The Russian oxygen generator on the ISS that produces oxygen by electrolysis of water is Elektron.
Elektron splits reclaimed water into oxygen and hydrogen. The oxygen is released into the station’s cabin for the crew to breathe, while the hydrogen is normally vented into space. Its name comes from the Russian system used aboard the Mir space station before the ISS era.
Elektron is part of the ISS Environmental Control and Life Support System. It has not always operated reliably: failures have led crews to use stored oxygen, Progress spacecraft supplies, or the Vika solid-fuel oxygen generator as backups. NASA also operates a separate U.S. Oxygen Generation System, so Elektron is not the station’s only oxygen source.
A common mix-up is Sabatier, which is not an oxygen generator. The Sabatier reactor combines carbon dioxide with hydrogen to recover water; that water can then become feedstock for oxygen production. Vozdukh removes carbon dioxide from the cabin, while Vika generates oxygen chemically rather than by water electrolysis.