Electrolysis

under electrolysis (griech. “by means of electricity”) understands one separates the fragmentation of a chemical compound by the effect of the electric current. One calls the tension, which must be applied thereby at least, separation potential. This sits down from thatRedox potential off, which would become free with the galvanic element, as well as one manufactured, the latter is needed again for production by titanium. The alkali metals and most alkaline earth metals are won by electrolysis, furthermore the halogens Fluor, Brom and Chlor,approximately for further syntheses in large yardstick one uses. Also the galvanic shop is based on electrolyses.

Metal separations belong to most important applications, either - as the examples specified above point - for the production of elementary metals as such or toProduction of metallic coats with the galvanic shop or for the production of conductive strips in processor production, in addition for the cleaning and separation from metals with the electrical refining. As the above examples show, in addition, nonmetals are electrolytically won like the halogens.Particularly to mention are hydrogen and oxygen, which are very in principle easily accessible by water electrolysis. So far it was however mostly cheaper to win hydrogen from oil or natural gas and oxygen from air while the electrolysis only in areas, in those cheap river was profitable, z. B. from water power, was available. If natural gas and oil and from it won fuels continue to increase in price, then it is to expect that in the future water electrolysis by means of electricity z. B. from solar electricity andin particular comes to the nuclear fusion for the production of hydrogen as source of energy a special meaning.

With the electrolysis electrical is converted into chemical energy. Particularly in case of of hydrogen and oxygen also the reversal is used, the production by electricity inthe gas cell, which would be together with water electrolysis central component of a future hydrogen economy.

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to history

1800 Alessandro Volta invented the first useful battery, volt ash column. With this power source for the first time also purposeful applications of the electrolysis were possible, and soon thereafter them were used - particularly of Humphry Davy in the years 1807 and 1808, in order to manufacture the up to then unknown elements sodium, potassium, barium, strontium, calcium and magnesium. Michael Faraday examined the electrolysis more exactly and discovered their Basic Law, i.e. the dependence of the converted massesof charge and mol mass. In addition Faraday created also the terms electrolysis, electrode, electrolyte, anode, cathode, anion and cation, published in his work 1832/1834.

1886 developed Paul Louis Toussaint Héroult and Charles MartinResound an electrolysis method for the production of aluminum, which is called today after the discoverers resound Héroult Process and which is basis of today's procedures. Already two years later were created companies, which used these, and 1900 was electrolytically won already 80,000 tons aluminum.

principles

the electrolysis is a procedure, which is forced by the electrical tension applied from the outside: The voltage supply causes an electron deficiency (“electron suction”) in the electrode connected with the positive terminal and an electron excess (“electron pressure”) in the other one, alsothe negative pole connected electrode. The electro-chemical oxidation effected at the anode and exists in an electron withdrawal by the electrode: The anode is with the electrolysis the positively charged electrode (positive terminal), the cathode is the negative pole. Thus the tension during thatElectrolysis remains upright received, must be supplied from the outside energy, and electric currents flow: The voltage supply brings electrons of the anode, thus from the positive terminal, to the negative pole, which is only possible, by carrying an appropriate work out. It “pumps” electronsfrom the anode to the cathode. So that the electric circuit remains closed, the same amperage must prevail in electrolytes, whereby the charge transfer takes place here via the ions: the negatively charged anions move preferentially to the positively charged anode, the positively charged cations move tonegatively charged cathode. The transition between electron conduction and ionic conduction takes place via the procedures at the electrodes.

experimental setup


Description:
  1. PDA for logging the produced quantities (not compellingly necessary)
  2. of switches for the activation of the electrolysis
  3. ammeter
  4. voltmeter
  5. electrolysis piston
  6. power supply unit, stabilizes

applications

electrolysis of water

the electrolysis of water consist of 2 Teilreaktionen, which run off at the 2 electrodes. The electrodes dive into water, which is made better leading by the addition by something sulfuric acid.

Positively charged Oxonium ions (H 3 O +) move in the electrical field to the negatively charged electrode (cathode), where they take up an electron in each case. Develop hydrogen atoms, which unite with a further H-atom resulted from reduction to a hydrogen molecule. Remainingremain water molecules.

2 H 3 O + + 2 e - → H 2 + 2 H 2 O

the separated, gaseous hydrogen ascends at the cathode.

To the positively charged electrode (anode) the negatively charged hydroxyl ions move. Each hydroxyl iondelivers two electrons to the positive pole, so that oxygen atoms develop, which unite to Sauerstoff-Molekülen. The remaining remaining H + - ions are neutralized immediately from hydroxyl ions to water molecules.

4 OH - → O 2 + 2 H 2 O+ 4 e -


the separated oxygen ascends also here as colorless gas at the anode.

The total reaction equation of the electrolysis of water reads:

4 H 3 O + + 4 OH - → 2 H 2 + O 2+ 6 H 2 O

the Oxonium and hydroxyl ions standing on the left side come of the Autoprotolyse the water:

8 H 2 O → 4 H 3 O + + 4 OH -

one knows the electrolysis equation therefore also as followswrite:

8 H 2 O → 2 H 2 + O 2 + 6 H 2 O

and/or. after shortening the water:

2 H 2 O → 2 H 2 + O 2

this is then the well-known equation, howit in many school books to find is.

The efficiency of the electrolysis of water is with approx. 70 %. With the alkaline electrolysis with approximately 90%. When using iridium dioxide catalysts as anode, platinum as cathode and by-fluoridated sulfone-acid diaphragms (Nafion)as electrolyte recently efficiencies were reached of 93%. The energetic view is for example with the use of hydrogen as source of energy necessary.

Little documented the electro-dynamic electrolysis, in which the ions in a pulsating electrical and magnetic field are accelerated.For the optimization of the efficiency also rise in temperature and photon irradiation (solar hydrolysis) can find employment. Also vacuum can be used in the extraction by gas-like electrolysis products efficiency-increasing.

Special cases of the electrolysis are the Voltammetrie and the polarography. Here one uses thoseMeasurement of the electrolysis stream, as a function of the tension, in order to receive explanation about the chemical composition to electrolytes.

quantitative analysis

the decomposition of electrolytes by electric current is used in electrical gravimetry and in the Coulometrie, overTo attain information about the metal content of a sample.

manufacturers of electrolysis plants (A-Z)

  • AccaGen (Switzerland)
  • Ammonia Casale
  • Hidroenergia VCST
  • IHT (Switzerland)
  • proton Energy system Incorporated
  • Norsk hydraulic Electrolysers AS (Norway)
  • Stuart Energy Europe NV (Belgium)
  • Teledyne Energy of systemInc.
  • The Electrolyser corporation Ltd. (Canada)
  • Outokumpu Technology (Finland, Germany)

see also

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