How PEM electrolysis works
A proton exchange membrane (also called a solid polymer electrolyte) cell passes current through pure water held against a thin polymer membrane. Water splits at the anode; protons cross the membrane and recombine into hydrogen gas on the other side. Nothing is added to the water and no caustic liquid is required.
Because hydrogen is formed on its own side of the membrane, the two gas streams can be kept apart by design rather than by downstream filtering.
Contaminants
The realistic contaminants in a consumer cell are residual oxygen carried across from the anode side, water vapour, and trace material shed by low-quality electrodes or fittings. Tap-water minerals are the other common source, which is why distilled or purified feed water is specified for these machines.
Alkaline cells that use a liquid electrolyte typically deliver an undifferentiated mixed gas, so the same separation question does not have a clean answer.
Purity levels
Purity is expressed as a percentage of hydrogen in the delivered gas stream, measured at the outlet. A figure is only meaningful when it names the test method, the laboratory and the sample — otherwise it is marketing text.
Our reports are published so buyers can read the method rather than take the number on trust. These describe hardware and manufacturing quality, not medical or therapeutic status.
Consumer vs industrial PEM
The same electrolysis chemistry scales up to industrial duty, where hydrogen is fed to engines and burners rather than inhaled. Those systems optimise for throughput and cost per cubic metre; consumer wellness systems optimise for quiet operation, stable low flow and a clean measurable outlet stream.