PEM (proton exchange membrane) electrolysis is the technology behind most modern high-purity hydrogen generation — from industrial green hydrogen production down to the wellness devices used for hydrogen water and hydrogen inhalation. Here's how it actually works, and how it compares to the older alkaline electrolysis approach it's increasingly replacing.
What is PEM electrolysis?
PEM electrolysis (sometimes called SPE, for solid polymer electrolyte) is a method of splitting water into hydrogen and oxygen gas using a solid polymer membrane rather than a liquid chemical electrolyte. The membrane sits between two electrodes and does two jobs at once: it conducts the ions needed for the electrolysis reaction to proceed, and it physically keeps the hydrogen and oxygen gas streams separated as they're produced.
How does PEM electrolysis work?
The process starts with water — typically purified or distilled water, fed to the anode side of the cell.
At the anode (oxygen side):
Water molecules are oxidised, releasing oxygen gas, positively charged hydrogen ions (protons), and electrons.
2H₂O → O₂ + 4H⁺ + 4e⁻
Through the membrane:
The protons (H⁺) pass through the solid polymer membrane to the cathode side. This is the defining feature of PEM technology — the membrane is proton-conductive, so only these positively charged ions cross through, while the gases stay separated on their respective sides.
At the cathode (hydrogen side):
The protons combine with electrons (delivered via the external circuit) to form hydrogen gas.
4H⁺ + 4e⁻ → 2H₂
The result: hydrogen gas collects on one side of the membrane, oxygen gas collects on the other, and — because pure or distilled water was used rather than a liquid electrolyte solution — both gas streams emerge free of any dissolved chemical carryover.
PEM vs. alkaline electrolysis
| PEM electrolysis | Alkaline electrolysis | |
|---|---|---|
| Electrolyte | Solid polymer membrane | Liquid alkaline solution (typically KOH or NaOH) |
| Feed water | Pure / distilled water | Water pre-mixed with alkaline electrolyte |
| Gas separation | At the membrane, during generation | Requires additional separation steps, or gases may be intentionally kept mixed |
| Typical gas purity | Very high (>99.99% achievable) | Lower, and dependent on electrolyte carryover/filtration |
| Maintenance | Minimal — no electrolyte to replace | Electrolyte solution requires periodic changing |
Alkaline electrolysis is an older, well-established technology with genuine industrial applications, and it's typically less expensive to manufacture at scale. PEM technology's advantage is purity and simplicity of maintenance — which is why it has become the dominant approach for applications, including wellness devices, where knowing exactly what's in the gas stream matters.
Why PEM matters for hydrogen wellness devices specifically
The wellness interest in hydrogen is specifically about breathing or consuming defined, high-purity molecular hydrogen (H₂). Because PEM technology:
- uses pure water with no added chemicals, and
- physically separates hydrogen and oxygen at the point of generation,
it allows a device to deliver a known, consistent gas composition — rather than an undefined mixture that may include carryover from a liquid electrolyte. This is also why PEM devices can safely offer the choice between breathing pure hydrogen, a combined hydrogen-oxygen flow, or splitting output between two users — the membrane gives the system precise control over each gas stream independently, something a mixed-gas alkaline system can't replicate.
For more on how this compares to older-style oxyhydrogen generation, see our companion article on Brown's Gas and HHO technology.
Where PEM electrolysis is used
- Green hydrogen production — PEM electrolysers are a leading technology for producing hydrogen fuel from renewable electricity at industrial scale.
- Fuel cells — the same membrane technology (in reverse) underlies hydrogen fuel cells.
- Wellness and inhalation devices — as described above, for delivering high-purity hydrogen or hydrogen-oxygen gas.
- Hydrogen-rich water generation — PEM cells are also used to infuse hydrogen gas into drinking water without altering its mineral content or pH.
This article is for general educational purposes and reflects publicly available technical information on PEM electrolysis. It does not constitute medical advice, and no claims are made regarding the diagnosis, treatment, or cure of any medical condition.