Electrolytic cell

Electrolysis is the process of passing an electric current through an ionic conductor such as an electrolyte solution or a molten electrolyte to cause a chemical change, and the device that performs electrolysis is called an electrolytic cell. By applying electrical energy, electrolytic reactions can cause reactions that increase free energy, which is not possible with normal chemical reactions. However, electrolytic reactions occur two-dimensionally near the interface between the electrode and the electrolyte, and the amount of electricity that is related to the reaction is determined by the amount of electricity passing through the interface between the electrode and the electrolyte according to Faraday's law, and the reaction rate can be adjusted by the current density. The electrode into which the current flows is called the anode, and the electrode into which the current flows is called the cathode. Oxidation reactions occur at the anode, and reduction reactions occur at the cathode. There are two types of electrodes: temporary ones that are replaced when dissolved or when a certain amount of deposit accumulates, such as in metal refining or plating, and permanent ones that are used in water electrolysis and alkaline electrolysis. The potential difference required to maintain electrolysis is called the decomposition voltage.

[Toyohiko Hayakawa]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

電解質溶液や融解電解質などのイオン伝導体に電流を通じて化学変化をおこさせることを電気分解といい、電気分解を行う装置を電解槽という。電解反応は、電気的エネルギーを加えることにより、普通の化学反応ではおこりえない自由エネルギーの増加する反応もおこさせうる。しかし電解反応は二次元的に電極と電解液の界面近傍でおこり、反応に関係する量は、ファラデーの法則により電極と電解液の界面を通る電気量によって定まり、反応速度は電流密度によって調節できる。電流の流入する側の電極を陽極、流出する側の電極を陰極といい、陽極では酸化反応、陰極では還元反応がおこっている。電極には金属の精製やめっきのように溶解しさったり、あるいは析出物がある程度たまると取り換える一時的のものと、水電解や電解アルカリのように永久的に使用されるものとがある。なお、電解を維持するのに必要な電位差を分解電圧という。

［早川豊彦］

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