorption, near edge X-ray absorption fine structure (NEXAFS/X-ray absorption near edge structure/XANES) of the O and Si k-edges, Fourier transform infra-red spectroscopy (FTIR), Raman spectroscopy, and then formed into a disk using polyethylene as the binder for electrical impedance spectroscopy (EIS). The insights gained from this systematic study indicate that the surface chemistry of the silica host has a significant effect on the performance, uptake and interactions with the HPWA anions, where lower concentrations of HPWA result in stronger host:HPWA interactions but lower conductivity. © The Authors