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Reversible Hydrogen Electrode
A reversible hydrogen electrode (RHE) is a reference electrode, more specifically a subtype of the standard hydrogen electrodes, for electrochemical processes. Unlike the standard hydrogen electrode, its measured potential does change with the pH, so it can be directly used in the electrolyte. The name refers to the fact that the electrode is directly immersed in the actual electrolyte solution and not separated by a salt bridge. The hydrogen ion concentration is therefore not 1 mol/L, or 1 mol/kg, but corresponds to that of the electrolyte solution. In this way, it is possible to achieve a stable potential with a changing pH value. The potential of the RHE correlates to the pH value: : E = 0.000 - 0.059\times\mathrm In general, for a hydrogen electrode in which the reduction of the hydronium ions () occurs: : + + or, more often commonly written simply with denoting : : + with, : K = \frac the equilibrium potential depends on the hydrogen pressure and the ac ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Reference Electrode
A reference electrode is an electrode which has a stable and well-known electrode potential. The high stability of the electrode potential is usually reached by employing a redox system with constant (buffered or saturated) concentrations of each participant of the redox reaction. There are many ways reference electrodes are used. The simplest is when the reference electrode is used as a half-cell to build an electrochemical cell. This allows the reduction potential, potential of the other half cell to be determined. An accurate and practical method to measure an electrode's potential in isolation (absolute electrode potential) has yet to be developed. Aqueous reference electrodes Common reference electrodes and potential with respect to the standard hydrogen electrode (SHE): * Standard hydrogen electrode (SHE) (E = 0.000 V) activity of H+ = 1 Molar * Normal hydrogen electrode (NHE) (E ≈ 0.000 V) concentration H+ = 1 Molar * Reversible hydrogen electrode (RHE) (E = 0.000 V ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electrolysis Of Water
Electrolysis of water, also known as electrochemical water splitting, is the process of using electricity to decompose water into oxygen and hydrogen gas by electrolysis. Hydrogen gas released in this way can be used as hydrogen fuel, or remixed with the oxygen to create oxyhydrogen gas, which is used in welding and other applications. Electrolysis of water requires a minimum potential difference of 1.23 volts, though at that voltage external heat is required. E lectrolysis is rarely used in industrial applications since hydrogen can be produced less expensively from fossil fuels. History In 1789, Jan Rudolph Deiman and Adriaan Paets van Troostwijk used an electrostatic machine to make electricity that was discharged on gold electrodes in a Leyden jar with water. In 1800 Alessandro Volta invented the voltaic pile, and a few weeks later English scientists William Nicholson and Anthony Carlisle used it to electrolyse water. In 1806 Humphry Davy reported the results of ext ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electrodes
An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte, a vacuum or air). Electrodes are essential parts of batteries that can consist of a variety of materials depending on the type of battery. The electrophore, invented by Johan Wilcke, was an early version of an electrode used to study static electricity. Anode and cathode in electrochemical cells Electrodes are an essential part of any battery. The first electrochemical battery made was devised by Alessandro Volta and was aptly named the Voltaic cell. This battery consisted of a stack of copper and zinc electrodes separated by brine-soaked paper disks. Due to fluctuation in the voltage provided by the voltaic cell it wasn't very practical. The first practical battery was invented in 1839 and named the Daniell cell after John Frederic Daniell. Still making use of the zinc–copper electrode combination. Since then many more batteries have be ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Palladium-hydrogen Electrode
The palladium-hydrogen electrode (abbreviation: Pd/H2) is one of the common reference electrodes used in electrochemical study. Most of its characteristics are similar to the standard hydrogen electrode (with platinum). But palladium has one significant feature—the capability to absorb (dissolve into itself) molecular hydrogen. Electrode operation Two phases can coexist in palladium when hydrogen is absorbed: *alpha-phase at hydrogen concentration less than 0.025 atoms per atom of palladium *beta-phase at hydrogen concentration corresponding to the non-stoichiometric formula PdH0.6 The electrochemical behaviour of a palladium electrode in equilibrium with H3O+ ions in solution parallels the behaviour of palladium with molecular hydrogen :\tfrac \mathrm_2 = \mathrm_ = \mathrm_ Thus the equilibrium is controlled in one case by the partial pressure or fugacity of molecular hydrogen and in other case—by activity of H+-ions in solution. :E=E^0 + \ln When palladium is electroc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dynamic Hydrogen Electrode
A dynamic hydrogen electrode (DHE) is a reference electrode, more specific a subtype of the standard hydrogen electrodes for electrochemical processes by simulating a reversible hydrogen electrode with an approximately 20 to 40 mV more negative potential. Principle A separator in a glass tube connects two electrolytes and a small current is enforced between the cathode and anode. Applications * In-situ reference electrode for direct methanol fuel cells * 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 ...s See also * Palladium-hydrogen electrode References Electrodes Hydrogen technologies {{Electrochem-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Liquid Junction Potential
Liquid junction potential (shortly LJP) occurs when two solutions of electrolytes of different concentrations are in contact with each other. The more concentrated solution will have a tendency to diffuse into the comparatively less concentrated one. The rate of diffusion of each ion will be roughly proportional to its speed in an electric field, or their ion mobility. If the anions diffuse more rapidly than the cations, they will diffuse ahead into the dilute solution, leaving the latter negatively charged and the concentrated solution positively charged. This will result in an electrical double layer of positive and negative charges at the junction of the two solutions. Thus at the point of junction, a potential difference will develop because of the ionic transfer. This potential is called liquid junction potential or diffusion potential which is non-equilibrium potential. The magnitude of the potential depends on the relative speeds of the 'ions' movement. Calculation The ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sulfate
The sulfate or sulphate ion is a polyatomic anion with the empirical formula . Salts, acid derivatives, and peroxides of sulfate are widely used in industry. Sulfates occur widely in everyday life. Sulfates are salts of sulfuric acid and many are prepared from that acid. Spelling "Sulfate" is the spelling recommended by IUPAC, but "sulphate" was traditionally used in British English. Structure The sulfate anion consists of a central sulfur atom surrounded by four equivalent oxygen atoms in a tetrahedral arrangement. The symmetry is the same as that of methane. The sulfur atom is in the +6 oxidation state while the four oxygen atoms are each in the −2 state. The sulfate ion carries an overall charge of −2 and it is the conjugate base of the bisulfate (or hydrogensulfate) ion, , which is in turn the conjugate base of , sulfuric acid. Organic sulfate esters, such as dimethyl sulfate, are covalent compounds and esters of sulfuric acid. The tetrahedral molecular geometry of th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chloride
The chloride ion is the anion (negatively charged ion) Cl−. It is formed when the element chlorine (a halogen) gains an electron or when a compound such as hydrogen chloride is dissolved in water or other polar solvents. Chloride salts such as sodium chloride are often very soluble in water.Green, John, and Sadru Damji. "Chapter 3." ''Chemistry''. Camberwell, Vic.: IBID, 2001. Print. It is an essential electrolyte located in all body fluids responsible for maintaining acid/base balance, transmitting nerve impulses and regulating liquid flow in and out of cells. Less frequently, the word ''chloride'' may also form part of the "common" name of chemical compounds in which one or more chlorine atoms are covalently bonded. For example, methyl chloride, with the standard name chloromethane (see IUPAC books) is an organic compound with a covalent C−Cl bond in which the chlorine is not an anion. Electronic properties A chloride ion (diameter 167 pm) is much larger tha ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Current Density
In electromagnetism, current density is the amount of charge per unit time that flows through a unit area of a chosen cross section. The current density vector is defined as a vector whose magnitude is the electric current per cross-sectional area at a given point in space, its direction being that of the motion of the positive charges at this point. In SI base units, the electric current density is measured in amperes per square metre. Definition Assume that ''A'' (SI unit: m2) is a small surface centred at a given point ''M'' and orthogonal to the motion of the charges at ''M''. If ''I'' (SI unit: A) is the electric current flowing through ''A'', then electric current density ''j'' at ''M'' is given by the limit: :j = \lim_ \frac = \left.\frac \_, with surface ''A'' remaining centered at ''M'' and orthogonal to the motion of the charges during the limit process. The current density vector j is the vector whose magnitude is the electric current density, and whose dire ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cell Voltage
The volt (symbol: V) is the unit of electric potential, electric potential difference (voltage), and electromotive force in the International System of Units (SI). It is named after the Italian physicist Alessandro Volta (1745–1827). Definition One volt is defined as the electric potential between two points of a conducting wire when an electric current of one ampere dissipates one watt of power between those points. Equivalently, it is the potential difference between two points that will impart one joule of energy per coulomb of charge that passes through it. It can be expressed in terms of SI base units ( m, kg, s, and A) as : \text = \frac = \frac = \frac. It can also be expressed as amperes times ohms (current times resistance, Ohm's law), webers per second (magnetic flux per time), watts per ampere (power per current), or joules per coulomb (energy per charge), which is also equivalent to electronvolts per elementary charge: : \text = \text\Omega = \frac = \f ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Faraday Constant
In physical chemistry, the Faraday constant, denoted by the symbol and sometimes stylized as ℱ, is the electric charge per mole of elementary charges. It is named after the English scientist Michael Faraday. Since the 2019 redefinition of SI base units, which took effect on 20 May 2019, the Faraday constant has the exactly defined value given by the product of the elementary charge ''e'' and Avogadro constant ''N''A: : : :. Derivation The Faraday constant can be thought of as the conversion factor between the mole (used in chemistry) and the coulomb (used in physics and in practical electrical measurements), and is therefore of particular use in electrochemistry. Because 1 mole contains exactly entities, and 1 coulomb contains exactly elementary charges, the Faraday constant is given by the quotient of these two quantities: :. One common use of the Faraday constant is in electrolysis calculations. One can divide the amount of charge (the current integrated over time) ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Standard Hydrogen Electrode
The standard hydrogen electrode (abbreviated SHE), is a redox electrode which forms the basis of the thermodynamic scale of oxidation-reduction potentials. Its absolute electrode potential is estimated to be at 25 °C, but to form a basis for comparison with all other electrochemical reactions, hydrogen's standard electrode potential (''E''°) is declared to be zero volts at any temperature. Potentials of all other electrodes are compared with that of the standard hydrogen electrode at the same temperature. Nernst equation for SHE The hydrogen electrode is based on the redox half cell corresponding to the reduction of two hydrated protons, 2 H+(aq), into one gaseous hydrogen molecule, H2(g). General equation for a reduction reaction: : \text + z~e^ \rightleftharpoons \text The reaction quotient (') of the half-reaction is the ratio between the chemical activities (''a'') of the reduced form (the reductant, ) and the oxidized form (the oxidant, ). : Q_r = \frac ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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