Definition
In a PEM cell, water contacts a catalyst-coated membrane. Applying direct current drives protons across the membrane, producing hydrogen on the cathode side and oxygen on the anode side.
The contrast is with alkaline or mixed-gas cells, which use a liquid electrolyte and can deliver hydrogen and oxygen together as a combined stream.
Modality relevance
The same cell chemistry serves both consumer modalities — the hydrogen stream can be routed to a cannula for inhalation or to a diffuser for bathing.
Purity relevance
Membrane separation is the structural reason PEM output can be specified and independently measured. Purity claims here describe manufacturing quality of the stack and gas path.
Science relevance
Electrolysis is settled electrochemistry. The open questions in hydrogen research concern biology, not whether the cell produces hydrogen.