1,720,973 research outputs found
Combinatorial synthesis of gold-based thin films for improved electrocatalytic conversion of CO2 to CO
No full textCarbon dioxide electroreduction (CO2ER) was studied on 35 gold-based thin film catalysts sputtered on glassy carbon disks. A sputter-down setup was used for the deposition of these thin films in a combinatorial manner. Zinc and silver were employed in combination with gold in order to obtain new catalysts. Linear sweep voltammetry was employed to obtain the selectivity profile of each catalyst. Among the 35 catalysts, three ternary combinations (Au14Ag34Zn52, Au32Ag51Zn17, and Au16Ag10Zn74) and one binary combination (Au80Zn20) were identified as being active catalysts, reducing the dissolved CO2 in favor of proton reduction. Two ternary catalysts (Au16Ag10Zn74 and Au32Ag51Zn17) exhibited higher selectivity and lower overpotential for CO2ER than the pure metals. The Au80Zn20 binary catalyst exhibited the longest potential range where the selectivity for CO2ER remains constant. A decrease of the gold loading between 18 and 88 % was obtained for these catalysts, suggesting that they are promising candidates for an industrial application of CO2ER. Electrochemical impedance spectroscopy proved that the mechanism of CO2ER, involving two successive one-electron transfers, is identical on pure metals and combined sputtered catalystsResearch Focus Area for Chemical Resource Beneficiation (CRB
The effect of sputtered Pt40Pd57Al3 thin film thickness on SO2(aq) electro-oxidation
No full textThe influence of sputtered Pt40Pd57Al3 thin films of varying thickness, in the as-deposited (AD) and annealed (AN) state, was investigated for the electro-oxidation of aqueous SO2. From physical characterisation (scanning electron microscopy (SEM) and grazing incidence X-ray diffraction (GIXRD)), significant differences were found in the morphology and crystallinity between AD and AN samples. In terms of electrochemical activity, the current output for the AD and AN thin films decreased as the thickness increased, whilst the AN thin films in general resulted in lower current outputs. No specific trend was observed for stability in an acidic environment and a 60 nm Pt40Pd57Al3 thin film proved to be the optimum thickness for aqueous SO2 electro-oxidation. In addition, the 60 nm Pt40Pd57Al3 AN thin film outperformed pure Pt (60 nm, AD and AN) in terms of current density and stability, emphasising the fact that multicomponent electrocatalysts can be superior compared with their pure metal counterpart
Synthesis, characterisation and potential employment of Pt–modified TiO2 photocatalysts towards laser induced H2 production
Full text linkThesis (M.Sc. (Chemistry))--North-West University, Potchefstroom Campus, 2012.The photocatalytic production of H2 from water as well as from a 1:1 methanol:water
solution employing pre–treated TiO2 and various Pt–TiO2 photocatalysts was studied by
using an Nd:YAG laser as irradiation source. The photocatalysts (0.5–, 1–, 1.5– and 2
wt% Pt–TiO2) were prepared by utilizing a photocatalytic reduction method after which
characterisation by various analytical techniques, i.e. XRD, TEM, ICP, SEM, and EDX,
were conducted. XRD clearly indicated that platinum was not present in the crystal
structure of TiO2, but was rather loaded onto the surface of TiO2. TEM analysis
confirmed the presence of Pt on the surface with a particle/cluster size between 11 nm
and 22 nm. SEM showed that repeatable results in respect of surface appearance were
obtained. ICP and EDX indicated that the loading method was successful with only a
slight deviation between the actual amount loaded and the calculated amount loaded.
The impact of the loaded Pt on the band gaps of the different photocatalysts was
investigated by diffuse reflectance spectroscopy (DRS) and calculated by employing
the Kubelka–Munk method. The band gap values shifted sequentially from 3.236eV to
3.100 eV as the loading increased, moving closer to the absorbance region for visible
light. The amount of hydrogen produced from the individual photocatalysts dispersed in
both pure water and aqueous methanol solutions, was measured manually with a gas
chromatograph. As soon as irradiation was initiated, a distinct colour change from
shades of grey to dark blue–grey was observed for all the photocatalysts. XRD
confirmed that it was due to the anatase phase transforming to produce more rutile
phase. No H2 was detected for the various photocatalysts suspended in water, i.e. in
the absence of methanol. The amount of hydrogen produced from the various Pt
photocatalysts suspended in the aqueous methanol solution was found to be the
highest for the 0.5wt%– and 1.5wt% Pt–TiO2 photocatalysts and the lowest for the 2wt%
Pt–TiO2. This could be due to loading Pt above the optimum amount to such an extent,
preventing sufficient light from reaching the TiO2 surface. Pt particles can also touch
and overlap which will decrease Pt contact with TiO2 thus decreasing effective charge
transfer.Master
Investigating sputtered thin film Pt-containing electrocatalysts for SO2(aq) electro-oxidation
Full text linkEnvironmental concerns, social, economic and political pressure, and new technologies are the main factors
driving change in energy systems around the globe. Human life and development are inevitably dependent
on energy and the world is currently significantly reliant on mainly fossil fuels to meet its energy
requirements. Fossil fuels together with nuclear energy both have negative implications for the health of
humans and the quality of the environment. A worthy competitor that can serve as a solution to the depleting
and destructive nature of fossil fuels and nuclear energy is renewable energy. Hydrogen, not only a noncarbon-
containing energy carrier, but the most abundant atom on earth is considered the ultimate clean
energy carrier to be generated from renewable resources. As hydrogen is only found as part of compounds
on earth, it is fairly energy intensive to separate hydrogen into its molecular form, which goes hand in hand
with huge amounts of environmental pollutants being emitted to the atmosphere. The hybrid sulphur (HyS)
cycle, a thermo-electrochemical water splitting process, through the electrochemical oxidation of SO2,
serves as a means of producing hydrogen in a usable form without emitting any harmful pollutants.
Although there are various ways to produce hydrogen, interest in the non-carbon-based HyS cycle as a
potential large scale hydrogen production process, results from the fact that, whereas the anodic reaction
for regular water electrolysis, as another means of producing hydrogen, occurs at a standard potential of
1.23 V (SHE), the anodic reaction in the SO2 depolarised electrolyser (SDE1) occurs at a standard potential
of 0.17 V (SHE), which translates into an energy gain of more than one volt that makes the HyS cycle more
favourable. Insufficient electrocatalyst activity, stability and economic viability are among the most
challenging issues related to technologies for electrochemical energy conversion. An aspect that can
improve the SDE performance and economic viability is improving the anodic reaction of electrochemically
oxidising aqueous SO2. This can be achieved by improving the electrocatalyst for the anodic reaction.
In an effort to address these barriers, combinatorial sputtering, high-throughput screening, and traditional
methods were employed to investigate various thin film electrocatalyst combinations containing alternately
varying content of platinum (Pt), palladium (Pd) and aluminium (Al), towards the electro-oxidation of
aqueous SO2. Throughout the investigation the thin film electrocatalysts were exposed to different physical
and electrochemical treatments and characterisation techniques, resulting in new insights gained. Included
in the list of techniques and methods are combinatorial sputtering, photolithography, high-throughput
screening, cyclic voltammetry, linear polarisation, rapid thermal annealing treatment (RTA), energy
dispersive X-ray spectroscopy (EDX), X-ray diffraction analysis (XRD), X-ray photoelectron spectroscopy
(XPS), atomic force microscopy (AFM) and scanning electron microscopy (SEM). The combinatorial sputtering approach, based on magnetron enhanced plasma sputtering and
photolithography, was developed and employed in the syntheses of the thin film electrocatalysts. A multichannel
potentiostat, connected to a custom manufactured multi-working electrode electrochemical cell,
allowed for high-throughput parallel screening of the deposited electrocatalysts towards the electrooxidation
of aqueous SO2. Employing onset potential and current output as the screening criteria together
with stability tests and the results obtained from physical characterisation (by employment of the above
mentioned techniques), thin films exhibiting satisfactory performance were identified. A Pt3Pd2 thin film,
annealed at 800 °C, and a ternary combination of Pt40Pd57Al3, annealed at 900 °C, were identified as
potential contenders to compete with pure Pt that is currently being employed as the anode material for
electrochemically catalysing the electro-oxidation of SO2. Both Pt3Pd2 and Pt40Pd57Al3 thin films contain
less Pt than a pure Pt thin film, while exhibiting increased electrocatalytic activity, and can serve as a basis
for future studiesNational Research Foundatio
Vulcan carbon as support for sputtered oxygen evolution electrocatalysts
No full textThe development of support structures for electrocatalysts has received a great deal of attention over the last decade, with carbon structures (i.e. nanostructures, Vulcan carbon (VC)) having been studied extensively. Carbon support structures increase the surface area, stability and activity of electrocatalysts in most cases, and can be used to overcome the delamination of thin films. In an attempt to (i) obtain surface structures and areas on SiO2 wafer pads, for combinatorial high-throughput sputtering and screening, that are comparable to glassy carbon (GC), (ii) eliminate delamination of the electrocatalyst and (iii) increase activity and stability, this study focused on VC:Nafion support preparation techniques. Four VC inks were prepared and used as carbon support on GC electrode inserts to analyse their effect on the activity of sputtered Ni thin films (40 nm) towards the oxygen evolution reaction (OER) in alkaline media. Linear sweep voltammetry (LSV) and chronopotentiometry (CP) were employed to compare the catalytic activity and stability of these sputtered Ni thin films on the various VC supports. Results suggest that similar activity compared with IrO2 and RuO2 could be achieved by sputtered Ni on VC:Nafion support, indicating improved Ni utilisation as well as improved short-term stability of the Ni thin films. These results validate the use of VC:Nafion support as substrate for sputtered electrocatalyst
Combinatorial plasma sputtering of PtxPdy thin film electrocatalysts for aqueous SO2 electro-oxidation
No full textA combinatorial sputtering system, based on magnetron enhanced plasma sputtering, was employed in the syntheses of PtxPdy thin film catalysts, and a multi-channel potentiostat allowed for high-throughput parallel screening of the deposited electrocatalysts towards the electro-oxidation of aqueous sulphur dioxide (SO2). Employing onset potential as the screening criterion, it was found that three PtxPdy bimetallic combinations exhibited satisfactory performance with the best compositions being that of Pt3Pd2 and PtPd4. Both these combinations exhibited the same lower onset potential of 0.587 ± 0.004 V, SHE compared to that of pure Pt (0.598 ± 0.011 V, SHE), and in addition contain less Pt in achieving these onset potentialsNational Research Foundation (NRF), South Afric
Evaluation of charge density and the theory for calculating membrane potential for a nano-composite nylon-6,6 nickel phosphate membrane
No full textA new crystalline organic–inorganic nano-composite nylon-6,6 nickel phosphate membrane was
synthesised subsequent to which (a) the physico-chemical characteristics of the membrane were
evaluated employing FTIR, SEM, EDX, TEM, XRD and porosity measurements, and
(b) membrane potential measurements were conducted employing different concentrations
(0.0001 r c (M) r 1) of KCl, NaCl and LiCl 1 : 1 electrolyte solutions. The Teorell, Meyer and
Sievers (TMS) theoretical method was employed for evaluating the charge density of the
synthesised membranes, and the observed data were utilised to calculate membrane potentials
using the extended TMS theory. Charge density for 1 : 1 electrolyte solutions was found to
decrease in the order KCl > NaCl > LiCl, which is in accordance with a decrease in the size of
the cation. The synthesised membrane was found to be cation-selective with the measured
membrane potentials found to be positive in all instances, decreasing in the order
LiCl > NaCl > KCl, which is in accordance with an increase in the size of the cation for the
chosen electrolytes. Observed potential data were used to calculate the transference numbers,
mobilities, distribution coefficients, and charge effectiveness of ions and the theoretically calculated
potential values were found to be in good agreement with the experimentally observed valuesNorth-West University and the PGM Grou
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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