Palladyom eşektrodun seçici elektrokatalitik özelliklerinin D-Glikozun elektrooksidsyonunda belirlenmesi
The Determination of selective properties of palladium electrode in D-Glucose electrooxidation
- Tez No: 39367
- Danışmanlar: PROF.DR. FİGEN KADIRGAN
- Tez Türü: Doktora
- Konular: Kimya, Chemistry
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1992
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 180
Özet
ÖZET Altmışlı yıllardan bu yana glikozun elektrooksidasyonu pek çok araştırmacı için ilgi çekici bir konu olmuştur. Bu araştırmalar tıpta gerek biyolojik yakıt pilleri gerekse elektrokimyasal biyosensörlerdeki uygulamaları nedeni ile ilgi çekmiştir. Bu uygulamalar arasında Şeker hastaları için kandaki Şeker konsantrasyonunu saptamada elektrokimyasal biyosensörlerin geliştirilmesini, ayrıca kalp pilleri ve hatta yapay kalpler için güç kaynağı olarak kullanılan glikozlu yakıt pillerinin gerçekleştirilmesini sayabiliriz. Ayrıca glikozun elektrokimyasal oksidasyonu, değişik şeker türevlerinin eldesi, dolayısıyla elektrosentez amacıyla da üzerinde çalışılan bir konu olmuştur. Çalışmanın ilk bölümünde D-glikozun elektrooksidasyonu bazik ortamda palladyum elektrot üzerinde gerçekleştirilmiş ve reaksiyon kinetiği incelenmiştir. Daha sonra ise palladyum elektrodun aktivitesini arttırmak amacıyla upd(adatom) yöntemi kullanılmış, bir diğer bölümde ise palladyum altın ile sabit potansiyelde alaşım haline getirilmiştir. Bu Çalışmaların yanisıra, çözeltide glikoza ait türleri tanımlayabilmek amacıyla polarimetrik, reaksiyon ara ürünlerini tespit etmek amacıylada FT/IR ile spektroskopik denemeler gerçekleştirilmiştir. Çalışmaların tümü üç elektrotlu bir hücrede siklik voltametri tekniği uygulanarak gerçekleştirilmiştir. vi
Özet (Çeviri)
SUMMARY THE DETERMINATION OF SELECTIVE PROPERTIES OF PALLADIUM ELECTRODE IN D-GLUCOSE ELECTROOXIDATION Up to now, with the exception of hydro-electrical power, almost all our energy resources are based on fossil fuels such as petroleum, coal and natural gas. The Earth's reserves of fossil fuels have been formed though the transformation of materials of organic origine under the action enormous heat and pressure for millions of years ago during the geological ages. But these reserves are somewhat limited and many of“the^ will be probably exhausted by the middle of the 21 century. Consequently, the world will face a very serious energy crisis. Since the world population increases rapidly, while the reserves of fossil fuels do decline dramatically, the scientists are in search of new energy sources. During the 40 years, since World War 2, significant advances have been made in battery and electrochemical devices tecnology. At the start of World War 2, the Leclanche zinc-carbon primary cell and lead-acid and the Edison nickel-iron secondary batteries were the predominant types, with few other battery systems available. While these original battery systems are still important and have greatly improved performance characteristics, many other battery systems and fuel cells are now in use, with a wide range of size and configuration. The number and variety of battery applications have increased substantially, as evidenced by the remarkable growth of the battery market, from under half a billion (at the manufacturer's level) in 1947 to almost $10 billion annually in the early 1980 's. This interest in batteries and electrochemical tecnology, heightened by the recent emphasis on fuel cell and battery development for portable electronics, energy storage and electric vehicles, has resulted in substantial literature in electrochemical research and development, including the publication of several texts covering different phases of battery tecnology. The fuel cell can be considered a battery except that one or both of the reactants are not permanently contained in the electrochemicall cell but are fed into it from an external source when power is desired. Thus, the cell can operate continuously as long as reactans are ?Üsupplied and.Ithe i internal cell electrodes and components Temain unchanged» The -anode materials, or fuel, is usually gaseous or liqued such as hydrogen, hydrazine, hydrocarbons, alcohols,... (compared with metal anodes generally used in batteries) and oxygen or air is the oxidant. Â1 thought fuel cell were inverted nearly 150 years ago, the first practical application was in the I960' s as a spacecraft power source for Gemini and Apollo missions. Storage batteries were adequate for short space missions-, but fuel cells were necessary to provide power (and energy) for the extented missions. Future fuel cell applications will include remote power generation (space, undersea), military, commercial electric power generation (by both electric ajld gas utility industries), and possibly in the longer range, hybrid electric vehicles. Fuel.cell, produce power by an electrochemical rather than a thermal cycle and are not subject to the Carnot cycle limitation of thermal machines, thus offering the potential for highly efficient conversion of chemical to electrical energy. Furthermore, the efficiency is essentially independent of size, small power plants operate nearly as efficiently as large ones. Fuel cell power plants are quiet and clean, the byproducts being water, carbondioxide and nitrogen. They can be considered for applications where noxious emissions or noise would be objectionable and where water is unavailable, and they can be sited where used rather than in a remote location. Also, like batteries, they are inherently modüler down to the level of the individual cell. These properties of fuel cell power plants lead to their consideration for a variety of applications. Fuel cell power plants operating on hydrogen and oxygen offer high energy density; that is, are relatively small weight and volume of total system can produce large energy outputs. Thus, fuel cells are preferred power generators in remote applications where system weight and volume are important parameters, e.g., space, undersea Fuel cell power plants operating on logistic fuels and air offer the potential for environmentally acceptable highly efficient, and low - cost power generation. Thus, fuel cells are being seriously considered for applications where these attributes are important, e.g., military and commercial electric power generation and, possibly, vehicles. Hydrogen and oxygen electrodes were investigated in details for a long time. The latter studies show that, electrodes, has soluble fuel such as alcohols have interesting results. They have high solubility and low vapour pressure. Moreover, since they can be easily viiideposited and obtained from biomass, the most of the researces are being focused on the development of alcohol's fuel cell. Extentive work has been done during the last twenty years on the oxidation of alcohols, poly-alcohols and carbohydrates at noble metal electrodes, both directed toward the development of analytical sensors and hyrocarbon fuel cells. Recenty, electrooxidation of glucose has become the subject of many investigations in connection with the problem of devising both electrochemical sensors for determining the sugar concentration in blood and implantable glucose fuel cells intended for artificial hearts and heart pacers. A miniature, accurate and reliable glucose sensor is highly desirable for the management of diabetes mellitus. It has been proposed to use such a sensor to control an insulin delivery system or to asses the effectiveness of a pancreatic tissue transplant. Nature accomplishes the oxidation of glucose in a very elegant manner with the participation of complicated enzyme systems. The resulting energy of the chemical reaction is partly converted into mechanical energy with high efficiency (app. 30%). Obviously, we are not able to compete with nature in this respect. But the utilization of body inherent energy reserves is indeed of considerable interest in biomedical engineering. Greet efforts were made to provide energy for a totally implantable blood pump of an artificial heart using biofuel cells. But, yet, no catalyst system is available which enables the quantitative oxidation of glucose to carbon dioxide rapidly i.e. with a high current density. Recently, the electrochemical oxidation of glucose on metal electrodes has been studied with special interest because of its importance for possible electrical devices to be used in living organisms. Thus, efforts were made to determine the possibility of utilizing glucose (dextrose in commercial) as a fuel in an implantable biofuel cell useful as a power source for electronic devices of medical interest. The possibility of a biological sensor of glucose level in relation to an artificial pancreas was also considered. A critical rewiew of the available literature related to this reaction shows that different mechanistic interpretations were postulated for the electro-oxidation of glucose. D-glucose belong to the class of organic compounds knowns as carbohydrates. Carbohydrates are the ultimate axsource söf -most of our food», ^hen eat^en -by an animal, it can be carried ”by the bloodstream to the tissues, where it is oxidized, ultimately to carbon dioxide and water, with the release of energy originally supplied as sunlight. The investigations showed that this reaction looks like the electrochemical oxidation of glucose on metal electrodes. In first part of our research, the electrooxidation of glucose at palladium electrode in alkaline media was investigated. A" systematic study was realized for which determine the kinetic parameters of reaction and the effect of sweep rate and sweep border, the effect of the concentrations of ions, the effect of temperature, etc. It was found that the role of palladium in oxidation processes differs from other metals. Apparenty,. the electrochemical oxidation of such a complicated molecule as glucose, which can basically release twentyfour electrons while undergoing various oxidation steps, is a complex process. The first two electrons are readily transferred. But in general, the immediate oxidation product, gluconic acid, reacts more lethargically than glucose and becomes rate determining. The oxidation of gluconic acid is more difficult. So, the intermediate products which are lethargic to further reaction are considered responsible for the current decrease by blocking the catalyst surface. In second part of study, the effect of upd adatoms such as Pb, Bi, Tl, Cu, Cd on the catalytic activity of palladium electrode towards the electrooxidation of D-glucose in alkaline media is studied. The catalysis of glucose oxidation on metal electrodes with upd submonolayers of heavy metals may have a practical value in the development of biological conversion systems, since glucose and other monosaccharides can be used as fuels in biofuel cells in vitro. The catalytic phenomena were interpreted in terms of the decrease of the electrode poisoning resulting from a stable gluconolactone-type adsorbate, according to the model of the third-body effect in electrocatalysis. Preliminary studies on this technique presented also in references. Results have shown that the catalysis of glucose oxidation oh Pd by upd submonolayers is influenced markedly. by the steric and structual characteristics of this molecule. The electrooxidation of organic molecules leads to the production of strongly adsorbed intermediates which poison the electrocatalyst surface, while the enhancement of the catalytic activity of the bare electrode metal by large upd heavy metal adatoms decreases the electrode poisoning according to the third body mechanism. Since xthe electrocatalytic properties depend on these first layers, it is very important to increase the stability of the electrode surface. Therefore, in third part of study, palladium-gold alloys were prepared electrochemically. The electrocatalytic properties of such alloys have been explored for a few reactions among them the hydrogen evolution and the oxygen reduced. For all these studies, conventional cyclic voltammetry is used in conjunction with a three electrodes electrochemical cell, the working electrode potential being controlled via a mercurous sulphate reference electrade (MSE). Cyclic voltammetry allows to estimate the superficial composition of the working electrode by measuring the potential position of the reduction peak of the adsorbed oxygen layer, which is build durig the anodic sweep, according to the method developped by RAND and WOODS. For gold-palladium alloys, this is a very convenient method since the two reduction peaks on pure metals are very well separated at least by 0.5V from each other. It is assummed that the peak potential of the alloy is a lineer function of its superficial composition. Owing to the multiplicity of the plausible chemical structures of glucose in solution and the difference of reactivity which may result to obtain the additional information on the above conditions, a systematic study is made by polarimetry. According to the [a] (specific rotation angles) values obtained, it is possible to conclude that there is a chemical evolution of the solution with time in alkaline media. Finally, to determine byproduct, a potential program was applied and samples were examined by FT/IR spectrometer. xi
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