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How is elemental fluorine produced by electrolysis?

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A labeled diagram of the periodic table entry for fluorine, showing its atomic number 9, symbol F, atomic weight 18.998, electron configuration, and indicating it is a halogen and a gas at room temperature. — fluorine Properties of fluorine.

Elemental fluorine is produced through electrolytic procedures conducted in the absence of water. The process generally involves the electrolysis of a melt consisting of potassium fluoride and hydrogen fluoride.1

The electrolyte typically maintains a potassium fluoride-to-hydrogen fluoride ratio between 1:2.5 and 1:5. The process is carried out at varying temperature ranges, such as 30–70 °C (90–160 °F), 80–120 °C (180–250 °F), or 250 °C (480 °F). Because the hydrogen fluoride content of the electrolyte decreases during the reaction, causing the melting point to rise, it is necessary to add hydrogen fluoride continuously to maintain the process. In high-temperature cells, the electrolyte is replaced if the melting point exceeds 300 °C (570 °F).1

This method of isolating the element was famously developed by the French chemist Henri Moissan, who successfully prepared the highly reactive gas in 1886 by electrolyzing a solution of potassium fluoride in hydrofluoric acid.2