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Faraday Efficiency
Faraday efficiency (also called ''faradaic efficiency'', ''faradaic yield'', ''coulombic efficiency'' or ''current efficiency'') describes the efficiency with which charge (electrons) is transferred in a system facilitating an electrochemical reaction. The word "Faraday" in this term has two interrelated aspects. First, the historic unit for charge is the faraday, but has since been replaced by the coulomb. Secondly, the related Faraday's constant correlates charge with moles of matter and electrons (amount of substance). This phenomenon was originally understood through Michael Faraday's work and expressed in his laws of electrolysis. Sources of faradaic loss Faradaic losses are experienced by both electrolytic and galvanic cells when electrons or ions participate in unwanted side reactions. These losses appear as heat and/or chemical byproducts. An example can be found in the oxidation of water to oxygen at the positive electrode in electrolysis. Some electrons are diver ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electric Charge
Electric charge is the physical property of matter that causes charged matter to experience a force when placed in an electromagnetic field. Electric charge can be ''positive'' or ''negative'' (commonly carried by protons and electrons respectively). Like charges repel each other and unlike charges attract each other. An object with an absence of net charge is referred to as neutral. Early knowledge of how charged substances interact is now called classical electrodynamics, and is still accurate for problems that do not require consideration of quantum effects. Electric charge is a conserved property; the net charge of an isolated system, the amount of positive charge minus the amount of negative charge, cannot change. Electric charge is carried by subatomic particles. In ordinary matter, negative charge is carried by electrons, and positive charge is carried by the protons in the nuclei of atoms. If there are more electrons than protons in a piece of matter, it will h ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hydrogen
Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic, and highly combustible. Hydrogen is the most abundant chemical substance in the universe, constituting roughly 75% of all normal matter.However, most of the universe's mass is not in the form of baryons or chemical elements. See dark matter and dark energy. Stars such as the Sun are mainly composed of hydrogen in the plasma state. Most of the hydrogen on Earth exists in molecular forms such as water and organic compounds. For the most common isotope of hydrogen (symbol 1H) each atom has one proton, one electron, and no neutrons. In the early universe, the formation of protons, the nuclei of hydrogen, occurred during the first second after the Big Bang. The emergence of neutral hydrogen atoms throughout the universe occur ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Overpotential
In electrochemistry, overpotential is the potential difference (voltage) between a half-reaction's thermodynamically determined reduction potential and the potential at which the redox event is experimentally observed. The term is directly related to a cell's ''voltage efficiency''. In an electrolytic cell the existence of overpotential implies that the cell requires more energy than thermodynamically expected to drive a reaction. In a galvanic cell the existence of overpotential means less energy is recovered than thermodynamics predicts. In each case the extra/missing energy is lost as heat. The quantity of overpotential is specific to each cell design and varies across cells and operational conditions, even for the same reaction. Overpotential is experimentally determined by measuring the potential at which a given current density (typically small) is achieved. Thermodynamics The four possible polarities of overpotentials are listed below. * An electrolytic cell's anode ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Stoichiometric
Stoichiometry refers to the relationship between the quantities of reactants and products before, during, and following chemical reactions. Stoichiometry is founded on the law of conservation of mass where the total mass of the reactants equals the total mass of the products, leading to the insight that the relations among quantities of reactants and products typically form a ratio of positive integers. This means that if the amounts of the separate reactants are known, then the amount of the product can be calculated. Conversely, if one reactant has a known quantity and the quantity of the products can be empirically determined, then the amount of the other reactants can also be calculated. This is illustrated in the image here, where the balanced equation is: : Here, one molecule of methane reacts with two molecules of oxygen gas to yield one molecule of carbon dioxide and two molecules of water. This particular chemical equation is an example of complete combustion. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Self-discharge
Self-discharge is a phenomenon in batteries in which internal chemical reactions reduce the stored charge of the battery without any connection between the electrodes or any external circuit. Self-discharge decreases the shelf life Shelf life is the length of time that a commodity may be stored without becoming unfit for use, consumption, or sale. In other words, it might refer to whether a commodity should no longer be on a pantry shelf (unfit for use), or no longer on a ... of batteries and causes them to have less than a full charge when actually put to use. How fast self-discharge in a battery occurs is dependent on the type of battery, state of charge, charging current, ambient temperature and other factors. Primary batteries are not designed for recharging between manufacturing and use, thus have battery chemistry that has to have a much lower self-discharge rate than older types of secondary cells, but have lost that advantage with the development of rechargeable secon ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Work (thermodynamics)
In thermodynamics, work is one of the principal processes by which a thermodynamic system can interact with its surroundings and exchange energy. An exchange of energy is facilitated by a mechanism through which the system can spontaneously exert macroscopic forces on its surroundings, or vice versa. In the surroundings, this mechanical work can lift a weight, for example. The externally measured forces and external effects may be electromagnetic,Guggenheim, E.A. (1985). ''Thermodynamics. An Advanced Treatment for Chemists and Physicists'', seventh edition, North Holland, Amsterdam, .Jackson, J.D. (1975). ''Classical Electrodynamics'', second edition, John Wiley and Sons, New York, .Konopinski, E.J. (1981). ''Electromagnetic Fields and Relativistic Particles'', McGraw-Hill, New York, . gravitational,North, G.R., Erukhimova, T.L. (2009). ''Atmospheric Thermodynamics. Elementary Physics and Chemistry'', Cambridge University Press, Cambridge (UK), . or mechanical (such as pressur ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cathode
A cathode is the electrode from which a conventional current leaves a polarized electrical device. This definition can be recalled by using the mnemonic ''CCD'' for ''Cathode Current Departs''. A conventional current describes the direction in which positive charges move. Electrons have a negative electrical charge, so the movement of electrons is opposite to that of the conventional current flow. Consequently, the mnemonic ''cathode current departs'' also means that electrons flow ''into'' the device's cathode from the external circuit. For example, the end of a household battery marked with a + (plus) is the cathode. The electrode through which conventional current flows the other way, into the device, is termed an anode. Charge flow Conventional current flows from cathode to anode outside of the cell or device (with electrons moving in the opposite direction), regardless of the cell or device type and operating mode. Cathode polarity with respect to the anode can be positi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Anode
An anode is an electrode of a polarized electrical device through which conventional current enters the device. This contrasts with a cathode, an electrode of the device through which conventional current leaves the device. A common mnemonic is ACID, for "anode current into device". The direction of conventional current (the flow of positive charges) in a circuit is opposite to the direction of electron flow, so (negatively charged) electrons flow out the anode of a galvanic cell, into an outside or external circuit connected to the cell. For example, the end of a household battery marked with a "-" (minus) is the anode. In both a galvanic cell and an electrolytic cell, the anode is the electrode at which the oxidation reaction occurs. In a galvanic cell the anode is the wire or plate having excess negative charge as a result of the oxidation reaction. In an electrolytic cell, the anode is the wire or plate upon which excess positive charge is imposed. As a result of this, an ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Proton Exchange Membrane Fuel Cell
A proton is a stable subatomic particle, symbol , H+, or 1H+ with a positive electric charge of +1 ''e'' elementary charge. Its mass is slightly less than that of a neutron and 1,836 times the mass of an electron (the proton–electron mass ratio). Protons and neutrons, each with masses of approximately one atomic mass unit, are jointly referred to as "nucleons" (particles present in atomic nuclei). One or more protons are present in the nucleus of every atom. They provide the attractive electrostatic central force which binds the atomic electrons. The number of protons in the nucleus is the defining property of an element, and is referred to as the atomic number (represented by the symbol ''Z''). Since each element has a unique number of protons, each element has its own unique atomic number, which determines the number of atomic electrons and consequently the chemical characteristics of the element. The word ''proton'' is Greek for "first", and this name was given to the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Journal Of Physical Chemistry
''The Journal of Physical Chemistry A'' is a scientific journal which reports research on the chemistry of molecules - including their dynamics, spectroscopy, kinetics, structure, bonding, and quantum chemistry. It is published weekly by the American Chemical Society. Before 1997 the title was simply ''Journal of Physical Chemistry''. Owing to the ever-growing amount of research in the area, in 1997 the journal was split into ''Journal of Physical Chemistry A'' (molecular theoretical and experimental physical chemistry) and ''The Journal of Physical Chemistry B'' (solid state, soft matter, liquids, etc.). Beginning in 2007, the latter underwent a further split, with ''The Journal of Physical Chemistry C'' now being dedicated to nanotechnology, molecular electronics, and related subjects. Editors-in-chief *1896–1932 Wilder Dwight Bancroft, Joseph E. Trevor *1933–1951 S. C. Lind *1952–1964 William A. Noyes *1965–1969 F. T. Wall *1970–1980 Bryce Crawford *1980–2004 Mos ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cold Fusion
Cold fusion is a hypothesized type of nuclear reaction that would occur at, or near, room temperature. It would contrast starkly with the "hot" fusion that is known to take place naturally within stars and artificially in hydrogen bombs and prototype fusion reactors under immense pressure and at temperatures of millions of degrees, and be distinguished from muon-catalyzed fusion. There is currently no accepted theoretical model that would allow cold fusion to occur. In 1989, two electrochemists, Martin Fleischmann and Stanley Pons, reported that their apparatus had produced anomalous heat ("excess heat") of a magnitude they asserted would defy explanation except in terms of nuclear processes. They further reported measuring small amounts of nuclear reaction byproducts, including neutrons and tritium. ("It is inconceivable that this mount of heatcould be due to anything but nuclear processes... We realise that the results reported here raise more questions than they provide a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Faraday-efficiency Effect
The Faraday-efficiency effect refers to the potential for misinterpretation of data from experiments in electrochemistry through failure to take into account a Faraday efficiency of less than 100 percent. Assumption about efficiency Until recent decades it was common to assume that the release of hydrogen and oxygen gas during electrolysis of water always has a Faraday efficiency of 100%. Pons and Fleischmann, and other investigators who reported the finding of anomalous excess heat in electrolytic cells, all relied on this popular assumption. No one bothered to measure the Faraday efficiency in their cells during the experiments. Many publications reporting the finding of excess heat included an explicit statement like: "The Faraday efficiency is assumed to be unity." Even if not explicitly stated so, these publications included this implicit assumption in the formulas used to calculate the cells' energy balance. Relevance to cold fusion Lacking any other plausible explanation, t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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