[ oxygen ] oxygen gases is EudraLex – Volume 4 – Good Manufacturing Practice( GMP) guidelines. Specifically of relevance is Annex 6: Manufacture of Medicinal Gases.
Annex 6 covers a diverse range of aspects, such as: premises and equipment; prevention of cross-contamination; filling operations; cylinder handling and storage; testing and quality control; and batch release, whereby a system of traceability must be put in place.
Using an electrolyser primarily for oxygen generation would be more power intensive than cryogenic air separation. However, if the oxygen is recovered as a by-product of hydrogen generation, electrolysis can be a low-cost mode of oxygen generation. Nonetheless, whilst oxygen may be a by-product of hydrogen electrolysis, once it has been packaged and delivered under the strict protocols, it would not be free to the patients.
Breathing applications and medical applications differ
On the International Space Station, water is split by electrolysis to generate oxygen for astronauts to breathe. Water contains 89 % oxygen by mass and can be transported in lightweight packaging. Therefore, transporting water into outer space for electrolysis is more efficient than taking compressed oxygen or liquid oxygen in heavy pressurised tanks.
Submarines also use electrolysers to generate oxygen for the crew to breathe during extended dives. The development of the world’ s first PEM electrolyser by GE in the 1960s was stimulated by the need to replace alkaline electrolysis on US military submarines.
Electrolytic oxygen may be good enough for submariners and astronauts. However, its use in medical applications must be approached with caution. Submariners and astronauts are selected for their physical fitness, whereas hospital patients requiring oxygen therapy are likely to be unwell and may be more susceptible to harm from any impurities in the oxygen.
High-purity oxygen from hydrogen electrolysers
Electrolysers configured for hydrogen production typically produce oxygen at 98 % purity, with hydrogen being the main impurity in the oxygen. Purification of oxygen is technically possible, but if there is no economic incentive, oxygen is vented to atmosphere.
Some companies, such as Teledyne Energy Systems, offer an oxygen purification module that can be used downstream of their TITAN™ EL electrolyser to ensure that the oxygen can be produced at 99.998 % purity.
The nature of the impurities must also be considered in any purity specification. For medicinal oxygen produced using an air separation unit, argon is the main impurity, with some nitrogen also present. Argon and nitrogen are also the main impurities in medicinal oxygen generated using a Pressure Swing Adsorption( PSA) or Vacuum Swing Adsorption( VSA) unit.
For electrolytic oxygen produced at 99.998 % purity, hydrogen could be present at up to 20 parts per million. If this oxygen were to be used for medical applications, it would be prudent to conduct clinical trials to determine what amount of residual hydrogen in electrolytic oxygen is acceptable.
Electrolyser technologies
There are several different types of electrolyser that convert water into oxygen and hydrogen. PEM units from ITM Power or Plug Power, and pressurised alkaline systems from Sunfire or
Hydrogen Tech World | Issue 22 | June 2025 39