Có 20+ tài liệu thuộc chủ đề "công nghệ hóa học dầu khí"
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Hydrogen Evolution. The evolution of hydrogen gas at the cathode is one of the reactions most frequently occurring in industrial cells. On the other hand, hydrogen liberation is the cathodic process in cells containing aqueous solutions or protonated solvents where the wanted reaction takes place at the anode. Also, formation of the gaseous hydrogen accompanies free-metal cor- rosion in an...
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The nature of the reactions leading to deg- radation depends on the class of materials: for metals, corrosion is an electrochemical process, whereas ce- ramics can fail by purely chemical dissolution. In the case of corrosion, metal oxidation reaction (eqn [I]) is coupled with the reduction of species in the environment/electrolyte – the two most typical reactions taking place in...
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Nucleation and growth phenomena are involved in many battery systems, where the electron transfer is coupled to various phase transformations occurring during charge and/or discharge in the active electrode materials. For example, in the leadỜacid battery the electrochemical reactions in- volve formation of different electronically conducting and insulating crystal phases (e.g., lead, lead dioxide (PbO 2. which have a decisive...
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Electrochemical sys- tems at equilibrium maintain the maximum potentiality to perform work intact because DG ¼ nFDE, where DE measures the electrical state of electrochemical systems, F is the Farady constant, and n is the number of electrons.. This is one of the fundamental equations of electro- chemical thermodynamics and expresses the possibility of converting electrical energy (nFDE) into chemical...
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The worldwide thirst for portable consumer electronics in the 1990s has had enormous impact on the field of portable power sources. During this era, lithium-ion batteries, which are based on having lithium ions shuttle between an insertion cathode and an insertion anode, emerged as the rechargeable power source for several lucrative portable electronics markets, including laptops and cell phones. Moreover,...
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To understand the latter it is necessary to consider the effects on various parts of the cell of forcing the cell voltage to assume a value different from that of the equilibrium potential E eq (V) or electromotive force (emf).. In the example of Figure 1, the cell contains hydro- chloric acid as aqueous electrolyte and it divides into two...
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The NEMCA effect is also known as electrochemical promotion or electro- chemical promotion of catalysis (EPOC) or electro- promotion. The NEMCA effect was first reported in 1981 for the case of the oxidation of ethylene (C 2 H 4 ) by gaseous oxygen on porous silver catalyst films deposited on Y 2 O 3 - stabilized ZrO 2 (YSZ), an...
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The electrode reaction of O 2 formation involves four electrons per mole of O 2. This is because of the involvement of high-energy intermediates with complex molecular structure and complicated reaction pathways. As a consequence, the reversible O 2 electrode is not realizable in practice, that is, nothing similar to the reversible H 2 electrode has ever been realized. As...
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The electrochemical cells are of extreme importance in physical chemistry and in everyday life, and several ex- amples of the two main types of electrochemical cells are in widespread use in all areas of manufacture and energy storage. Whenever two phases that have significant electrical conductivities come into contact, there is generally some redistribution of charge, for instance, by charge...
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The rapid growth of the miniature electronic and com- puter-related industries has led to great demand for smaller and lighter batteries with improved safety, en- ergy, and power characteristics. Although the ionic conduction in polymer electrolyte was discovered by D. Polymer electrolytes used in lithium batteries can be classified into three categories: (1) dry polymer electrolytes, (2) gel polymer electrolytes,...
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An ion-selective electrode (ISE) is an example of an electrochemical sensor utilizing the principle of po- tentiometry, or measurement of the cell potential (i.e., ISE against a standard reference electrode) at near-zero current. Under these conditions, the boundary potential at the ISE–solution interface is governed by the laws of electrochemical thermodynamics or is compliant with the famous Nernst equation. >10...
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The NEEs are fabricated by growing metal nanowires in the pores of a template microporous membrane. The density of the pores in the template determines the number of nanoelectrode elements per surface unit and the average distance between the nanoelectrode elements. A scheme of the membrane template procedure is shown in Figure 1.. Charles Martin’s laboratory, shortly followed by others,...
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in this case, the entire thickness of the electrode now becomes available for reaction. If a reaction involves transport of the participating species deep within the electrodes (e.g., as in the case of intercalation electrodes), the use of porous electrodes minimizes this disadvantage and provides access to the electrolyte for a much higher fraction of the electrode. Other advantages include...
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The modern interest for phenomena at the semi- conductor–electrolyte interface dates back to experi- ments performed in the 1950s with germanium, and has extended to most semiconducting materials for reasons of fundamental knowledge or potential application, going from semiconductor processing technology to hetero- geneous photocatalysis to sensors. The aim of this article is to provide a concise survey of the...
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Within solid oxide fuel cells (SOFCs), for instance, nanostructured ionic and electronic con- ducting materials can increase the electrochemical per- formance of the cathode and thus could potentially facilitate lower-temperature operation and thereby pro- vide faster start-up times, improved stability, and less complicated thermal management.. with n, p, and N i the concentrations of electrons e, holes h, and ions...
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Modern research on nonaqueous batteries is focusing on lithium-based systems, which require electrolyte solu- tions stable in the presence of metallic lithium and other anodes such as LiC 6 , which have potentials very close to the Li/Li þ reversible potential. For this reason, this article reviews the state-of-the-art of aprotic solvents, and reviews on protic solvents such as alcohols...
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A battery is defined as a string of individual Galvanic cells, and the basic cell consists of two electrodes (half-cells) immersed in a solution containing an electrolyte com- posed of ions reversible to each of the half-cells. The cell reaction is. Li þ AgCl $ Li þ þ Cl þ Ag ½I In aqueous solution, the two half-cell reactions can...
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Other than in solutions or in ionic liquids, ionic con- duction can take place in the solid state also. Based on the charge of ionic species re- sponsible for the conduction, they are divided into cat- ionic and anionic conductors. then, based on specific species involved in the conduction, they are further subdivided into sodium ion conductors, proton con- ductors,...
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The first modern ex- periment was performed by Martin Fleischmann and B.. Stanley Pons at the University of Utah in early 1985.. Fritz Paneth and Kurt Peters of the University of Berlin preceded Fleischmann and Pons with a similar experiment in 1926.. Fleischmann and Pons used an electrochemical method of generating nuclear energy, in the form of heat, in a...
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It may seem something of a truism to describe an element as unique, but hydrogen is certainly one of the more unusual elements in the periodic table. It is the lightest element and consists of only a proton and an electron and is thus the only element not to contain a neutron in its main isotope ( 1 H). it...