Tài liệu miễn phí Hoá dầu
Download Tài liệu học tập miễn phí Hoá dầu
Electrocrystalization
Introduction: Electrocrystallization refers to nucleation and crystal growth occurring on electrodes in electrochemical systems under the influence of an electric field. 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 lead–acid battery the electrochemical reactions involve formation of different electronically conducting and insulating crystal phases (e.g., lead, lead dioxide (PbO2), lead sulphate (PbSO4), which have a decisive influence on the characteristics and operational life of the battery. ...
8/29/2018 7:09:10 PM +00:00
Electrokinetics
Introduction: Chemical systems are governed by three experimental variables (temperature, pressure, and composition), whereas electrochemical systems by four variables (temperature, pressure, composition, and electrical state). Thus, electrochemical systems enjoy an additional degree of freedom that makes them more versatile and easier to control. Chemical systems at equilibrium are unable to do or to receive work.
8/29/2018 7:09:10 PM +00:00
ELECTRODES
Introduction: 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.
8/29/2018 7:09:10 PM +00:00
Electrochemical kinetics
Current Flow in an Electrochemical Cell: Thermodynamic arguments permit the feasibility of overall cell reactions to be predicted, but give no information on rates. 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 Eeq (V) or electromotive force (emf). In the example of Figure 1, the cell contains hydrochloric acid as aqueous electrolyte and it divides into two compartments by a semipermeable membrane. In one compartment, hydrogen is dissolved and in the other one chlorine gas...
8/29/2018 7:09:10 PM +00:00
Non Faraday Electrochemical Modification of Catalysts Activity
Introduction: The term NEMCA refers to nonfaradaic electrochemical modification of catalytic activity. The NEMCA effect is also known as electrochemical promotion or electrochemical promotion of catalysis (EPOC) or electropromotion. It is the effect observed on the rates and selectivities of catalytic reactions taking place on electronically conductive catalysts deposited on ionic (or mixed ionic–electronic) supports upon application of electric current or potential (typically 72 V) between the catalyst and a second (counter or auxiliary) electrode also deposited on the same support. ...
8/29/2018 7:09:10 PM +00:00
Oxygen Evolution
Generalities: The formation of gaseous O2 at the anode of an electrolytic cell containing an aqueous electrolyte solution is the most frequent electrode reaction. It has immense practical implication because it always accompanies the electrolytic production of H2 in water electrolyzers, the cathodic deposition of metals in metal electrowinning processes, and the application of a cathodic current in cathodic protection operations, and it takes place at the negative pole of metal–air power sources upon recharging. ...
8/29/2018 7:09:10 PM +00:00
ELECTROCHEMICAL THEORY
The electrochemical cells are of extreme importance in physical chemistry and in everyday life, and several examples of the two main types of electrochemical cells are in widespread use in all areas of manufacture and energy storage. The electrochemical cell, or galvanic cell, is a device that converts chemical energy into electrical energy or vice versa when a chemical reaction is occurring.
8/29/2018 7:09:10 PM +00:00
Gel
Introduction: The rapid growth of the miniature electronic and computer-related industries has led to great demand for smaller and lighter batteries with improved safety, energy, and power characteristics. Lithium polymer batteries are expected to meet the above requirements and are thus considered as next-generation rechargeable batteries. The conventional lithium-ion batteries, which contain a large amount of liquid electrolyte, emit an appreciable amount of gas and this is attributed to the decomposition of a protective layer at the carbon surface. ...
8/29/2018 7:09:10 PM +00:00
Ion-Selective Electrodes
Introduction: An ion-selective electrode (ISE) is an example of an electrochemical sensor utilizing the principle of potentiometry, 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. To ensure a compliance with the Nernst equation, the very best commercially available potentiometers utilize a high input impedance 1013 O, and an appropriate operational amplifier in the electrometer to handle the associated minute currents. ...
8/29/2018 7:09:10 PM +00:00
Nanoelectrodes
Introduction: Nanoelectrode ensembles (NEEs) are nanotech-based electroanalytical tools that find application in a variety of fields ranging from electroanalysis to sensors and electronics. 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. The preparation of nanoelectrode using microporous membranes as templates distinguishes itself for its simplicity and wide applicability. ...
8/29/2018 7:09:10 PM +00:00
Porous Electrodes
Introduction: Most electrochemical reactions take place at the interface of two or more phases. Hence the area of reaction plays a vital role in determining the efficiency of an electrochemical process, just like in any surface reaction. There are several ways to increase the available area for reaction in an electrochemical cell: multiple electrodes are stacked alternatively, bipolar electrodes are used, and, sometimes, the reaction surface is modified by etching or coating with large surface area particles. ...
8/29/2018 7:09:10 PM +00:00
Semiconductor Electrodes
Introduction: The modern interest for phenomena at the semiconductor–electrolyte interface dates back to experiments 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 heterogeneous photocatalysis to sensors. The subject is highly interdisciplinary and involves fields like electrochemistry, solid-state physics, and surface science.
8/29/2018 7:09:10 PM +00:00
Solid: Mixed Ionic-Electronic Conductors
Introduction: Mixed ionic–electronic conductors (MIECs) have been and continue to be of interest for strategic applications related to energy conversion and environmental monitoring including batteries, fuel cells, permeation membranes, and sensors. Within solid oxide fuel cells (SOFCs), for instance, nanostructured ionic and electronic conducting materials can increase the electrochemical performance of the cathode and thus could potentially facilitate lower-temperature operation and thereby provide faster start-up times, improved stability, and less complicated thermal management. ...
8/29/2018 7:09:10 PM +00:00
Non-Aqueous
Introduction: Modern research on nonaqueous batteries is focusing on lithium-based systems, which require electrolyte solutions stable in the presence of metallic lithium and other anodes such as LiC6, which have potentials very close to the Li/Liþ reversible potential. For this reason, this article reviews the state-of-the-art of aprotic solvents, and reviews on protic solvents such as alcohols can be found in Further Reading. The selection of the aprotic electrolyte solution for a given battery system will have a major influence on performance such as power capability, operational temperature range, and in some cases on the maximum specific energy and energy...
8/29/2018 7:09:10 PM +00:00
ELECTROLYTES
Introduction: The electrolyte solution is a major component of all battery systems and as such will greatly influence energy densities (thermodynamic properties such as Gibbs energy, enthalpy, and ionic activity) and power densities (nonthermodynamic properties such as viscosity, conductivity, and transference). The electrolyte solution consists of a liquid or solid phase containing at least one component, e.g., water, which is called the solvent, and an ionizable substance, e.g., a salt or an acid, which is called the electrolyte. ...
8/29/2018 7:09:10 PM +00:00
Polymer
Introduction: Other than in solutions or in ionic liquids, ionic conduction can take place in the solid state also. The solids that exhibit ionic conduction are called ‘solid-state ionic conductors’. Based on the charge of ionic species responsible for the conduction, they are divided into cationic and anionic conductors; then, based on specific species involved in the conduction, they are further subdivided into sodium ion conductors, proton conductors, fluorine ion conductors, and so on. Electrolytes in which the solid conductor is a polymer are more specifically referred to as polymer electrolytes (or ionomers). ...
8/29/2018 7:09:10 PM +00:00
Cold Fusion: History
Introduction: Research on low-energy nuclear reactions (LENRs) originated as the result of an electrolysis experiment that used the elements palladium (a heavy metal) and deuterium (an isotope of hydrogen). The first modern experiment 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 way previously unrecognized by nuclear physicists. The two electrochemists announced their work...
8/29/2018 7:09:10 PM +00:00
Solid: Protons
Introduction: 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 (1H). In its stable molecular form (H2), it is also the least dense and the most abundant in the universe. Perhaps surprisingly, given that its low density results in gaseous hydrogen being almost nonexistent in the Earth’s lower atmosphere, it is also the...
8/29/2018 7:09:10 PM +00:00
Solid: Sodium Ions
Introduction: The ceramic oxide known as ‘beta alumina’ exhibits remarkably high conductivity of sodium ions and, as a consequence, has been adopted as a key component in batteries that employ liquid sodium as the active material at the negative electrode. Most rechargeable (or ‘secondary’) batteries comprise solid electrodes and a liquid electrolyte. A separator is placed in the electrolyte between the plates to prevent a short circuit.
8/29/2018 7:09:10 PM +00:00
Cold Fusion – Precursor to Low-Energy Nuclear Reactions
Introduction: On 23 March 1989, electrochemists M. Fleischmann and S. Pons claimed in a press conference at the University of Utah that they had achieved nuclear fusion in a tabletop chemistry experiment. Since then, evidence of fusion in what is now called low-energy nuclear reaction (LENR) research has grown only slightly stronger. Their hypothesis that a novel form of thermonuclear fusion was responsible for their experimental results is still unproved. On the contrary, LENR experiments have continued to demonstrate increasingly convincing evidence for some sort of nuclear process or processes – though not necessarily fusion – year after year. ...
8/29/2018 7:09:10 PM +00:00
ENERGY
Introduction: Today, the energy supply is primarily based on the combustion of fossil fuels. Electricity generation is the main driver for carbon dioxide emissions in stationary applications, whereas vehicles powered by internal combustion engines are a major source of distributed carbon dioxide emissions. The generation of electricity from renewable energy sources such as solar power, wind power, tidal power, or the use of biomass is reducing the burden from carbon dioxide emissions. In addition, the advent of hybrid or pure electric vehicles can drastically reduce mobility-related carbon dioxide emissions. ...
8/29/2018 7:09:10 PM +00:00
Hydrogen Economy
Introduction: A sustainable energy future with a stable global climate is central to the present worldwide debate on climate change due to the emissions of carbon dioxide (CO2), which is the main greenhouse gas (GHG) from human activities. The grand challenges faced by mankind in the coming years are the creation of a sustainable energy system caused by the depletion of fossil fuel resources (or their availability at a reasonable cost) due to the rapid growth of the world population and the related strong increase in energy demand and the negative impacts on the global climate due to large uncontrolled...
8/29/2018 7:09:10 PM +00:00
Manganese
Introduction Manganese dioxide (MnO2) has been successfully used as inexpensive and abundant battery material since its introduction in zinc–carbon batteries (with ammonium ´ chloride electrolyte) by G. L. Leclanche, in 1866. Initially, naturally occurring MnO2 was used followed by chemically synthesized manganese dioxide substantially ´ improving the performance of Leclanche batteries. Later, the more efficient electrochemically prepared manganese dioxide (EMD) was applied enhancing cell capacity and rate capability. ...
8/29/2018 7:08:57 PM +00:00
Iron
Introduction Iron is the second most commonly used metal after aluminum despite its most abundant nature. On the surface of the earth, iron occurs both in native (uncombined) form in very limited quantities and with other elements aplenty as its ores. By contrast, owing to the poor solubility (2.3 Â 10À8 mol LÀ1 or 1.3 Â 10À3 mg LÀ1) of iron oxides in water, iron is found only in limited amounts in the oceans as its hydrates, namely, [Fe(OH)2] þ and [Fe(OH)4]À.
8/29/2018 7:08:57 PM +00:00
Lead
Introduction Lead is a rare element present in the earth’s crust in a 1.4 Â 10À3% (w/w). It is a toxic heavy metal that exists only in a cubic close-packed metallic form. It shows the preference for the divalent state with electronic configuration [Xe]4f145d106s2 and low stability of the Pb–Pb covalent bond. Lead(IV) in solution is unstable (electronic configuration: [Xe]4f145d10). The most important Pb ore is galena (PbS). Other lead ores are anglesite (PbSO4), cerussite (PbCO3), mimetesite (Pb5(AsO4)3Cl), and pyromorphite (Pb5(PO4)3Cl). ...
8/29/2018 7:08:57 PM +00:00
Lithium
Introduction Because of its high reactivity, lithium metal is not found in its native state. The main sources of lithium are brine wells when subjected to evaporation as well as igneous rocks such as spodumine, lepidolite, and petalite. The name lithium comes from the Greek word ‘lithos’ meaning stone. Its discovery is generally attributed to Johan A. Arfvedson, who first identified it in 1817. Lithium metal was isolated by Sir Humphrey Davy and William Thomas Brande, and R. W. E. Bunsen and A. Maththiessen, in 1855 by the electrolysis of lithium chloride. ...
8/29/2018 7:08:57 PM +00:00
Zinc
Introduction In 1791, the first combination of metals in Volta’s battery involved zinc as the negative electrode. A zinc electrode was also used in subsequent Daniell, Grove, and Bunsen cells developed in the early nineteenth century. Those cells were strictly powered by zinc dissolution and cathodic hydrogen evolution. Improvements in battery power and capacity were achieved by increasing the electrode area and the volume of electrolyte, but the ultimate improvement required a new cathodic reaction and new porous cathode materials, leading to increased cathodic voltage and reduced cathodic polarization. ...
8/29/2018 7:08:57 PM +00:00
Nickel
Introduction Nickel alloys have been used since centuries for making coins, jewelry, and household utensils due to their hardness and relatively high oxidation resistance. Despite the wide spread of nickel minerals, the silvery-white metal was first recognized as a new element in 1751, when the Swedish mineralogist Axel Frederik Cronstedt discovered in niccolite an impure form of nickel. The name nickel originates from kupfernickel, a German name for niccolite, a copper-red color mineral containing B44% nickel and 56% arsenic. ...
8/29/2018 7:08:57 PM +00:00
Platinum
Introduction Electronic Structure The platinum group metals occupy the second and third rows of periodic table Group VIII, the first row of which consists of iron (Fe), cobalt (Co), and nickel (Ni). The second-row elements ruthenium (Ru), rhodium (Rh), and palladium (Pd) all have the krypton (Kr, inert gas, atomic number 36) core of completed electron shells and subshells (see Chemistry, Electrochemistry, and Electrochemical Applications: Oxygen).
8/29/2018 7:08:57 PM +00:00
Silver
The Chemistry of Silver Copper, silver, and gold form group 1B of the periodic table, and together they are known as the ‘coinage metals’. Silver, like gold and the six platinum group metals (platinum, palladium, rhodium, ruthenium, iridium, and osmium), is a noble metal. Silver has the highest electrical conductivity and the highest thermal conductivity of any metal, as well as the lowest electrical contact resistance (Table 1).
8/29/2018 7:08:57 PM +00:00