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In chemistry and manufacturing, electrolysis is a method of using an electric current to drive an otherwise non-spontaneous chemical reaction. Electrolysis is commercially highly important as a stage in the separation of elements from naturally-occurring sources such as ores using an electrolytic cell.

Overview
Electrolysis is the passage of an electric current through an ionic substance that is either molten or dissolved in a suitable solvent, resulting in chemical reactions at the electrodes and separation of materials.

The main components required to achieve electrolysis are:

A liquid containing mobile ions - an electrolyte
An external source of direct electric current
Two solid rods or plates known as electrodes
The components perform the following roles in the electrolysis process:

The mobile ions are the carriers of electrical current in the liquid (electrolyte). If the ions are not mobile, as in a solid salt then electrolysis cannot occur.
The externally supplied direct electric current supplies the energy necessary to create or discharge the ions in the liquid or solution. Electric current is carried by electrons in the external circuit.
The electrodes provide the physical interface between
The electrical circuit providing the energy to achieve the electrolysis
The electrolyte containing the ionic materials that are to be separated.
The electrodes must be able to conduct electricity. Electrodes of metal, graphite and semiconductor material are widely used. Choice of suitable electrode depends on:

Chemical reactivity between the electrode and electrolyte
Cost of manufacture of the electrode
Ancillary practical components to achieve electrolysis include:

Vessels to supply, contain and remove the reactants and products
Electrical circuitry

Process of electrolysis
The key process of electrolysis is the interchange of atoms and ions by the removal or addition of electrons from the external circuit. The required products of electrolysis are in some different physical state from the electrolyte and can be removed by some physical process. For example, in the electrolysis of brine to produce hydrogen and chlorine, the products are gaseous. These gaseous products bubble from the electrolyte and are collected.

A liquid containing mobile ions (electrolyte) is produced by

Solvation or reaction of an ionic compound with a solvent (such as an acid) to produce mobile ions
An ionic compound is melted (fused) by heating
An electrical potential is applied across a pair of electrodes immersed in the electrolyte.

Each electrode attracts ions that are of the opposite charge. Positively-charged ions (cations) move towards the electron-providing (negative) cathode, whereas negatively-charged ions (anions) move towards the positive anode.

At the electrodes, electrons are absorbed or released by the atoms and ions. Those atoms that gain or lose electrons to become charged ions pass into the electrolyte. Those ions that gain or lose electrons to become uncharged atoms separate from the electrolyte. The formation of uncharged atoms from ions is called discharging.

The energy required to cause the ions to migrate to the electrodes, and the energy to cause the change in ionic state, is provided by the external source of electrical potential.

Oxidation and reduction at the electrodes
Oxidation of ions or neutral molecules occurs at the anode, and the reduction of ions or neutral molecules occurs at the cathode. For example, it is possible to oxidize ferrous ions to ferric ions at the anode:
It is also possible to reduce ferricyanide ions to ferrocyanide ions at the cathode:
Neutral molecules can also react at either electrode. For example: p-Benzoquinone can be reduced to hydroquinone at the cathode:

In the last example, H + ions (hydrogen ions) also take part in the reaction, and are provided by an acid in the solution, or the solvent itself (water, methanol etc). Electrolysis reactions involving H + ions are fairly common in acidic solutions. In alkaline solutions, reactions involving OH − (hydroxide ions) are common.

The substances oxidised or reduced can also be the solvent (usually water) or the electrodes. It is possible to have electrolysis involving gases.
Energy changes during electrolysis
The amount of electrical energy that must be added equals the change in Gibbs free energy of the reaction plus the losses in the system. The losses can (in theory) be arbitrarily close to zero, so the maximum thermodynamic efficiency equals the enthalpy change divided by the free energy change of the reaction. In most cases, the electric input is larger than the enthalpy change of the reaction, so some energy is released in the form of heat. In some cases, for instance, in the electrolysis of steam into hydrogen and oxygen at high temperature, the opposite is true. Heat is absorbed from the surroundings, and the heating value of the produced hydrogen is higher than the electric input.
Related techniques
The following techniques are related to electrolysis:

Gel electrophoresis is an electrolysis using a gel solvent. It is used to separate substances, such as DNA strands, based on their electrical charge.
Electrochemical cells, including the hydrogen fuel cell, utilise differences in Standard electrode potential in order to generate an electrical potential from which useful power can be extracted. Although related via the interaction of ions and electrodes, electrolysis and the operation of electrochemical cells are quite distinct. A chemical cell should not be thought of as performing "electrolysis in reverse".

Faraday's laws of electrolysis
Main article: Faraday's laws of electrolysis

First law of electrolysis
In 1832, Michael Faraday reported that the quantity of elements separated by passing an electrical current through a molten or dissolved salt is proportional to the quantity of electric charge passed through the circuit. This became the basis of the first law of electrolysis.
Second law of electrolysis
Faraday also discovered that the mass of the resulting separated elements is directly proportional to the atomic masses of the elements when an appropriate integral divisor is applied. This provided strong evidence that discrete particles of matter exist as parts of the atoms of elements.

Industrial uses
Hall-Heroult process for producing aluminiumProduction of aluminium, lithium, sodium, potassium, magnesium
Coulometric techniques can be used to determine the amount of matter transformed during electrolysis by measuring the amount of electricity required to perform the electrolysis
Production of chlorine and sodium hydroxide
Production of sodium chlorate and potassium chlorate
Production of perfluorinated organic compounds such as trifluoroacetic acid
Production of electrolytic copper as a cathode, from refined copper of lower purity as an anode.
Electrolysis has many other uses:

Electrometallurgy is the process of reduction of metals from metallic compounds to obtain the pure form of metal using electrolysis. For example, sodium hydroxide in its molten form is separated by electrolysis into sodium and oxygen, both of which have important chemical uses. (Water is produced at the same time.)
Anodization is an electrolytic process that makes the surface of metals resistant to corrosion. For example, ships are saved from being corroded by oxygen in the water by this process. The process is also used to decorate surfaces.
A battery works by the reverse process to electrolysis. Humphry Davy found that lithium acts as an electrolyte and provides electrical energy.

Production of oxygen for spacecraft and nuclear submarines.
Electroplating is used in layering metals to fortify them. Electroplating is used in many industries for functional or decorative purposes, as in vehicle bodies and nickel coins.
Production of hydrogen for fuel, using a cheap source of electrical energy.[2]
Electrolytic Etching of metal surfaces like tools or knives with a permanent mark or logo.
Electrolysis is also used in the cleaning and preservation of old artifacts. Because the process separates the non-metallic particles from the metallic ones, it is very useful for cleaning old coins and even larger objects.

电解

电解（Electrolysis）是将电流通过电解质溶液或熔融态物质,又称电解液，而在阴极和阳极上引起氧化还原反应的过程叫电解的一种方法，电化学电池在外加电压时可发生电解过程。
　　即电流通过物质而引起化学变化的过程。化学变化是物质失去或获得电子(氧化或还原)的过程。电解过程是在电解池中进行的。电解池是由分别浸没在含有正、负离子的溶液中的阴、阳两个电极构成。电流流进负电极(阴极)，溶液中带正电荷的正离子迁移到阴极，并与电子结合，变成中性的元素或分子；带负电荷的负离子迁移到另一电极(阳极)，给出电子，变成中性元素或分子。
电解原理分析
　　（以cucl2为例）
　　CuCl2是强电解质且易溶于水，在水溶液中电离生成Cu2＋和Cl－。
　　CuCl2＝Cu2＋＋2Cl－
　　通电前，Cu2＋和Cl－在水里自由地移动着；通电后，这些自由移动着的离子，在电场作用下，改作定向移动。溶液中带正电的Cu2＋向阴极移动，带负电的氯离子向阳极移动。在阴极，铜离子获得电子而还原成铜原子覆盖在阴极上；在阳极，氯离子失去电子而被氧化成氯原子，并两两结合成氯分子，从阳极放出。
　　阴极：Cu2＋＋2e－＝Cu
　　阳极：Cl－－2e－＝ Cl2↑
　　电解CuCl2溶液的化学反应方程式：CuCl2=Cu+Cl2↑(电解）（5）电解质水溶液电解反应的综合分析
　　在上面叙述氯化铜电解的过程中，没有提到溶液里的H＋和OH－，其实H＋和OH－虽少，但的确是存在的，只是他们没有参加电极反应。也就是说在氯化铜溶液中，除Cu2＋和Cl－外，还有H＋和OH－，电解时，移向阴极的离子有Cu2＋和H+，因为在这样的实验条件下Cu2＋比H+容易得到电子，所以Cu2＋在阴极上得到电子析出金属铜。移向阳极的离子有OH－和Cl－，因为在这样的实验条件下，Cl－比OH－更容易失去电子，所以Cl－在阳极上失去电子，生成氯气。
　　说明：
　　①阳离子得到电子或阴离子失去电子而使离子所带电荷数目降低的过程又叫做放电[1]。
　　②用石墨、金、铂等还原性很弱的材料制做的电极叫做惰性电极，理由是它们在一般的通电条件下不发生化学反应。用铁、锌、铜、银等还原性较强的材料制做的电极又叫做活性电极，它们做电解池的阳极时，先于其他物质发生氧化反应。
　　③在一般的电解条件下，水溶液中含有多种阳离子时，它们在阴极上放电的先后顺序是：Ag+＞Hg2+＞Fe3+＞Cu2+＞Pb2+>Sn2+>Fe2+＞Zn2+>H+>Al3+>Mg2+>Na+>Ca2+>K+；水溶液中含有多种阴离子时，它们的惰性阳极上放电的先后顺序是：S2->I->Br->Cl->OH->含氧酸根>F-。
　　（6）以惰性电极电解电解质水溶液，分析电解反应的一般方法步骤为：
　　①分析电解质水溶液的组成，找全离子并分为阴、阳两组；
　　②分别对阴、阳离子排出放电顺序，写出两极上的电极反应式；
　　③合并两个电极反应式得出电解反应的总化学方程式或离子方程式。
用途
　　电解广泛应用于冶金工业中，如从矿石或化合物提取金属(电解冶金)或提纯金属(电解提纯)，以及从溶液中沉积出金属(电镀)。金属钠和氯气是由电解溶融氯化钠生成的；电解氯化钠的水溶液则产生氢氧化钠和氯气。电解水产生氢气和氧气。水的电解就是在外电场作用下将水分解为H2（g）和O2（g）。电解是一种非常强有力的促进氧化还原反应的手段，许多很难进行的氧化还原反应，都可以通过电解来实现。例如：可将熔融的氟化物在阳极上氧化成单质氟，熔融的锂盐在阴极上还原成金属锂。电解工业在国民经济中具有重要作用，许多有色金属（如钠、钾、镁、铝等）和稀有金属（如锆、铪等）的冶炼及金属（如铜、锌、铅等）的精炼，基本化工产品(如氢、氧、烧碱、氯酸钾、过氧化氢、乙二腈等)的制备，还有电镀、电抛光、阳极氧化等，都是通过电解实现的。
电解质
　　在水溶液里或熔融状态下能导电的化合物叫电解质。化合物导电的前提：其内部存在着自由移动的阴阳离子。
　　离子化合物在水溶液中或熔化状态下能导电；共价化合物：某些也能在水溶液中导电（如HC，其它为非电解质）
　　强电解质一般有：强酸强碱，大多数盐，活泼金属的氧化物、氢化物；弱电解质一般有：（水中只能部分电离的化合物）弱酸（可逆电离，分步电离<多元弱酸>，弱碱（如NH3·H2O）。另外，水是极弱电解质。
　　导电的性质与溶解度无关
　　注：能导电的不一定是电解质判断某化合物是否是电解质，不能只凭它在水溶液中导电与否，还需要进一步考察其晶体结构和化学键的性质等因素。例如，判断硫酸钡、碳酸钙和氢氧化铁是否为电解质。硫酸钡难溶于水(20 ℃时在水中的溶解度为2.4×10-4 g)，溶液中离子浓度很小，其水溶液不导电，似乎为非电解质。但溶于水的那小部分硫酸钡却几乎完全电离(20 ℃时硫酸钡饱和溶液的电离度为97.5％)。因此，硫酸钡是电解质。碳酸钙和硫酸钡具有相类似的情况，也是电解质。从结构看，对其他难溶盐，只要是离子型化合物或强极性共价型化合物，尽管难溶，也是电解质。
　　氢氧化铁的情况则比较复杂，Fe3+与OH-之间的化学键带有共价性质，它的溶解度比硫酸钡还要小(20 ℃时在水中的溶解度为9.8×10-5 g)；而落于水的部分，其中少部分又有可能形成胶体，其余亦能电离成离子。但氢氧化铁也是电解质。
　　判断氧化物是否为电解质，也要作具体分析。非金属氧化物，如SO2、SO3、P2O5、CO2等，它们是共价型化合物，液态时不导电，所以不是电解质。有些氧化物在水溶液中即便能导电，但也不是电解质。因为这些氧化物与水反应生成了新的能导电的物质，溶液中导电的不是原氧化物，如SO2本身不能电离，而它和水反应，生成亚硫酸，亚硫酸为电解质。金属氧化物，如Na2O，MgO，CaO，Al2O3等是离子化合物，它们在熔化状态下能够导电，因此是电解质。 需要注意的是，氯化铝(AlCl3)是电解质，但是是共价化合物而不是离子化合物。
　　可见，电解质包括离子型或强极性共价型化合物；非电解质包括弱极性或非极性共价型化合物。电解质水溶液能够导电，是因电解质可以离解成离子。至于物质在水中能否电离，是由其结构决定的。因此，由物质结构识别电解质与非电解质是问题的本质。
　　另外，有些能导电的物质，如铜、铝等不是电解质。因它们并不是能导电的化合物，而是单质，不符合电解质的定义。
　　电解质是指在水溶液中或熔融状态下能够导电的化合物，例如酸、碱和盐等。凡在上述情况下不能导电的化合物叫非电解质，例如蔗糖、酒精等。
　　电解生成物规律
　　十六字要诀：
　　阴得阳失 ：电解时，阴极得电子， 发生还原反应，阳极失电子，发生氧化反应；
　　阴精阳粗 ：精炼铜过程中,阴极使用精铜，阳极使用粗铜，最后阳极逐渐溶解，且产生阳极泥；
　　阴碱阳酸 ：在电解反应之后，不活泼金属的含氧酸盐会在阳极处生成酸，而活泼金属的无氧酸盐会在阴极处生成碱；
　　阴固阳气 ：电解反应之后，阴极产生固体及还原性气体，而阳极则生成氧化性强的气体。