The bifluoride ion is an inorganicanion with the chemical formula[HF2]−. The anion is colorless. Salts of bifluoride are commonly encountered in the reactions of fluoride salts with hydrofluoric acid. The commercial production of fluorine involves electrolysis of bifluoride salts.
Potassium bifluoride binds a second equivalent of HF:[5]
K[HF2] + HF → K[H2F3]
Heating these salts releases anhydrous HF.
The bifluoride anion is present in solutions of HF and buffered oxide etch, used in microfabrication etching. In these processes, bifluoride breaks down silicon oxides, doing more effectively than HF (~4.5 times faster).[6]