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Characterization of Thin Film Photoanodes for Solar Water Splitting
No full textFor centuries, mankind has mostly used fossil fuels, i.e., natural gas, coal, and oil for its energy needs. With the fast rise of the world population and the rising standards of living in the developing countries, the amount of energy the world is going to need in the coming decades will grow enormously. Due to environmental concerns and the need to secure the energy supply, more actions have to be taken in the development and implementation of cleaner technologies, based on solar, wind, geothermal power, and biomass, combined with storage technologies such as batteries and hydrogen. Moreover, to fulfill the future global energy demand, all of the available energy sources will be needed. Despite the fact that solar energy is abundant, clean, and widely available, only a small percentage of this energy is utilized through conversion to electricity by photovoltaic systems. This is partly due to the need for smart technological inventions to make the alternative energy cost-effective and competitive with the conventional energy production. The Netherlands intends to increase the percentage of energy produced by sustainable sources from 4% nowadays to 20% in 2020. When considering sustainable energy production, also energy storage has to be investigated, since especially solar and wind energy are not continuous. In the chain of solar energy production and the need for energy storage, hydrogen is a promising storage candidate due to its high gravimetric energy density and its nonpollutive combustion product, water. Nowadays, hydrogen can be produced by a number of processes, such as electrolysis of water, steam reforming of natural gas, and biomass conversion, which directly or indirectly release large amounts of carbon dioxide into the atmosphere. An elegant alternative will be the use of solar energy for the electrolysis of water in a photoelectrochemical cell. Direct photoelectrolysis has the potential to be economically more attractive than coupled systems of photovoltaic cells and electrolysers. Additional information regarding this subject can be found in Chapter 1, as well as the necessary requirements for the photoelectrodes. In this thesis three different metal oxides, TiO2, InVO4, and Fe2O3 are investigated as photoanodes for water splitting applications. The aim of the research presented in this thesis is two-fold. First, the use of low-cost deposition techniques for the preparation of efficient thin-film photoanodes is explored. Special attention is given to the possibility to introduce dopants in a controlled manner. Second, the influence of the presence of ionic point defects on the photoelectrochemical performance of the materials is investigated. Titanium dioxide has long been considered as one of the most promising semiconductors for photoelectrolysis applications due to its low cost, non-toxicity, and excellent stability against corrosion. However, because of its wide bandgap (3.2 eV for anatase) the utilization of TiO2 typically remains confined to the UV light region, which constitutes only a small fraction (2-3%) of the solar radiation reaching the earth surface. Therefore, shifting its photoresponse into the visible range of the solar spectrum would enhance its potential for chemical solar energy conversion. Attempts to achieve this performance are typically focused on adding dopants. In Chapter 2 Fe- and C-doped TiO2 thin films have been investigated. Pulsed spray pyrolysis is employed to deposit high quality dense films. The prepared films are crystalline with an anatase structure and a post-deposition anneal does not change the morphology. For the Fe-doped TiO2 a small sub-bandgap photoresponse is observed, which is attributed to the presence of additional states located just above the valence band. Little or no visible-light photoresponse is observed for the C-doped anatase TiO2, which is attributed to a (too) low carbon content. However, the photocurrent at h?>Eg is significantly larger for C-doped TiO2 than for undoped TiO2. The strong enhancement of UV photoresponse is most likely caused by a change in the electronic structure of the material due to the presence of carbon and/or related defects. Photoluminescence measurements suggest that the defects present in oxidized carbon-doped anatase resemble those present in undoped, partially reduced TiO2. Although the exact nature of these defects is unknown, impedance measurements reveal a donor density of 1019-1020 cm-3 in C-doped TiO2. The high UV photoresponse is rather surprising for such a high donor density, and illustrates the intriguing, but still poorly understood properties of anion dopants. From the synthesis point of view, the preparation of carbon-doped TiO2 photoanodes was found to be challenging. A more simple approach is to prepare C-doped powders by solid-state reactions at high temperatures. Such a system can serve as a convenient screening method for selecting suitable anion dopants by analyzing the evolved gases, even if the efficiencies are very low. In Chapter 3 the focus is on the addition of carbon as dopant to anatase TiO2 by a post-deposition thermal treatment in a hexane-rich environment. Both thin films prepared by spray pyrolysis and mesoporous TiO2 photoelectrodes prepared by doctor-blading a paste of TiO2 nanoparticles are investigated. It is found that the carbon is mainly located at the surface of the TiO2. While it causes a black coloring of the mesoporous TiO2 film, it does not enhance the photocatalytic activity in the visible part of the spectrum. Only a small amount of carbon (3 and it has a near-optimal bandgap of 2.1 eV that enables up to 32% sunlight absorption. It is also an abundant and inexpensive semiconductor. However, certain intrinsic properties of Fe2O3 limit its performance as a photoelectrode. It shows a poor conductivity, which often leads to a high recombination rate, the energy level of the conduction band is too low for hydrogen evolution, it has slow kinetics for water oxidation, and a modest optical absorption coefficient. The main goal of the research in this chapter is on the preparation of Fe2O3 nanorods perpendicular to the substrate. Such a morphology could improve the efficiency of Fe2O3 photoanodes by decreasing the diffusion path length of the photo-generated holes. To achieve this, electrodeposition of Fe followed by thermal oxidation (EDOX) is explored as a new method to obtain these photoelectrodes efficiently in a short time and with the possibility to control the morphology. It is observed that after reaching a certain thickness or at a sufficiently high deposition current (2 mA/cm2) nano-sized needle- like features start to form. A further increase of the deposition current to 3 mA/cm2 results in a columnar growth consisting of small irregular crystallites stacked on top of each other. In contrast, it has been observed that when a Si precursor is present in the electrolyte solution during the electrodeposition, compact dense Fe2O3 films consisting of spherical particles are formed after the post-deposition oxidation. XRD analysis and Raman spectroscopy show that the Fe2O3 films mainly consist of the ?- Fe2O3 hematite phase. An important advantage of the EDOX method is that low-cost equipment can be used. Moreover, the direct thermal oxidation of electrodeposited Fe avoids the formation of undesired intermediate phases, such as FeOOH. Finally, the electrodeposition process takes place in a non-aqueous solvent, which allows the use of certain dopant precursors (e.g. TiCl4) that cannot be used in aqueous systems. This is an important advantage of this approach compared to other efforts in the literature. Although the EDOX method has been successfully demonstrated, an important remaining challenge is to improve control over the morphology and the doping density. Further improvements of the morphology may be possible by adding additives to the electrolyte solution, or by controlling the process parameters during oxidation of the electrodeposited iron. In conclusion, it has been demonstrated in this thesis that high-quality metal oxides can be prepared by low-cost techniques. Concomitantly, the impact of the ionic point defects on the performance of those photoanode materials is addressed and important material properties are determined. The attempts to enhance the visible-light response does not always result in higher efficiencies, due to low dopant concentrations in TiO2 films, poor electronic properties of InVO4 thin films, and morphology challenges for Fe2O3 to overcome its limitation as photoanode material. Nevertheless, important properties of the thin film photoanodes have been investigated and determined. No binary oxide solely can split water with a reasonable efficiency unless a tandem cell approach with suitable oxides is used. In principle, a lot can be gained by directing future research efforts towards ternary and even more complex metal oxides. In this case, however, the control over the stoichiometry of the metal ions remains challenging compared to simple binary oxides as has been demonstrated by the results on InVO4. While for some of the alternative energy sources technological breakthroughs have been achieved and new technologies are developed, for the hydrogen economy and in particular for the photoelectrochemical water splitting with metal oxides, more research is needed in developing low-cost techniques to make highly structured electrodes with large aspect ratios, to develop synthesis and/or doping strategies to suppress undesired defects present in the ternary oxides with non-stoichiometric metal:metal ratios, and not the least, in finding new and improving existing materials. When these challenges are met, photoelectrochemical water splitting may emerge as an economically viable and truly renewable pathway towards clean hydrogen.Materials for Energy Conversion and StorageApplied Science
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
Author Under Sail The Imagination of Jack London, 1893-1902
No full textIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Intro -- Title Page -- Copyright Page -- Dedication -- Contents -- Acknowledgments -- Introduction -- 1. Spirit Truth -- 2. From Absorption to Theatricality and Back Again -- 3. "I Will Build a New Present" -- 4. Sons as Authors -- 5. Fathers as Publishers -- 6. The Daughter as Author -- 7. Lovers as Authors -- 8. At Sea with the Family -- 9. Yellow News, Yellow Stories -- 10. The Return Home -- Notes -- Bibliography -- Index -- About Jay WilliamsIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Description based on publisher supplied metadata and other sources.Electronic reproduction. Ann Arbor, Michigan : ProQuest Ebook Central, YYYY. Available via World Wide Web. Access may be limited to ProQuest Ebook Central affiliated libraries
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