Electrochemically activated alkaline catholyte with рН over 9.0; symbolic notation: К catholyte. It is produced in STEL- АК devices by cathodic treatment of initial sodium chloride solution of 0.1-0.5 g/l concentration, or common fresh water with no additives, via transporting the main current portion through the diaphragm by oncoming movement of sodium and chlorine ions. In the process of synthesis, differential pressure on the diaphragm may vary from 0 to 0.2 kgf/cm2. Асtive components of catholyte K are represented by sodium hydroxides as well as by metastable aquacomplexes of hydroxil anion (ОН–), peroxide anion (НО2–), hydroperoxide anion (НО2–), molecular oxygen ion-radical (О2–), oxygen anion (О2-), peroxide anion (О22-), and metastable aquacomplexes of hydrogen superoxide (НО2), free hydrogen radical (Н.) and free peroxide radical (НО2.).