History of electrochemistry

The history of electrolysis describes the main steps that led to the discovery of electrolysis and the subsequent progress in their technical application.

Discovery of electrolysis, new syntheses, compounds and elements, first theories

The first useful and powerful battery, the voltaic pile, was completed by the Italian physicist Alessandro Volta in 1799. She was the first voltage source at all, which could cause a prolonged current flow. 1800 Volta reported his discovery to the President of the Royal Society, Joseph Banks. That same year, the first electrolyses were carried out: William Cruickshank decomposed salt water. William Nicholson and Anthony Carlisle showed that from water using electricity from the voltaic pile two gases in a 2:1 ratio arise. Johann Wilhelm Ritter was able to prove by the oxyhydrogen sample and using white phosphorus, the two gases were hydrogen and oxygen.

Knight sat already in 1799 with two metal sheets different voltage chains together so that he could receive a first voltage range of base up to the noble metals. Knight also realized that in the galvanic electricity chemical reactions. Humphry Davy examined the acid and base formation by litmus paper and so could already study the migration of ions in the course of electrolysis.

Theodor Grotthuss (1785-1822) gave in 1805 to a first theory of the decomposition of water. He assumed that by the voltage incur positive and negative hydrogen particles oxygen particles. However, according to this theory remained obscure the effect of salts, acids, bases in the electrolytic deposition. 1802 received Hisinger and Jöns Jakob Berzelius chlorate electrochemically from table salt, which they could not prove conclusively the result. But Kolbe confirmed in 1847 chlorate and from hypochlorous acid. Hisinger and Berzelius suggested that molecules (atoms ) has a positive and a negative pole would ( electropositive, electronegative ) - similar to a magnet.

Humphry Davy developed an experimental arrangement in which the positive and negative poles were in two separate vessels. He was able to show that the negative pole forms a weak caustic soda solution from a sodium sulfate solution and the positive pole of weak sulfuric acid. He then examined also the electrolysis of molten salts 1805-1807, which he used as a cathode, a platinum spoon, as the positive electrode a platinum wire. So he discovered the potassium in the electrolysis of molten caustic potash, ie potassium hydroxide, in 1807. A little later he received metallic sodium from caustic soda. These metals easily catch fire or run by the reaction with atmospheric oxygen, and accordingly called this discovery considerable excitement and interest shown. 1808 turned Davy metallic magnesium, calcium, strontium and barium forth.

In the novel metal by Karl Aloys Schenzinger the historical figures of electrochemistry were presented in an interesting form.

Understanding of the basic laws

Michael Faraday investigated from 1832, the electrolysis detail. By weighing the amount of substance deposited ( coulometric ), after a certain unit of time he could the quantity of electricity ( charging amount Coulomb A * S ) determined at a constant voltage. According to him, the Faraday constant is later called, which is the amount of charge and the amount of substance deposited into perspective for the deposition of 1 mole of compound (eg silver ) is a charge quantity of approximately 96,485 coulombs necessary. Is deposited multiply charged ion, the multiple charge of the ion at an integer multiple of the corresponding charge to be considered. These dependencies of the converted masses from the amount of charge and the molar mass called Faraday's laws today. Faraday also provided a table of cations and anions together. In addition, Faraday also created a number of concepts that were needed to describe the results, where he was a philosopher and mathematician from Cambridge, William Whewell, advise. So they coined the new terms electrolysis, electrode, electrolyte, anode, cathode, anion and cation, published in Faraday's work 1832/1834.

John Frederic Daniell appeared in 1835 a copper plate into a solution of copper sulfate and a zinc plate in a zinc sulfate solution. Both half-cells he separated by a diaphragm ( Tondiaphragma ). The Daniell cell has now been for some years the most important source of electrical energy. 1843, Robert Bunsen a very cheap battery with a zinc plate and a special coal in dilute sulfuric ago. She was until the invention of the dynamo by Werner von Siemens, the best source for electricity.

Charles Wheatstone developed the bridge circuit for the determination of resistors, Johann Christian Poggendorff invented the Poggendorffsche compensation circuit for determining the stresses, Friedrich Kohlrausch developed a method to measure the resistance of an electrolyte solution without polarization of the electrodes by means of alternating current, the carbon rush square-root law, so now conductivities are investigated by electrolyte solutions could.

Johann Wilhelm Hittorf recognized the different migration velocities of the ions in electrolysis, he introduced the transference number. Friedrich Kohlrausch studied the conductivities of concentrated to very dilute salt solutions and was able to find a linear relationship by graphically plotting the conductance and the square root of the salt concentration. In high dilution each ion has a very characteristic conductance. Kohlrausch introduced the Molar conductivity.

Svante Arrhenius and Wilhelm Ostwald studied the conductivities of weak acids, bases and salts in aqueous solutions. Based on the knowledge of Jacobus Henricus van ' t Hoff that the osmotic pressure and freezing point of a liquid is proportional to the number of individual particles are ionic solution, Arrhenius and Ostwald discovered the principle of dissociation of weak acids by conductivity measurements. Depending on the acid strength only part of the acid is present in ionic form. Ostwald ( 1881) deduced a law ( Ostwald dilution law cal ) for the calculation of conductivity as a function of concentration and acid strength.

In 1923, Peter Debye calculated, Erich Hückel and Lars Onsager, the interaction of ions with the dielectric constant of the solution and were able to make a more precise mathematical theory of conductivity determination. Knowing the dissociation of the ionic conductivity in aqueous solutions, was for the pH determination, monitoring of the conversion of electrolysis, the determination of salinity of solutions of unknown concentration is of great importance.

Max Julius Le Blanc determined the voltage values ​​(decomposition voltage) for material deposition from normal solutions, found a method to determine the individual electrode potentials and also introduced a oscilloscopic current-time measurement during electrolysis.

Hermann von Helmholtz coined on the basis of electrochemical work, the concepts of energy, free enthalpy ( reaction driving force, heat and state of order after a chemical reaction), and the dependence of an equilibrium of temperature.

Walther Nernst investigated the electrolyte concentrations in oxidation and reduction processes, and found a clear explanation for metallic deposits on the cathode and the anode releases of metals. Based on the electrolyte concentration using the Nernst equation thus deposition voltages and electrochemical redox equilibria were determined.

Nernst was the half- cell of a lapped with hydrogen platinum electrode in 1 M hydrochloric acid, which is in equilibrium with the hydrogen formation, the arbitrary standard normal potential 0 V. At this reference point were now all voltage values ​​of other redox equilibria are determined and a uniform electrochemical series are set up. Even with the Declaration of diffusion processes, Nernst was a pioneer next Cottrell.

Julius panel dealt with the surge ( electrochemistry ) of electrodes and developed for this mathematical formulation.

Oliver Wolcott Gibbs and Alexander Classen develop the basis for the qualitative and quantitative material separation of metal ions in aqueous solutions by the Electrogravimetry.

Technical Terms and progress of the theory in the second half of the 19th century

1851 C. Watts received an English patent on a cell for the electrolytic production of chlorate from salt solution, which already had some features of modern cells. Since, however, he still had no dynamo available, it has not been used; only after 1886 chlorate was prepared electro- synthetic. After the invention of powerful electrical generators - which were based on the work of Michael Faraday's way also - among other also in 1866 by Werner von Siemens, who took advantage of the dynamo-electric principle, meant that electric currents were cheaper. In the years before the turn of the century It conducted a stormy development of technical electrolysis: From 1870 onwards, copper was recovered electrolytically in Germany, France, England. Emil Wohlwill in 1875 made ​​improvements in copper, silver and gold refining in Norddeutsche Affinerie. Major locations of copper production in Germany were Mansfeld, Oker and the North German Affinerie (now Aurubis AG) in Hamburg. The copper refining began in the United States since 1892. In 1910, the electrolytic copper production in the U.S. was already over 400,000 tons.

1890 led Hamilton Castner an eponymous cell for the electrolysis of molten sodium hydroxide. Here, the cylindrical cathode, which is located in the center of an anode tube of nickel separated by a iron wire net cylinder of the anode. A bus picks up the bell resulting sodium. 1892 invented Hamilton Castner in the U.S. and Karl Kellner in Austria mercury process for chlor-alkali electrolysis. This makes use of that sodium dissolves as amalgam in a mercury cathode, while the formation of hydrogen at the cathode is prevented by the high overvoltage. In 1890, the first plant for the production of chlorine and alkali on the diaphragm cell (see chlor-alkali electrolysis) was built in Griesheim, headed by Ignaz Stroof. Already in 1908 50.000 tons of sodium hydroxide could already be produced by this method.

The first works for the electrowinning of aluminum were made by Robert Bunsen and St. Claire- Deville. 1886 Ohio developed Paul Louis Toussaint Heroult and Charles Martin Hall, an electrolysis method for the extraction of aluminum, which is now named after the discoverers Hall - Heroult process and is the basis of today's proceedings. Two years later the company was founded, who used these, and 1900 80.000 tons of aluminum were already electrowinning. The method uses molten cryolite, Nariumhexafluoroaluminat, is dissolved in the alumina as electrolyte. The electrolysis is carried out at about 950 ° C, wherein the aluminum collected at the bottom of the electrolytic cell.

Upturn in the first half of the 20th century

The production using electrolysis method showed up to the downturn during the Second World War, in many cases, a strong growth. For example, over 600,000 tons of chlorine in 1940, made ​​in the USA. Hydrogen peroxide was then made ​​electro- synthesis, where sulfuric acid was electrolyzed. There arise peroxosulfuric and peroxodisulfuric or their salts, which can be hydrolyzed with water to form hydrogen peroxide. This procedure but was replaced in 1945 by chemical production methods.

The onset in the forties development of potentiostat, which make it possible to investigate electrochemical studies including electrolysis under more controlled conditions, since the processes at the counter electrode does not affect the potential measurement, fertilized the following exploration of the electrode processes.

Improvements and new syntheses in the second half of the 20th century

In 1968, patented by Beer electrodes made of titanium coated, for example with ruthenium dioxide. These so-called " dimensionally stable anodes " quickly became the material of choice for the electrolytic production of chlorine, as it is, in contrast to graphite, gradually oxidized and removed so that the surface, exhibit less wear and tear. In the late 1960s brought DuPont under the trade name " Nafion " ion exchange membranes from fully fluorinated polymer on the market, which combined a pronounced chemical stability with useful conductivity. This allowed the development of membrane processes for electrolysis. The electrolysis with the aim of chlorate production increased in the last decades of the 20th century a considerable upswing, which was based on the increasing demand for chlorine dioxide as a fiber- sparing and effective bleaching agent in the paper industry. Since chlorine dioxide does not feed, the production of chlorate and chlorine dioxide is usually done on site.

The strong demand for nylon made ​​in the mid-sixties, the company Monsanto to develop an electrolytic process for the production of a precursor of the need for nylon production Hexandiamins: The electrolytic synthesis of adiponitrile ( Hexandinitril ) of acrylonitrile ( propenenitrile ). In this case, the acrylonitrile is cathodically reduced, and dimerizes with protonation. By catalytic hydrogenation, then the desired hexanediamine.

Latest developments

Electrolysis of aqueous solutions, in which there is no hydrogen on the cathode instead of oxygen is reacted, require much lower voltages and therefore can save energy. Since the oxygen has to be brought in sufficient quantity to the cathode, special electrodes are necessary, so-called gas diffusion electrodes. The end of 2003, Bayer AG took in a hydrochloric acid electrolysis plant Brunsbuttel with oxygen depolarized cathodes in operation that can produce 20,000 tons of chlorine per year.

Date list

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