Browsing by Author "Williams, M."

Now showing 1 - 7 of 7
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    Advanced low temperature metal hydride materials for low temperature proton exchange membrane fuel cell application
    (University of the Western Cape, 2010) Ntsendwana, Bulelwa; Lototskyy, Mykhaylo; Williams, M.; Dept. of Chemistry; Faculty of Science
    Energy is one of the basic needs of human beings and is extremely crucial for continued development of human life. Our work, leisure and our economic, social and physical welfare all depend on the sufficient, uninterrupted supply of energy. Therefore, it is essential to provide adequate and affordable energy for improving human welfare and raising living standards. Global concern over environmental climate change linked to fossil fuel consumption has increased pressure to generate power from renewable sources [1]. Although substantial advances in renewable energy technologies have been made, significant challenges remain in developing integrated renewable energy systems due primarily to mismatch between load demand and source capabilities [2]. The output from renewable energy sources such as photo-voltaic, wind, tidal, and micro-hydro fluctuate on an hourly, daily, and seasonal basis. As a result, these devices are not well suited for directly powering loads that require a uniform and uninterrupted supply of input energy.
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    Application of surface-modified metal hydrides for hydrogen separation from gas mixtures containing carbon dioxide and monoxide
    (Elsevier, 2013) Lototskyy, Mykhaylo; Modibane, K.D.; Williams, M.; Klochko, Ye.; Linkov, Vladimir; Pollet, Bruno G.
    Application of surface-modified MH material for H2 separation using temperature/pressure swing absorption–desorption was studied. The substrate alloy had the following composition LaNi3.55Co0.75Al0.4-Mn0.3, and the surface modification was carried out through fluorination followed by aminosilane functionalization and electroless deposition of Pd. The material was found to have good poisoning tolerance towards surface adsorbates, even for the large (rv1.5 kg) batches. Feasibility of its application for H2 separation from gas mixtures (up to 30% CO2 and 100 ppm CO) was demonstrated by testing of a prototype H2 separation system (rv280 g of MH in two reactors), and H2 separation reactor (0.75 kg of MH). The H2 separation was characterized by stable performances in the duration of 250 absorption/desorption cycles. However, the total process productivity was found to be limited by the sluggish H2 absorption (partial H2 pressure 62.5 bar, temperature below 100 °C). In the presence of CO2 and CO, additional deceleration of H2 absorption was observed at space velocities of the feed gas below 5000 h
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    Effect of nanoparticle (Pd, Pd/Pt, Ni) deposition on high temperature hydrogenation of Ti-V alloys in gaseous flow containing CO
    (Elsevier B.V., 2017) Suwarno, S.; Williams, M.; Solberg, J.K.; Yartys, V.A.
    The hydrogenation properties of Ti-V hydrides coated with nanoparticles have been studied in gaseous mixtures of argon and hydrogen with and without additions of 1% CO. Nanoparticles of Pd, Ni, and co-deposited Pd/Pt with particle sizes of ~30-60 nm were formed by electroless deposition on the hydride surfaces. The alloy resistance to CO could be significantly improved by particle deposition. Large amounts of hydrogen were absorbed in a CO-containing gas when Ni and Pd/Pt deposition had been applied, while pure Pd deposition had no positive effect. Ni was found to have a stronger effect than those of Pd/Pt and Pd, possibly because of the size effect of Ni nanoparticles.
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    Hydrogen absorption study of high-energy reactive ball milled Mg composites with palladium additives
    (Elsevier, 2013) Williams, M.; Sibanyoni, J.M.; Lototskyy, Mykhaylo; Pollet, Bruno G.
    Hydrogenation behaviour, structure, morphology and dehydrogenation/re-hydrogenation performances of Mg–Pd nanocomposites prepared by high-energy reactive ball milling in H2 (HRBM) of Mg in the presence of amorphous and crystalline Pd black (0.1–5 wt.%) were studied. Improvements of hydrogenation kinetics during HRBM were observed only for the materials prepared using crystalline Pd black. The obtained nanocomposites were characterised by modest improvements in their dehydrogenation and re-hydrogenation performances associated with the formation of Mg–Pd intermetallides.
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    Magnesium–carbon hydrogen storage hybrid materials produced by reactive ball milling in hydrogen
    (Elsevier, 2013) Lototskyy, Mykhaylo; Sibanyoni, J.M.; Denys, R.V.; Williams, M.; Pollet, Bruno G.; Yartys, V.A.
    Time-resolved studies uncovered kinetics and mechanism of Mg–hydrogen interactions during High energy reactive ball milling in hydrogen (HRBM) in presence of various types of carbon, including graphite (G), activated carbon (AC), multi-wall carbon nanotubes (MWCNT), expandable (EG) and thermally-expanded (TEG) graphite. Introduction of carbon significantly changes the hydrogenation behaviour, which becomes strongly dependent on the nature and amount of carbon additive. For the materials containing 1 wt.% AC or TEG, and 5 wt.% MWCNT, the hydrogenation becomes superior to that for the individual magnesium and finishes within 1 h. Analysis of the data indicates that carbon acts as a carrier of the ‘‘activated’’ hydrogen by a mechanism of spill-over. For Mg–G the hydrogenation starts from an incubation period and proceeds slower. An increase in the content of EG and TEG above 1 wt.% results in the deterioration of the hydrogenation kinetics. The effect of carbon additives has roots in their destruction during the HRBM to form graphene layers encapsulating the MgH2 nanoparticles and preventing the grain growth. This results in an increase of absorption–desorption cycle stability and a decrease of the MgH2 crystallite size in the re-hydrogenated Mg–C hybrid materials (40–125 nm) as compared to Mg alone (180 nm).
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    Nanostructured light weight hydrogen storage materials
    (University of the Western Cape, 2012) Sibanyoni, Johannes Mlandu; Lototskyy, Mykhaylo; Williams, M.
    The main objective of this study was to advance kinetic performances of formation and decomposition of magnesium hydride by design strategies which include high energy ball milling in hydrogen (HRBM), in combination with the introduction of catalytic/dopant additives. In this regard, the transformation of Mg → MgH2 by high energy reactive ball milling in hydrogen atmosphere (HRBM) of Mg with various additives to yield nanostructured composite hydrogen storage materials was studied using in situ pressure-temperature monitoring that allowed to get time-resolved results about hydrogenation behaviour during HRBM. The as-prepared and re-hydrogenated nanocomposites were characterized using XRD, high-resolution SEM and TEM, as well as measurements of the mean particle size. Dehydrogenation performances of the nanocomposites were studied by DSC / TGA and TDS; and the re-hydrogenation behaviour was investigated using Sieverts volumetric technique.
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    Poisoning-tolerant metal hydride materials and their application for hydrogen separation from CO2/CO containing gas mixtures
    (Elsevier, 2013) Modibane, K.D.; Williams, M.; Lototskyy, Mykhaylo; Davids, M.W.; Klochko, Ye.; Pollet, Bruno G.
    Metal hydride materials offer attractive solutions in addressing problems associated with hydrogen separation and purification from waste flue gases. However, a challenging problem is the deterioration of hydrogen charging performances resulting from the surface chemical action of electrophilic gases. In this work, the feasibility study of poisoning tolerance of surface modified AB5-type hydride forming materials and their application for hydrogen separation from process gases containing carbon dioxide and monoxide was carried out. Target composition of La(Ni,Co,Mn,Al)5 substrate was chosen to provide maximum reversible hydrogen capacity at the process conditions. The selected substrate alloy has been shown to be effectively surface-modified by fluorination followed by electroless deposition of palladium. The surface-modified material exhibited good coating quality, high cycle stability and minimal deterioration of kinetics of selective hydrogen absorption at room temperature, from gas mixtures containing 10% CO2 and up to 100 ppm CO. The experimental prototype of a hydrogen separation unit, based on the surface-modified metal hydride material, was tested and exhibited stable hydrogen separation and purification performances when exposed to feedstocks containing concentrations of CO2